Soil properties under different orchard floor management systems for organic apple production Roberto J. Zoppolo, Dario Stefanelli, George W. Bird & Ronald L. Perry
Organic Agriculture Official journal of The International Society of Organic Agriculture Research ISSN 1879-4238 Org. Agr. DOI 10.1007/s13165-011-0018-z
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Author's personal copy Org. Agr. DOI 10.1007/s13165-011-0018-z
Soil properties under different orchard floor management systems for organic apple production Roberto J. Zoppolo & Dario Stefanelli & George W. Bird & Ronald L. Perry
Received: 30 March 2010 / Accepted: 28 November 2011 # Springer Science & Business Media BV 2011
Abstract Orchard floor management impacts soil conditions and thus tree performance. This research was initiated to investigate the effects of alternative orchard floor management systems compatible with organic production on soil parameters using the “Pacific Gala” apple cultivar (Malus × domestica Borkh.) on three rootstocks of varying vigor. Alfalfa hay mulch, propane flame burner, and Swiss sandwich system (combination of resident vegetation and tilled strips) were compared from 2001 to 2005. These treatments were applied to tree rows which provided different vegetation-free areas. Contrasting additions of organic matter were evaluated for their effect on soil organic matter (SOM), C content, nitrate and ammonium R. J. Zoppolo (*) Instituto Nacional de Investigación Agropecuaria (INIA) Las Brujas, Ruta 48 km-10, Canelones 90200, Uruguay e-mail:
[email protected] R. J. Zoppolo : D. Stefanelli : G. W. Bird : R. L. Perry Department of Horticulture, Michigan State University, East Lansing, MI 48824, USA D. Stefanelli e-mail:
[email protected] Present Address: D. Stefanelli Department of Primary Industries, Knoxfield Centre, 621 Burwood Highway, Knoxfield, VIC 3180, Australia
availability, moisture, and soil food web through nematode populations. Laboratory incubations to determine C and N mineralization potentials were performed. During this time period, SOM increased under the mulched soil and slightly less under the Swiss sandwich system (SSS) but in this last case without external inputs. Carbon and N pools were not impacted by flame burning (FL) but were enhanced by alfalfa hay mulch (MU) and to a lesser extent by SSS. Nitrate-N content in soil under MU increased between five and ten times compared to SSS and FL. Total number of nematodes was higher for SSS and MU compared with FL treatment; however, SSS had the most structured soil food web, an important sustainability trait, while MU had the least. Keywords Soil organic matter . Swiss sandwich system . Hay mulch . Propane flaming . C mineralization . Soil food web
Introduction Worldwide efforts toward developing more sustainable agricultural systems and the importance of organic production of fruits and vegetables have increased steadily in the last few decades (Dimitri and Greene 2002; Yussefi 2004). In fruit production, orchard floor management is a key component of the system with an increased importance under organic production conditions (Bloksma 2000; Tinsley 2000). The main objectives
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of orchard floor management are to maintain and/or increase the soil fertility and physical and biological properties and to supply nutrients and water to trees on demand. In organic fruit production, there is the need for a more sustainable approach to weed management compatible with organic protocols that provides careful utilization instead of suppression (Sooby et al. 2007; Granatstein and Sánchez 2009). The beneficial effects of soil covers have been studied under various conditions. These effects, depending on the type of soil cover used, include improvement of soil organic matter content, erosion control, soil moisture retention, competition with weed species, soil fertility enhancement, increased numbers of beneficial insects, improved fruit quality, and ease of equipment movement (Childers 1972; Hipps and Samuelson 1991; Hogue and Neilsen 1987). We hypothesize that changing soil cover in our orchards will have an effect on soil organic matter and fertility, in addition to tree performance and productivity as reported by Stefanelli et al. (2009). Soil is an integral part of the farming system and is considered the main support for life. Understanding the processes that take place within it is the basis for its sustainable management. Soil organisms influence every aspect of decomposition and nutrient availability (Magdoff and van Es 2000). Organic matter plays a central role in the construction of a healthy and productive soil (Magdoff and van Es 2000) healthy defined here as a soil that within natural or managed ecosystem boundaries is capable of providing all services to sustain plant and animal productivity (Doran et al. 1996). In organic fruit production, in contrast to conventional production that relies on regular fertilization, one of the main goals is to build organic matter in the soil (Bloksma 2000), the major food source for soil microorganisms. Organic matter is also an indicator of carbon stored in the soil (Stevenson 1994). Organic apple production should be carried out following the definitions and guidelines of the International Federation of Organic Agriculture Movements relying on ecological processes, biodiversity, and cycles adapted to local conditions (IFOAM 2010). Organic growers will rely on the soil food web to enhance nutrient availability for the plants, taking into account that N release from different sources varies with the quantity and quality of the material used and the soil environment (Brady and Weil 2002; Magdoff and van Es 2000; Myers et al. 1997; Wardle and Lavelle 1997). Orchard floor management systems (OFMS) can
change the microbial composition of the soil (Yao et al. 2005). Soil microorganisms are of great importance in ecosystem processes such as soil particle aggregation, decomposition and mineralization of organic matter, nutrient cycling and availability, and interaction with plants. There have been several studies on the effects of soil management systems on soil microbes and the structure of the soil food web (Ferris et al. 2004; Mader et al. 2002; Yao et al. 2005). Most of these studies have found higher soil respiration rates and soil bacterial populations with higher number and diversity of bacteria under living covers or organic mulches than under herbicide treated surfaces which has been suggested is due to increased available resources for microorganisms (Yao et al. 2005). Hoagland et al. (2008) reported improved biological activity with greater nematode abundance in living mulch treatments. Rhizosphere microorganisms may affect the hormonal balance and competitive ability of the plant, which will modify the soil biological community and the soil ecosystem (El-Shatnawi and Makhadmeh 2001). Factors which stabilize the microbial biomass and reduce turnover are likely to have important consequences for soil nutrient dynamics and plant growth and ecosystem productivity (Wardle 1998). Microorganism activity in the organic system influences the release of available nitrogen to the trees in the soil (Forge et al. 2003). Orchard floor management systems can provide organic forms of C and N which are quickly metabolized to inorganic nitrogen and other nutrients, primarily by bacteria and fungi (Ferris et al. 1998). Nitrogen is also mineralized as predators of bacteria and fungi, such as protozoa and microbivorous nematodes that graze on prey which contains more N than required by the predators (Ferris et al. 1998). Microbivorous organisms make up a large portion of the nematode community. Excess N generated by microbivorous grazing is released to the soil and becomes available for plant uptake (Ferris et al. 1998). Nematode feeding types have an overall positive contribution to soil and thus ecosystem processes (Bongers and Ferris 1999; Yeates 1987). Nematodes can be used as indicators of soil functionality and biodiversity (Yeates 2003) since they reflect the soil and ecological processes (Yeates 1999). Higher population of bacterivores indicates higher number of bacteria in soils. The different soil conditions generated by OFMS can affect soil biological composition, and this will be reflected in
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the relative nematode populations’ composition. Most of the studies on the benefits of nematodes on nutrient release and availability in the soil have been done on the bacterial and fungal feeder nematodes. Bacterial feeders are responsible for a greater release of N when soil conditions are closer to optimal (Ferris et al. 1996, 1998; Forge et al. 2003; Laakso et al. 2000) while fungal feeders have a higher effect when soil conditions are not optimal (Ferris et al. 1998, 2004; Ferris and Chen 1999; Ingham et al. 1985). A food web becomes more beneficial with increased structure and diversification (Garlaschelli 2004; Paine 1996; Power 1992; Sugihara et al. 1997). The interaction between the OFMS and the soil food web has an impact on conditions for plant development and nutrient availability. The degree to which kinetics of nutrient uptake or other potential adjustments are expressed would ultimately depend on soil nutrient availability and soil factors that determine nutrient transport to the root surface (Bassirirad 2000). The retention of nutrients within an ecosystem depends on temporal and spatial synchrony between nutrient availability and nutrient uptake (Tierney et al. 2001). OFMS that support the most diversified food web will be able to reach a balance in time with an increased probability of a self-sustainable environment, thus increasing the long-term productivity of the plants. In this experiment, we evaluated three different OFMS for their effect on organic matter in soil. One has a constant addition of N containing organic material (alfalfa hay mulch added twice yearly), the second has the constant destruction of organic material on the soil surface (flame burning) so there is no addition, and the third is a combination of what can be considered a modified cover crop (natural vegetation never mowed) and tillage. The OFMS also have a difference in regard to hand labor and machinery requirements for their application and management. We hypothesize that these different soil managements will have an impact on the soil C and N pools and organic matter content and therefore will impact the soil food web structure and diversity. The main objective of this study reported here was to determine the impact of alternative OFMS, compatible with organic production, on soil properties, conditions, and food web, all of which determine tree performance (Stefanelli et al. 2009).
Materials and methods Site description, plant material, and OFMS The orchard is located at the Horticultural Experiment Station of Michigan State University (latitude of 42° 84′ N and longitude of 84°24′ W) in the vicinity of Clarksville, MI, USA. This orchard of 2.5 ha changed into organic management in 1999 following the Organic Crop Improvement Association guidelines (OCIA 1998). The experiment was conducted from 2001 to 2005 in an experimental field that covers an area of 0.38 ha of the orchard. The predominant soil type is a Kalamazoo sandy clay loam (Typic Hapludalfs with 53.1% sand, 23.1% silt, and 23.8% clay) with mild slopes of less than 3%. The soil organic matter content at the beginning of the experiment was on average 1.8% with no significant differences among plots which translates into 14 and 42 t/ha of stored soil C at 0–10 and at 0–30 cm deep, respectively. One-year-old “Pacific Gala” apple trees (Malus × domestica Borkh.) grafted on three different rootstocks (M.9 NAKB 337, M.9 RN29, and Supporter 4) were planted in April 2000. Planting distance was adjusted according to the vigor of each rootstock and the acquired knowledge of their performance under Michigan conditions (Perry 2002). Distance between rows was 4.6 m while the distance between trees in the row was 1.4 m for M.9 NAKB 337, 1.7 m for M.9 RN29, and 2.0 m for Supporter 4. Plants were trained to a vertical axe (Perry 2000). The three different OFMS applied to plots (each replicated six times), as the main factor of a split-plot design, were: 1. Alfalfa hay mulch (MU): A 1-m strip on each side of the tree row covered with alfalfa hay mulch maintained from March to October at least 15 cm thick. The alfalfa bales were locally produced at a neighbor field, and the hay was hand-applied in spring and autumn. This treatment required the highest amount of hand labor. 2. Flame burning (FL): A 1-m strip on each side of the tree row kept free of vegetation through the use of a propane flame burner. The equipment used was specific for burning off vegetation and implied an important investment. 3. Swiss sandwich system (SSS): A central strip that spread 30 cm to each side of the tree row in which
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vegetation was allowed to grow (sandwich vegetated area, SVA) and a 70-cm-wide strip tilled (5– 10 cm deep) on each side of that vegetated central strip until 2003 and expanded to 90 cm wide from 2004 (sandwich tilled strip, STS) following the Swiss sandwich (Weibel 2002). A very simple tooth arrow tiller the first years and a notch disk tiller the last year were used for the tilled strip. More details of site description, plant material, orchard planting conditions, certification, maintenance, irrigation, tree training, and OFMS were previously described in Stefanelli et al. (2009). Soil sampling and measurements Soil samples were collected four times per year (April, June, August, and November) at 0–10 and 0–30 cm depth starting from April 2001 till November 2005 to measure the temporal effect on the soil conditions. Each sample was a composite obtained by mixing 20 cores from each main plot always 30 to 50 cm away from any tree trunk. The organic material (either vegetation or mulch) above soil was removed before sampling. The two depths were chosen to represent the surface soil, where most of the microbial processes take place (0–10 cm) and the most frequently explored part of soil by roots (0–30 cm). The two depths also provided an indication of the effect of depth on the soil conditions. Soil samples were stored at 4°C until the analyses were performed. Inorganic N (NO3− and NH4+) was determined by the Michigan State University (MSU) Soil and Plant Nutrient Laboratory on KCl extracts, following the procedure described by Kenney and Nelson (1982) using a Lachat-automated colorimetric analyzer (Lachat Instruments, Inc., Milwaukee, WI, USA). NO3− data were collected from 2001 to 2005, NH4+ from 2003 to 2005; consequently, total inorganic N was available only from 2003 to 2005. Organic matter content was measured by loss on ignition of 3 g of dry soil at 400°C for 8 h using a muffle furnace. Data were collected from 2001, at the time of installation of the OFMS, to 2005. Soil carbon content was calculated from the organic matter values and divided by 1.724. This value is based on organic matter containing 58% carbon, which, as reported by Stevenson (1994), can be used to obtain an acceptable estimate of C soil content.
Values obtained from the organic matter were corrected for the relative surface covered from each segment of the treatments (alley, tree row, and in case of the sandwich, vegetated area and tilled strip). Soil bulk density was estimated following the system described by Brady and Weil (2002) by which a hole was made in the plot and the soil was taken, dried, and weighed, while the hole was lined with plastic and its volume estimated by using known quantities of water. Corrected values were then related to the volume of soil, respectively, at 0–10 and 0–30 cm depth, contained in a hectare and showed as tons per hectare. Data were reported for the year 2005 and as average of the period 2002–2005 for both sampling depths (0–10 and 0–30 cm). Carbon mineralization potentials were obtained through laboratory incubation of fresh soil samples collected on April 13, 2001 and April 24, 2003. The soil samples were sieved through a 5-mm screen, and sub-samples of 50 g dry soil equivalent were weighed into 100 ml specimen containers. Moisture was adjusted to 50% of water-holding capacity which was estimated with the funnel method (Paul et al. 2001). Specimen containers were placed in mason jars with 10 ml distilled water to maintain humidity, and these were sealed with lids that had rubber septa. Jars were kept in a dark room at 25°C, and CO2 content of the headspace in the jar was determined after 21, 30, 50, 77, 100, and 150 days with an infrared gas analyzer (LI-COR, Lincoln, NE, USA) following the procedure described by Paul et al. (2001). Nitrogen mineralization potentials were determined from fresh samples of same date as C mineralization. After sieving through a 5-mm screen, sub-samples of 20 g dry soil weight equivalent were put into 100 ml specimen containers. Soil moisture of samples was adjusted to 50% of water-holding capacity estimated with the funnel method (Paul et al. 2001). Specimen containers were kept in a dark room at 25°C within a plastic box with water in the bottom to maintain humidity. One set of samples was analyzed for each time interval: 0, 30, 70, and 165 days. At the end of the respective incubation period, inorganic N (NH4+ +NO3−) was extracted with 1 M KCl and aliquots run on a Lachatautomated colorimetric analyzer (Lachat Instruments Inc., Milwaukee, WI, USA). The effect of OFMS on microbial communities was measured twice during the growing season (April and November) starting from November 2003 until April
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were significant, means were separated using least squares means (LSMEANS) test with p≤0.05. All the soil data statistical analysis was considered separately (to determine the effect on microbial populations) as well as repeated measures (to determine the overall effect on microbial dynamics). Repeated measures were performed using block×OMFS as the subject.
2005. Composition of nematode populations was utilized as an indicator of soil functionality and biodiversity (Yeates 2003) since it reflects the soil and ecological processes (Yeates 1999). Being predators, the relative nematode populations’ abundance in soil will reflect the relative biological composition of the soil on which they predate. After collection, soil samples were transported to the soil nematode analysis facility of Dr. George Bird at MSU in East Lansing, MI, USA. The extraction of nematodes from the soil was performed by centrifugal flotation (Jenkens 1964). Nematodes were then sequentially sieved into a counting plate and identified at ×50 magnification to families, genera, and trophic group levels. Nematode communities’ composition was calculated as a percentage of each feeding group of the total number of nematodes in the soil (Bird, personal communication, 2006).
Results Soil organic matter content Prior to the establishment of the OFMS, soil analysis showed no differences of organic matter content between plots with a value of 1.8% (Fig. 1). Treatment and time each had significant main factor effects, and there was significant time ×treatment interaction effect. In 2002, all treatments showed an increase in SOM that did not persist in the following years. Overall, SOM increased in MU-treated plots, and by 2005, it had almost doubled (Fig. 1). Both SVA and STS increased to a lesser extent. In the case of FL, the SOM levels at the end of the experiment were the same as in the beginning. In 2002, STS had significantly less SOM than the other treatments. At 0– 30 cm, MU had the greatest SOM overall with less differences between treatments (Fig. 2). By 2005, STS
Experimental design and statistical analysis The experiment had a completely randomized splitplot design, with six replicates. The plots consisted of 12 trees to which the main factor, ground floor management, was randomly assigned; subplots were formed by four trees (the two central were the data trees) of each of three rootstocks under test. Analysis of variance was performed using MIXED procedure with SAS (Version 8, SAS Institute, Cary, NC, USA) to detect treatment effects. When treatment effects
Percentage Organic Matter
3.5
a a
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bc ns
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ab 2.5
ab
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c
1.5 1.0 0.5 0.0 2001
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Year of soil sampling FL
Fig. 1 Evolution of content of soil organic matter in the tree row position (expressed as percent dry weight) by sampling year, for 0–10 cm depth. Each point represents a mean of six replicates (±SE) and is average of four sampling dates per year. Analysis of variance was carried out among treatments within
MU
SVA
STS
each date. Values with the same letter are not significantly different for p≤0.05 (LSMEANS test); ns not significant. FL flame burning, MU alfalfa hay mulch, SVA Swiss sandwich system vegetated area, STS Swiss sandwich system tilled strip
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Percenatge Organic Matter
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Fig. 2 Evolution of content of soil organic matter in the tree row position (expressed as percent dry weight) by sampling year, for 0–30 cm depth. Each point represents a mean of six replicates (±SE) and is average of four sampling dates per year. Analysis of variance was carried out among treatments within
each date. Values with the same letter are not significantly different for p≤0.05 (LSMEANS test). FL flame burning, MU alfalfa hay mulch, SVA Swiss sandwich system vegetated area, STS Swiss sandwich system tilled strip
had showed the greatest increase compared to initial reading. At 0–10 cm, carbon soil content was the highest with MU and the lowest with FL while SSS did not differ from either (Table 1). The amount of carbon stored in 2005 was not different from the average of the evaluation period at 0–10 cm depth (Table 1). At 0–30 cm, FL showed significantly less carbon content in soil. No differences were measured in the average 2002–2005 between the treatments (Table 1). However, both MU and SSS treatments presented an increase in stored carbon during 2005 when compared with the average 2002–2005 (Table 1).
beginning of the experiment in 2001 (data not shown). The values of cumulative milligrams of CO2-C evolved per kilogram of soil during 155 days in 2003 (Fig. 5) showed that the soil from MU had a higher accumulation of CO2, followed by the SSS, which did not differ significantly, and FL with a value significantly smaller than MU.
Soil nitrogen content MU increased soil NO3−-N at both 0–10 and 0–30 cm compared to other treatments (Fig. 3a, b). In 2002, MU increased soil NO3−-N to greater extent than other years. Nitrate and ammonium N measured from 2003 to 2005 followed the same pattern of NO3−-N with MU having the highest content between treatments for the duration of the experiment. Content of all treatments showed a significant increase in 2005, mostly due to the levels of NH4+-N (Fig. 4).
Nitrogen mineralization potential At the beginning of the experiment, the amount of nitrogen that potentially could be mineralized did not differ among treatments or location in the plots. In 2003, MU treatment had higher values of N potential than SSS and FL for all periods of incubation. After 165 days of incubation, MU had higher N mineralization potential than FL but was not significantly different from SSS (Fig. 6). Looking at the evolution during the experiment the values of N mineralization of the alley position did not have a substantial change from 2001 to 2003 for any of the OFMS, but for the row position of FL and SSS, it went to less than half of the original value. Effect on nematode community structure
Carbon mineralization potential
Effect of the OFMS
The OFMS had an effect on C mineralization potential. There were no differences between plots at the
Nematode community structure was affected by the treatments during the 18 months of the experiment
Author's personal copy Org. Agr. Table 1 Tons of carbon contained in 1 ha of soil covered with each treatment for 2005 and as annual average of the period 2002–2005
OFMS
Depth 0–10 cm
Depth 0–30 cm
2005
2005
Average 2002–2005
(November 2003–April 2005). MU showed the highest number of total nematodes between the treatments. Bacterivores represented the highest percentage in the community structure in all the treatments followed by the fungivores, except for SVA where herbivores presented the same percentage as the fungivores (Table 2). However, between the treatments, some differences in the structure composition were noted. While MU presented the highest percentage of bacterivores between the treatments, FL and STS presented the highest percentage of fungivores and omnivores, and SVA presented the highest percentage of herbivores (Table 2). No differences were noted between treatments for the carnivores. Mulched soil presented the lowest percentage of herbivores. The number of lesion nematodes in the apple roots was the lowest under MU (Fig. 7).
Average 2002–2005
FL
18 b A
18 b A
46 b A
44 a A
MU
22 a A
21 a A
51 a A
47 a B
SSS
20 ab A
19 ab A
51 a A
45 a B
Different small letters represent statistical difference (LSMEANS with p≤0.05) between the treatments inside of the years (letters should be read vertically). Different capital letters represent statistical difference (from orthogonal contrasts at p≤0.05) between the years inside of each treatment (letters should be read horizontally) OFMS orchard floor management system, FL flame burning, MU alfalfa hay mulch, SSS Swiss sandwich system
A 80 a
NO3 - N (mg/kg)
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0 2001
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Treatments FL
MU
SVA
STS
B
NO3 - N (mg/kg)
Fig. 3 Content of NO3−-N in soil for row position (expressed as milligrams per kilogram) by sampling date. a For 0–10 cm depth. b For 0–30 cm depth. Each point represents a mean of six samples and average of two dates per year (±SE). Analysis of variance was carried out for each date. Values with the same letter are not significantly different for p≤0.05 (LSMEANS test). FL flame burning, MU alfalfa hay mulch, SVA Swiss sandwich system vegetated area, STS Swiss sandwich system tilled strip
50 45 40 35 30 25 20 15 10 5 0
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2005
Author's personal copy NO3-N + NH4-N in mg/kg
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40
a
30 20
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b
b
b
b
b b
10
b
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0 2003
2004
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Year FL
MU
SVA
STS
Fig. 4 Content of total mineral N in soil for row position in 0–30 cm depth (expressed as milligrams per kilogram of NO3−N+NH4+-N) by sampling year. Each point represents a mean of six samples and average of two dates per year (±SE). Analysis of variance was carried out for each date. Values with the same
letter are not significantly different for p≤0.05 (LSMEANS test). FL flame burning, MU alfalfa hay mulch, SVA Swiss sandwich system vegetated area, STS Swiss sandwich system tilled strip
Temporal effect
period (Fig. 8). MU had the lowest percentage of fungivores in November 2003 and April 2005 and the highest percentage of bacterivores for the entire period (Fig. 8). There was a temporal effect on the community structure inside of each treatment. In all of them, the total number of nematodes increased in time, except for STS, where it remained constant (Table 3). All the treatments showed an increase in bacterivores for the duration of the experiment, except for STS where there was a decrease (Fig. 9). Also the relative abundance of the different feeding groups changed between treatments. In FL, the herbivores diminished; in MU, herbivores and fungivores diminished; and in SVA, there was not a clear variation. In STS, with the diminishing of the bacterivores, there was an increase of fungivores. Omnivores and carnivores did not seem affected by temporal variation during the experiment period (Fig. 9).
At each collecting date, the nematode community structure followed the general rule shown in Table 2. With some exceptions, SVA always presented the highest number of herbivores during the experiment 1400
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Days of incubation mulch
sandwich
Soil moisture content flame
Fig. 5 Carbon mineralization. Cumulative milligrams of CO2-C evolved per kilogram of soil during 155 days of laboratory incubation at 25°C and no light for soil from row position of three orchard floor management systems. Samples were collected on April 24, 2003. Analysis of variance was carried out for each period of incubation. Values with the same letter are not significantly different for p≤0.05 (LSMEANS test). ns no significant difference, FL flame burning, MU alfalfa hay mulch, SVA Swiss sandwich system vegetated area
Measurements performed with TDR to the depth of 45 cm showed that MU and FL had significant higher soil moisture than SSS during part of the season of 2002. From 2003 onward, there were no significant differences between the treatments even though the tendency of lower values for SSS was the same as in the previous year as reported by Stefanelli et al. (2009).
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mg (NO3-N + NH4-N).kg-1
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Fig. 6 Nitrogen mineralization potential. Nitrogen available in soil (milligrams per kilogram) after different days of incubation in laboratory at 25°C and no light from soil of the row position (0–10 cm depth) from different treatments. Each value is a mean of six samples. Samples were collected on April 24, 2003.
Analysis of variance was carried out for each period of incubation. Values with the same letter are not significantly different for p≤0.05 (LSMEANS test). FL flame burning, MU alfalfa hay mulch, SVA Swiss sandwich system vegetated area
Discussion
alleyways where the treatments remained unchanged and where vegetation was mowed and left on site. The three orchard management systems focused on an area down the tree rows, which was approximately 1.5–2.0 m in width, where they made the greatest impact. The amount of material added through the mulching process to the row generated an expected (Merwin et al. 1994; Sanchez et al. 2003) increase of SOM (Fig. 1) especially in the first layer of soil
The OFMS made significant impacts on soil condition. The change in amount of organic matter in soil is a slow process that takes years unless large quantities are added. The increase of SOM measured in 2002 reflected the high input from the cover crops and green manure previous to plantation of fruit trees. Organic matter content did not change through the years in the
Table 2 Nematode community structure during the 18 months of the experiment (average of four sampling dates between November 2003 and April 2005) at 0–30 cm depth expressed as percentage of each feeding group based on the absolute nematode density OFMS Feeding behavior Herbivores
FL
MU
STS
3c
14 a
5 bc
Fungivores
18 a
9c
14 b
21 a
Omnivores
5a
3b
4 ab
5a
Carnivores
1a
1a
1a
1a
68 b
84 a
67 b
68 b
471 c
1246 a
754 b
343 c
Bacterivores Absolute nematode density
8b
SVA
Different letters represent statistical difference (LSMEANS with p≤0.05) between the treatments inside of each nematode feeding behavior and should be read horizontally OFMS orchard floor management system, FL flame burning, MU alfalfa hay mulch, SVA Swiss sandwich system vegetated area, STS Swiss sandwich system tilled strip, Absolute nematode density total nematodes number per gram of soil
Author's personal copy Number of Nematodes/g root
Org. Agr. 25
a
a
Sandwich Row
Sandwich Strip
a
20 15
10 5
b
0 Flame
Mulch
Treatments
Fig. 7 Number of root lesion nematodes in 1 g of apple roots collected in August 2005. Different letters represent statistical difference (LSMEANS with p≤0.05) between the treatments. Bars represent standard errors. Flame flame burning, Mulch alfalfa hay mulch, Sandwich row Swiss sandwich system vegetated area, Sandwich strip Swiss sandwich system tilled strip
(0–10 cm) for MU. It is reasonable that differences for 0–30 cm were less noticeable or will take longer to be measurable, since most of that soil was not disturbed and the mulch was just placed on the soil surface, but it still followed the same trend. Some of the results were surprising, considering that management effects are not normally impacted at a significant level after at least 10 years have elapsed (Díaz Rossello 1992a; Paul et al. 2001). In SVA, the dry matter produced by the cover kept the SOM at a relatively constant level and with a tendency to increase. However, the SOM content, at 0–10 cm depth, tended to decrease in the FL but stabilized in the STS above the initial value of the beginning of the experiment. It has been established that tilling increases soil aeration and loss of organic matter (Brady and Weil 2002) including its oxidation as well as movement to deeper depths in the profile. In any case, it is critical to consider that the importance of those changes will depend on the original state of the soil prior to disruption (Calderón et al. 2000). In this study, tillage reduced SOM during the first period of the experiment which then stabilized during the last 3 years. In the case of FL, burning of the organic matter and keeping the vegetated free area would explain the SOM initial reduction and diminishing trend of the following years. The initial values of NO3−-N in soil for April 2001 showed no difference between the treatment plots where the contrasting OFMS would be established.
After installation, the treatments impacted on soil condition and differences appeared in June 2001. From then on, the MU maintained higher levels of NO3−-N and NH4+-N in soil due to the continuous decomposition and mineralization of the alfalfa hay (Cookson et al. 2002). As it was expected (Donahue et al. 1971; Sarrantonio 2003), the high content in protein and N of alfalfa assured a good supply of this critical nutrient. The alfalfa hay mulch provided more organic matter, and it was efficient in conserving soil moisture through the growing season consistent with other numerous reports (Hogue and Neilsen 1987; Langord 1937; Stefanelli et al. 2009) generating an almost constant mineralization process. Apple trees absorb N under both forms: NO3− and NH4+. There are no conclusive studies about the preference for one or other in their nutrition, and it is generally accepted that the best is a combination of both forms. The importance of NO3− or NH4+ varies with the relative availability of the two forms which has to do with soil characteristics and environmental conditions that influence microbial populations capable of carrying out ammonification and nitrification processes. Values in 2005 of NH4+-N increased greatly due to climatic conditions but kept the same relationship among treatments without modifying their relative impact. Organic matter is mostly responsible for the carbon sequestration and storage in the soil. When we projected the treatments as if applied to the entire surface of an orchard to estimate the total carbon stored, we did not find the same differences reported for the SOM in each single segment. At 0–10 cm depth, MU is still storing the highest amount of carbon per ha, FL the least, and SSS is in the middle. Since the values of year 2005 do not differ from the average of the period (Table 1), it tells that changes over the years, if any, after the first impact due to the application of the new OFMS are occurring at slower rates. At 0–30 cm depth, MU and SSS contained a comparable and the highest amounts of carbon, increasing during the experiment while for FL it decreased. We speculate that the impact of treatments takes more time to reach the depth of 30 cm, and thus, differences appear later giving significance to the change in 2005 compared to the average 2002–2005 (Table 1). Remembering that MU is the only treatment with continuous addition of external sources of carbon brought from other fields, it appears that the SSS is the treatment with the highest potential of storing locally more carbon in
Author's personal copy Org. Agr.
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sandwich strip b
November-2004
b b
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sandwich row mulch b
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flame
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April-2004
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mulch
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mulch b
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flame
November-2003
Fig. 8 Treatment effect on the nematode community structure (0–30 cm) during the 18 months of the experiment (November 2003– April 2005). Feeding behaviors (expressed in the legend) are the percentage of each group based on the absolute nematode density (total nematodes number per gram of soil). Different letters represent statistical difference (LSMEANS with p≤0.05) between treatments inside each collection date. If there are no letters means no statistical difference. Flame flame burning, Mulch alfalfa hay mulch, Sandwich row Swiss sandwich system vegetated area, Sandwich strip Swiss sandwich system tilled strip
bc
b
a
a a
a
0% herbivores
the soil and thus with an important advantage from the point of view of environmental sustainability. The mineralization potential of the soil determined through incubation confirmed the impact of the OFMS. The active C pool was enhanced and followed a similar pattern to content of SOM. The OFMS, even in the case of FL, increased the active C pool compared to the values present at the time of planting the trees after many years of agriculture production under the soybean–corn rotation. The increase of SOM produced by the addition of alfalfa hay yielded an active C pool 33% higher for the MU treatment compared with FL. These results corroborate previous studies, where living ground cover (including weeds) was found to positively affect the active C pool (Hoagland et al. 2008; Sanchez et al. 2003). The herbaceous
fungivores
c
50% omnivores
carnivores
100% bacterivores
vegetation in the row of the SSS in this study made a significant contribution increasing that C pool reservoir by 13% compared with FL. The size of the active N pool was also affected by the OFMS. The importance of N held in SOM has been stated in regard to its value as a source for plant uptake (Bloksma 2000; Díaz Rossello 1992b; Powlson and Jenkinson 1990). We can estimate that N significantly increased in the MU row due to the enhanced active N pool. Quality of the organic material added on surface to the soil has an important impact on the mineralization process (Brady and Weil 2002; Handayanto et al. 1997; Wardle and Lavelle 1997). The difference of the active N pool within the SSS treatment for the different sampling positions could be caused by the
Author's personal copy Org. Agr. Table 3 Total number of nematodes per gram of soil at different dates during the 18 months of the experiment (November 2003–April 2005) at 0–30 cm depth OFMS Date of collection
FL
MU
SVA
STS
November 2003
169 b
226 c
225 c
179 a
April 2004
264 b
405 c
356 c
235 a
882 a
1,123 b
1,356 a
611 a
572 ab
3231 a
1,081 b
345 a
November 2004 April 2005
Different letters represent statistical difference (LSMEANS with p≤0.05) between the dates of collection inside of treatment and should be read vertically OFMS orchard floor management system, FL flame burning, MU alfalfa hay mulch, SVA Swiss sandwich system vegetated area, STS Swiss sandwich system tilled strip
effect of the tilling and of the diverse cover composition of row and alley. The different plant species differ in mineral uptake and generate a different type of residue for soil. The mix of legumes and grasses in the alleyway grew with little restriction, other than occasional mowing, but likely was fixing N in higher quantities than the understory in the SVA, where a higher number of grasses and broadleaf species were likely taking up more N than fixing it. The SSS treatment provided a different environment than MU or FL, with lower levels of N and slightly lower soil moisture content (Stefanelli et al. 2009). This is consistent with previous research (Hogue and Neilsen 1987) in which organic mulches were compared to permanent orchard vegetation, cultivation, and herbicide applications. Even though these treatments are not exactly the same as FL and SSS, comparable conditions could be assumed between FL and herbicide and between SSS and a mix of vegetation and cultivation. Our experiment supports previous studies (Ferris et al. 2004; Mader et al. 2002; Yao et al. 2005) confirming that OFMS has an impact on the soil biology composition that we represented by the relative abundance (percentage on the total) of nematode populations (Ferris et al. 2001; Ritz and Trudgill 1999; Sánchez et al. 2006; Yeates 2003) with different feeding habits. The total number of nematodes was the highest in MU followed by SVA. The difference between these two and the others is probably caused by the continuous decomposition of the vegetative material on the soil (Cookson et al. 2002) as well as an active and developed root mass, both of these conditions meaning the supply of adequate habitat and
abundant food resources which promote microorganism’s development. In all the treatments, the bacterivores dominated the nematode population, which was the highest in MU and had no differences between the other treatments. The composition of the remaining nematode population varied depending on the treatment. According to Ingham et al. (1985), the more stressful the environment by lacking in nutrients (N and P) and/or water, the higher will be the amount of fungal feeding nematodes. This was corroborated in our experiment, where FL and STS showed the highest number of fungal feeding nematodes, followed by SVA and MU. The number of herbivore nematodes (root feeding) in the soil is very important because of their potential to damage the crops (Merwin and Stiles 1989). The percentage of this nematode feeding population in the soil was affected by the OFMS. In fact, the SVA had the highest percentage followed by FL, STS, and MU. This result, however, was not confirmed from the number of root feeding nematodes in apple roots where FL, STS, and SVA presented the same number, with MU showing the lowest. It is not clear if the difference in percentage in the soil and the number inside the roots is due to the fact that the herbivore nematodes measured in the soil are a more diverse group than those in the roots. Another factor could be that the highest values measured in SVA could be due to the higher number of weed roots present in the treatment, since we did not measure the root feeding nematodes in the weeds. In general, the current ecological research agrees that the most beneficial food webs are those which are highly structured and diverse (Garlaschelli 2004;
Author's personal copy
Sandwich vegetated area Mulch
APRIL 05 ab
a
ab
NOVEMBER 04 ab c APRIL 04 a
a b
NOVEMBER 03 b
b
b
APRIL 05
b
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a
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ab
ab
ab
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a
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ab a
APRIL 04
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ab
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ab ab
Flame
Fig. 9 Temporal effect on the nematode community structure (0–30 cm) during the 18 months of the experiment (November 2003– April 2005). Feeding behaviors (expressed in the legend) are the percentage of each group based on the absolute nematode density (total nematodes number per gram of soil). Different letters represent statistical difference (LSMEANS with p≤0.05) between collection dates inside of each treatment. If there are no letters means no statistical difference. Flame flame burning, Mulch alfalfa hay mulch, Sandwich row Swiss sandwich system vegetated area, Sandwich strip Swiss sandwich system tilled strip
Sandwich tilled strip
Org. Agr.
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a
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a
ab b b
a ab
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0% herbivores
Paine 1996; Power 1992; Sugihara et al. 1997). Based on spatial trends and through the evolution of the populations’ diversification, in this study we suggest an impact of the OFMS on soil food web structure. Populations fluctuated according to treatments. Bacterial feeder nematodes increased in FL treatment to the detriment of herbivores. In contrast, there was a decrease in herbivore nematodes in MU with no clear tendency in other populations. The fluctuation was high in SVA of all the populations, and STS showed an increase in fungal feeder nematodes with no clear tendency of other group decreasing. If we consider the last sampling date (April 2005) as an indicator of the treatments to reach a balance in their structure, it appears that MU had the highest percentage of
fungivores
c
50% omnivores
carnivores
100% bacterivores
bacterivores, STS the highest of fungivores with mulch the lowest, and that SVA had the highest percentage of herbivores. All of these results suggest that SSS (the sum of SVA and STS) presented a more balanced food web structure while on the contrary MU had the least diversified soil food web among the treatments which is a disadvantage considering sustainability of the system. The interaction between SOM, N, moisture, and food web structure created different growth environments for the plants; however, being a living interaction, trees were able to compensate for the treatment effects as shown from the lack of difference in rootstock performance regarding tree growth (Stefanelli et al. 2009). There has also been an interaction between
Author's personal copy Org. Agr.
rootstocks and OFMS regarding yield and especially yield efficiency with M.9 RN 29 having the highest in both FL and SSS (Stefanelli et al. 2009).
species that can be seeded as green manures or used to substitute the resident vegetation providing desired system services with minimal undesired effects on the fruit trees.
Conclusions
Acknowledgments We thank Tonya Wiechel, Rod Jones, Bruce Tomkins, Armando Rabuffetti, and Steven Berkheimer for their critical comments of this manuscript and Claudio Valdés, Giovambattista Sorrenti, and the Clarksville Research Station personnel for their work in the laboratory and field. This research was funded by Instituto Nacional de Investigación Agropecuaria of Uruguay and Michigan State University.
The different OFMS had an impact on the soil properties which can build into very important differences, on the long term. This study concludes that FL is the worst option, while MU and SSS show a trend of soil improvement. Nevertheless, the need for continuous additions of carbon material to the MU system undermines its capability to directly sequester high levels of carbon, and it might be a drawback, from the sustainability perspective, depending on the availability of carbon sources in the area. The high amount of nitrogen added through the alfalfa hay could have potential to leach in the soil profile; thus, the use of this material for mulching should be adjusted carefully to prevent nitrate leaching. Either by alternating or by mixing sources of hay with different N content and C/N ratio, an adequate supply of nitrogen can be reached. The different evolutions of the two strips of SSS (SVA and STS) call for a differential management of these areas that need to be adjusted. This system offers a great potential to develop useful biodiversity that needs to be addressed. The lower values of nitrogen in SSS compared to MU and with itself at the beginning of the experiment might raise concern and suggest the need to add amendments such as compost which can easily be achieved to compensate for loss and/or competition. The SSS has proven to be a viable orchard floor management strategy for organic apple production. The ease of application of this system and its versatility show advantages when compared with the other OFMS. Even though some indicators in this experiment show the need for improvement, there are numerous possibilities for adjusting the system, removing stressful conditions, and capitalizing the advantages of SSS toward sustainability. One major tool is the selection of the correct rootstock to overcome the potential negative effects of soil conditions on tree performance as already reported previously (Stefanelli et al. 2009). Another tool is the use of specific species in the vegetated tree row and tilled strip to improve soil and growth conditions. Further research is needed to select cover
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