Municipal solid waste compost (MSWC) was successfully used to revegetate and reclaim a taconite iron ore tailing site at an active mine site (Norland and Veith,.
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MUNICIPAL SOLID WASTE COMPOST (MSWC) AS A SOIL AMENDMENT IN IRRIGATED VEGETABLE PRODUCTION G. A. Clark, C. D. Stanley, D. N. Maynard ABSTRACT. A field study was conducted to evaluate the water conservation aspects for vegetable production associated with field incorporations of municipal solid waste compost (MSWC). In June 1992, MSWC was incorporated into a sandy soil as a soil amendment at the University of Florida Gulf Coast Research and Education Center, Bradenton, Florida. Drip-irrigated and subirrigated vegetable production studies were conducted during autumn 1992, spring 1993, autumn 1993, and spring 1994 seasons. Green peppers were grown during the autumn seasons and fresh market tomatoes were produced during the spring seasons. MSWC was applied at various rates in drip-irrigated and subirrigated plots. Drip irrigation was applied based on crop water use estimated from reference evapotranspiration data and crop coefficients. A fully enclosed subirrigation system was used in the subirrigated plots with the water table controlled at an average depth of 0.60 m below the soil surface. Nitrogen fertilizer was applied to each of the MSWC, drip-irrigated, and, subirrigated plots. Incorporated MSWC was still immature (based on measured C/N ratios > 30) and reduced autumn 1992 dripirrigated pepper yields and reduced plant growth. By spring 1993 the incorporated MSWC had field matured and resulted in significantly increased tomato plant size and fruit yields in the spring of 1993 and all other subsequent drip-irrigated trials. The 134 t ha–1 MSWC rate increased spring 1993 and 1994 tomato yields by 27% and 18%, respectively, and autumn 1993 peppers by 17% over the non-amended plot yields. Drip-irrigated pepper yields were not affected by irrigation rate or applied nitrogen level. While drip irrigation rate did not affect total tomato fruit yield in any of the seasons, yield of extra large tomato fruit was greater with higher levels of applied water in the spring of 1994, and the higher applied nitrogen levels increased marketable fruit yields by 13 to 14%. In general, amending a sandy soil with MSWC significantly improved plant growth and yield in drip-irrigated vegetable production. However, applied nitrogen rate in the subirrigated fields did not affect fruit yield in any of the seasons. Autumn 1992 pepper yields and spring 1994 tomato yields in the subirrigated plots were reduced by the addition of MSWC and autumn 1993 pepper yields were greater with the addition of MSWC. MSWC increased yield of extra large tomato fruit in the spring 1993 season and reduced fruit size in the autumn 1993 pepper trial, but had no statistical effect on fruit size in any of the other seasons. Therefore, the subirrigated system results were not as conclusive as the dripirrigated results. Furthermore, immature MSWC products should be incorporated into fields with sufficient maturation time prior to planting. Keywords. Compost, Microirrigation, Tomato, Pepper.
C
onservation of water resources is important in all communities, particularly in those with expanding urban sectors such as the coastal areas of Florida. While coastal Florida is a popular area for urban growth and development, the area also provides prime agricultural land for production of commercial citrus, vegetable, and floricultural crops. Many of the commercial vegetable producers have been targeted for reductions in water allocations and potential reductions in fertilizer applications. Water management districts have
Article was submitted for publication in September 1999; reviewed and approved for publication by the Soil & Water Division of ASAE in March 2000. Presented as ASAE Paper No. 98-2172. Florida Agricultural Experiment Station Journal Series No. R-07130. The authors are Gary A. Clark, ASAE Member Engineer, Professor, Department of Biological and Agricultural Engineering, Kansas State University, Manhattan, Kansas; Craig D. Stanley, Professor of Soil and Water Science, and Donald N. Maynard, Professor of Horticulture, the University of Florida Gulf Coast Research and Education Center, Bradenton, Florida. Corresponding author: Gary A. Clark, Kansas State University, Biological & Agricultural Engineering Dept., 147 Seaton Hall, Manhattan, KS 66506-2906, phone: 785.532.2909, fax: 785.532.5825, email: .
been encouraging producers to adopt more conservative irrigation systems and to switch from ditch conveyance subirrigation systems to fully enclosed subirrigation (FES) systems (Clark and Stanley, 1992) or to drip irrigation systems (Clark and Smajstrla, 1996). However, drip irrigation systems are difficult to manage for shallow rooted crops grown on sandy soils with low water holding capacities (WHC) and low cation exchange capacities (CEC). Soil amendments that increase the available water holding capacity range of the soil and/or that increase the cation exchange capacity of the soil could help ease the drip-irrigation-related water and nutrient management difficulties on these soils. Biodegradable solid wastes are generated throughout the U.S. and are a substantial component of the waste stream of materials that go to landfills. Composted municipal solid waste (MSW) materials can add organic matter to the soil which might improve the water and nutrient availability to crops, thus enhancing the plant growth and fruit production characteristics. Municipal solid waste compost (MSWC) was successfully used to revegetate and reclaim a taconite iron ore tailing site at an active mine site (Norland and Veith,
Transactions of the ASAE VOL. 43(4): 847-853
© 2000 American Society of Agricultural Engineers 0001-2351 / 00 / 4304-847
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1995). After four years of MSWC application at rates ranging from 10 to 90 Mg ha–1, plant cover improved from zero (prior to soil amendment) to over 90% cover with some of the treatment combinations. Some treatments included additional applications of granular diammonium phosphate (DAP) which improved plant growth. Municipal garbage composted with sewage sludge significantly improved tree growth (stem wood biomass and basal tree area) in a 16-year study with slash pine (Jokela et al., 1990). Compost applications ranged from 0 to 448 Mg ha–1. The highest compost rate also added considerable levels of many metals including Cu (70 kg ha–1), Fe (2060 kg ha–1), Al (2940 kg ha–1), and Cd (272 kg ha–1). However, plant tissue analysis did not reveal any biological concern in metal levels. While soil chemistry was neither reported nor analyzed in that study, Tisdell and Breslin (1995) reported that only small percentages of these elements are leachable. Potato waste compost-amended soil improved tuber yield and quality, and improved plant appearance during drought and near-drought conditions (McBurnie, 1993). However, specific data on nutrient conditions were not reported. McConnell et al. (1990) reported that composted municipal solid waste and yard trash could be used as growth substrates (potting media) for pickerel weed (an aquatic/wetlands plant species) provided that adequate levels of N, P, and K are available. Composted MSW and yard trash media significantly reduced plant, fresh weight and general growth. Combining compost media with standard potting media and using additional fertilizer improved these growth attributes. A four-year study of composted MSW applications to soils for Christmas tree production resulted in decreased soil acidity, but no significant growth effects from the addition of the MSW material (David, 1998). In the spring of 1992 the authors were asked to evaluate the water conservation aspects associated with field incorporation of municipal solid waste compost (MSWC). The work was to be performed on vegetable crop production systems. Therefore, the objectives of this study were to: 1. Evaluate the effects of incorporated municipal solid waste compost (MSWC) on fruit yield and quality of drip-irrigated and subirrigated tomato and pepper production on sandy soils. 2. Determine if incorporated MSWC could reduce the water and/or nitrogen application requirements in drip-irrigated and / o r subirrigated vegetable production systems on sandy soils.
METHODS AND MATERIALS The experimental site was located at the University of Florida’s Gulf Coast Research and Education Center, Bradenton, Florida. Soil at the site was an EauGallie fine sand (Sandy, siliceous, hyperthermic Alfic Haplaquods) with a spodic horizon at 90 cm. Municipal solid waste compost (MSWC) was received from Reuter Recycling (product name: “Earth Life”) in May 1992. Physical, chemical, and biological characteristics of the MSWC material were analyzed during the course of this study (Graetz, 1995; Eichelberger, 1994) and are summarized in tables 1 and 2. Measured wet density of the material as 848
Table 1. Physical properties and nutrient and metal concentrations of the MSWC material used in this study (Graetz, 1995; Eichelberger, 1994) Physical/Chemical Property
Value
Percent moisture (%) Water-holding capacity @ 10 kPa — (g g–1) pH Total carbon (%) Total nitrogen (%) C:N ratio Total P (µg g–1) Total Ca (µg g–1) Total Mg (µg g–1) Total K (µg g–1) Total Na (µg g–1) Total Zn (µg g–1) Total Cu (µg g–1) Total Mn (µg g–1) Total Fe (µg g–1) Total Cd (µg g–1) Total Pb (µg g–1) Total Ni (µg g–1)
28.70 1.01 7.75 31.80 0.83 38.50 1450.00 23800.00 1240.00 1290.00 1830.00 434.00 118.00 182.00 4110.00 4.00 280.00 29.00
Table 2. Concentrations of various elements from saturated water extracts* of the MSWC material used in this study (Graetz, 1995; Eichelberger, 1994) Element
Saturated Water Extract Concentration µg mL–1
NO3-N NH4-N PO4-P Total - P Ca Mg K Na Zn Cu Mn Fe Cd Pb Ni
0.12 3.37 0.10 0.64 194.00 20.00 92.00 196.00 1.13 0.32 0.04 0.84 0.00 0.01 0.05
* Saturated water extracts were obtained using a 25 g (dry wt. equivalent) sample of MSWC and followed saturated media extract procedures for “Greenhouse Growth Media” as described in Recommended Chemical Soil Test Procedures for the North Central Region, North Central Regional Pub. No. 221 (Rev.), October 1998.
delivered was 0.32 Mg m–3. This corresponds to a dry bulk density of 0.23 Mg m–3 and is very close to the bulk density of 0.22 Mg m–3 for an MSWC material from the same location used in other work (He et al., 1995). The physical properties of MSWC materials can be highly variable with moisture contents ranging from 190 to over 500 g kg–1 and bulk densities ranging from 0.22 to 0.74 Mg m–3 (He et al., 1995). Two experimental field sites were developed to study the effects of soil incorporated MSWC on drip-irrigated and subirrigated vegetable production, respectively. The drip irrigation study was designed to evaluate three combinations of applied MSWC (0, 67, and 134 t ha–1), two nitrogen fertilizer treatments (215 and 309 kg-N ha–1), and three drip irrigation treatments (0.5×, 1×, and 1.5×). The subirrigation study (water table management) was designed with two combinations of applied MSWC (0 and 135 t ha–1), and with three applied nitrogen fertilizer rates (215, 309, and 403 kg-N ha–1). Crop studies included autumn green peppers (1992 and 1993) and spring fresh TRANSACTIONS OF THE ASAE
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market tomatoes (1993 and 1994). These experimental designs included four replications of each treatment combination in a split plot design for the drip studies and in a randomized block design for the subirrigation studies. Figures 1 and 2 show example plot layouts of the drip irrigation and subirrigation studies. The irrigation studies (drip and subirrigation) were conducted on separate field sites and this research was not designed to compare irrigation systems. All drip irrigation studies used raised beds (0.15 to 0.20 m high × 0.60 m wide) that were covered with plastic mulch (1.25 mil; 0.032 mm). White plastic was used for the autumn crops to reflect solar radiation and black plastic was used for the spring crops to absorb solar radiation. The drip irrigation tube had a 0.25-mm (10-mil) wall thickness, a 30-cm emitter spacing and a nominal discharge rate of 373 L h–1 100 m–1 at the operating pressure of 69 kPa. This resulted in an equivalent application rate of 2.5 mm h–1. Drip tubing was installed approximately 25 mm deep and in the bed center for the autumn pepper crops and 10 cm off-center for the spring tomato crops. Drip irrigation
Figure 1–Example plot design for the drip-irrigated MSWC study.
Figure 2–Example plot design for the subirrigated MSWC study. VOL. 43(4): 847-853
quantities for the 1 × treatment were based on crop coefficients and calculated grass reference evapotranspiration (ETo) using data from a nearby weather station. A portion of the total fertilizer was applied preplant at 93 and 186 kg-N ha–1 for the two fertilizer rates, respectively, using an 18-0-28 (N-P2O5-K2O) granular fertilizer. Additional N and K were applied by fertigation to provide an additional 120 kg-N ha–1 to all plots using a 6-0-5 (N-P2O5-K2O) liquid fertilizer. Subirrigation studies used raised beds (0.15 to 0.20 m high × 0.81 m wide) that were covered with white plastic mulch (1.25 mil or 0.032 mm) for the autumn crops and black plastic for the spring crops. All of the fertilizer was applied preplant in a single band in the center of the bed for the pepper plants and two bands approximately 0.15 m offcenter for the tomato plants. Preplant N and K fertilizer was applied at 215, 309, and 403 kg-N ha–1 using an 18-028 (N-P2O5-K2O) granular fertilizer based on 12 346 linear meters of bed per hectare. Preplant P fertilizer was applied at 49 kg-P ha –1 to all plots and incorporated. The subirrigated blocks were 12.5 m wide and approximately 61 m long. Water was applied by two drip irrigation laterals in each subirrigated block that were buried 0.41 m deep and used as a Fully Enclosed Subirrigation (FES) system (Clark and Stanley, 1992). The water table in each block was controlled using a shallow 0.10-m-diameter well and float switch system. When the water table dropped below the set point, the irrigation system was activated until it reached the water table elevation set point. During the first week of June 1992, measured amounts of MSWC were loaded on to a dump truck and transported to specific plots in the drip-irrigated experimental plot area. Each MSWC plot contained three vegetable production beds that each received a different irrigation schedule. The MSWC was uniformly broadcast over the plots which were 15.2 m long and 4.6 m wide. The 67 and 135 t ha–1 MSWC rates resulted in surface layers of product that were approximately 3 and 6 mm thick, respectively. A tractormounted rototiller was used to incorporate the applied MSWC. In concurrence with the standard vegetable cultural practices within the region, plot areas were bedded, fertilized, fumigated with methyl bromide/chloropicrin (MC 67:33), and covered with plastic mulch on 25 August 1992 (autumn 1992 crop), 15 February 1993 (spring 1993 crop), 16 August 1993 (autumn 1993 crop), and 16 February 1994 (spring 1994 crop). The fumigation may have adversely impacted the beneficial organisms and chemistry of the compost. However, those biological and chemical measurements were not a part of this study. Pepper transplants (‘Capistrano’) were set on 8 September 1992 and on 2 September 1993 using a 0.30 m × 0.30 m plant spacing. Tomato transplants (‘Sunny’) were set on 1 March 1993 and 1 March 1994 using a single row of plants per bed with plants on a 0.60 m spacing. The drip irrigation system was operated daily for 30 to 45 min for the first 10 to 14 days after transplanting to establish the transplants. Subsequent drip irrigation applications followed a crop ETbased schedule and were adjusted approximately every two weeks. Daily drip irrigation applications occurred in multiple cycles per day (up to three). Each cycle was limited to a one-hour run time (2.5 mm) to maintain applied water within the active root zone. Subirrigated 849
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plots were established with a water table at a depth of 0.46 m below the bed surface for 10 to 14 days at which time the float switch set point was reestablished at a control depth of 0.61 m. All plots were hand harvested when fruit were mature and fruit were graded for size and quality. Forty plants per plot were sampled for the subirrigated pepper crops. Because plant stand and visual appearance were poor in the 1992 drip-irrigated pepper plots, 80 plants per plot were sampled for those yield analyses. All tomato plots used 10 plants per plot for yield and quality analysis. Autumn 1992 subirrigated peppers were harvested on 12 and 30 November, and on 14 and 21 December. Autumn 1992 drip-irrigated plots were harvested on 30 November and 14 December. Spring 1993 drip tomato plots were harvested on 27 May, and on 8 and 21 June. Subirrigated spring 1993 tomatoes were harvested on 3, 14, and 22 June. Peppers in the autumn 1993 field test were harvested four times in the drip-irrigated plots (3 and 17 November, and 1 and 15 December) and three times in the subirrigated plots (8 and 22 November, and 10 December). Tomatoes in the spring 1994 field test were harvested three times in the dripirrigated plots (19 and 27 May, and 6 June) and twice in the subirrigated plots (19 and 31 June). In addition, plant samples were collected from the autumn 1992 dripirrigated and subirrigated pepper, and from the spring 1993 tomato drip-irrigated plots for aboveground, non-fruit dry matter production.
RESULTS Rainfall, pan evaporation, and air temperature data for the autumn and spring seasons are summarized in table 3 for the autumn pepper crops and spring tomato crops. Seasonally applied drip irrigation amounts are presented in table 4. The resultant seasonal irrigation amounts do not equal the 0.5 ×, 1.0×, and 1.5× proportions because all plots were initially irrigated at the same rate for plant establishment. Autumn 1992 irrigation amounts were much Table 3. Climatic data, 1992-1994
Month
Pan Average Pan Average Rainfall Evapora- Temp. Rainfall Evapora- Temp. (mm) tion (mm) (°C) (mm) tion (mm) (°C) Autumn 1992 Pepper Crop
September 99 October 81 November 46 December 40 Season 266
March April May June Season
134 106 93 69 402
27.8 23.3 21.7 18.9 22.9
Autumn 1993 Pepper Crop 104 180 17 25 310
138 95 69 72 374
27.8 25.6 21.1 16.7 22.8
Spring 1993 Tomato Crop
Spring 1994 Tomato Crop
59 110 39 93 301
71 65 5 274 276
110 143 173 181 607
19.4 20.0 23.9 27.8 22.8
120 148 174 159 601
20.6 23.9 24.4 27.8 24.2
Table 4. Drip irrigation application amounts Irrigation Autumn 1992 Treatment (mm) 0.5× 1.0 × 1.5×
850
38 53 97
Spring 1993 (mm) 107 132 201
Autumn 1993 Spring 1994 (mm) (mm) 114 191 264
53 89 127
lower than those used in autumn 1993 even though 1992 rainfall was lower and pan evaporation rates were higher. These differences were due to a poor plant stand and small plant size that occurred with the autumn 1992 pepper crop. In addition, November and December 1993 rain was low when plant size and subsequent water demand was greatest. Substantial rainfall during June 1994 reduced drip irrigation amounts during that peak growth period of the plants and resulted in lower seasonal drip irrigation applications than used in the spring of 1993. With a plastic mulch bed culture, it is difficult to estimate effective rainfall. Many small rainfall events are not effective at all and typically have to be disregarded with respect to the irrigation schedule. Plot tensiometers were used to assess root zone soil water contents and were subsequently used to adjust irrigation schedules. Observations of the MSWC indicated several problems, including crushed glass (> 6 mm diameter), pieces of plastic, and an odor due to incomplete composting. Bengtson and Cornette (1973) reported that while applied MSWC to a young slash pine site did not adversely affect soil or trees, aesthetics of the site were degraded by the residue of nondegradable particulates. Soil samples were obtained in July of 1992 and 1993 from the study site for physical analysis and to develop the pressure potential/water content relationship (Turner et al., 1994). Dry bulk density of the surface soil decreased linearly with the addition of MSWC and in 1993 ranged from 1.39 g cm–3 to 1.31 g cm–3 for the 0 and 135 t ha–1 MSWC treatments, respectively. Addition of MSWC increased the water content of the soil at all soil water tensions between 5.0 and 100 kPa. However, the shape of the water content/soil water tension relationship was the same for all soils. Thus, the amount of water released between any two specific soil water tensions was not different for any of the MSWC soil amendment levels. Additional details of the soil physical analysis can be found in Turner et al. (1994). Throughout the autumn 1992 season, drip-irrigated pepper plots showed visual signs of plant stress (pale green leaves and reduced growth) which appeared to be related to the availability of N fertilizer. The carbon and nitrogen ratio (C/N) of the compost source material was 38.5 (Graetz, 1995) and was designated as immature based on a maturity C/N threshold of 30 or less, thus indicating a nitrogen demanding product. Similar effects were reported by Bengtson and Cornette (1973) and McConnell et al. (1990). However, autumn 1992 subirrigated pepper plants did not visually show the same stress symptoms. Plant samples from both irrigation treatments were collected and measured for aboveground dry matter production to ascertain relative sizes (table 5). These data are provided to indicate the relative differences associated with the two irrigation systems during the initial phase of this work. Drip-irrigated pepper plants were not significantly affected by drip irrigation rate or applied nitrogen level. However, plant sizes were highly variable and the higher nitrogen plots had a trend toward larger plants. Application of MSWC significantly reduced both drip irrigated and subirrigated pepper plant size, thus supporting the possibility of a nitrogen demanding system. In addition, all drip-irrigated plants developed only 20% of the aboveground biomass that the subirrigated plants had developed. This difference was probably due to the TRANSACTIONS OF THE ASAE
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Table 5. Main effects of irrigation, nitrogen, and MSWC on aboveground plant dry matter results for the autumn 1992 drip-irrigated and subirrigated peppers, and the spring 1993 drip-irrigated tomatoes Autumn 1992 Pepper Dry Matter† (g plant–1)
Main Effect
Spring 1993 Tomato Dry Matter (g plant–1)
Irrigation 0.5 × 1.0 × 1.5 × Significance‡
Drip Irrigated 1.59 1.77 1.68 ns
Subirrigated -
Drip Irrigated 340 368 360 ns
Nitrogen 215 kg ha–1 309 kg ha–1 403 kg ha–1 Significance
1.59 1.73 ns
7.26 9.08 8.17 ns
343 369 **
MSWC 0 t ha–1 7 t ha–1 134 t ha–1 Significance
1.86 1.50 1.63 *
9.99 8.63 **
278 385 405 ***
† These results are provided to indicate the differences associated with the different irrigation systems during start-up of this project. ‡ Level of statistical significance is indicated at the 10% (*), 5% (**), 1% (***) levels or not significant (ns).
establishment of the transplants and overall drip irrigation water management during that first season. The characteristics of a subirrigated field result in wetter field soil conditions which could have enhanced the MSWC “maturing” processes in that field. Due to the water application characteristics of drip irrigation, that field was noticeably drier in the row middles. At final harvest neither irrigation nor fertilizer rate had any effect on drip-irrigated pepper yield (table 6) or fruit size (table 7). Measured drip-irrigated yield reductions during the autumn 1992 season occurred with increased MSWC rates (table 6). These yield reductions were attributed to the nitrogen demand by the MSWC. However, MSWC rate did not significantly affect fruit size. By the spring 1993, the soil microflora may have recovered from fumigation and the compost must have field matured. Drip-irrigated tomato plant sizes (table 5) Table 6. Main effects of irrigation, nitrogen, and MSWC on marketable fruit yield for the autumn 1992 and 1993 drip-irrigated peppers, and the spring 1993 and 1994 drip-irrigated tomatoes Marketable Fruit Weight (Mg ha–1)
Main Effect Irrigation
Autumn 1992 Spring 1993 Autumn 1993 Spring 1994 Peppers Tomatoes Peppers Tomatoes
0.5× 1.0× 1.5× Significance
16.0 16.2 15.7 ns
72.3 76.1 75.6 ns
33.0 34.2 30.6 ns
103.8 108.2 103.0 ns
Nitrogen 215 kg ha–1 309 kg ha–1 Significance
15.3 16.6 ns
70.0 79.3 ***
32.5 32.7 ns
98.0 112.0 ***
MSWC 0 t ha–1 67 t ha–1 134 t ha–1 Significance
17.2 15.9 14.8 *
64.4 77.8 81.8 ***
29.5 33.7 34.6 ***
94.3 109.5 111.3 ***
Level of statistical significance is indicated at the 10% (*), 5% (**), 1% (***) levels or not significant (ns). VOL. 43(4): 847-853
Table 7. Main effects of irrigation, nitrogen, and MSWC on average fruit size for the autumn 1992 and 1993 drip-irrigated peppers, and on yield of extra large fruit for the spring 1993 and 1994 drip-irrigated tomatoes Average Fruit Size (peppers) and Extra Large Fruit (tomatoes)
Main Effect
Irrigation
Autumn 1992 Spring 1993 Autumn 1993 Spring 1994 Peppers Tomatoes Peppers Tomatoes (g fruit–1) (Mg ha–1) (g fruit–1) (Mg ha–1)
0.5× 1.0× 1.5× Significance
184 187 179 ns
29.7 30.3 33.2 ns
153 151 153 ns
20.7 25.0 26.9 **
Nitrogen 215 kg ha–1 309 kg ha–1 Significance
179 184 ns
30.8 31.4 ns
151 153 ns
23.0 25.3 ns
MSWC 0 t ha–1 67 t ha–1 134 t ha–1 Significance
187 184 179 ns
22.7 35.2 35.4 ***
151 155 153 ns
17.2 24.9 30.4 ***
Level of statistical significance is indicated at the 10% (*), 5% (**), 1% (***) levels or not significant (ns).
and yields (table 6) were significantly larger with increased levels of applied MSWC as well as with increased applied nitrogen. Marketable yields of drip-irrigated fruits from the spring 1993, autumn 1993, and spring 1994 field studies were not significantly affected by irrigation rate. Thus, applied water was not a substantial yield factor in this study. However, drip-irrigated tomato yields from both spring studies were significantly increased with additional nitrogen. Furthermore, the addition of MSWC significantly increased total fruit yields of drip-irrigated tomatoes and peppers during the last three seasons of this study. These data suggest that the MSWC had field matured during the autumn 1992 season, thus resulting in the yield and growth benefits measured during the subsequent seasons. It is possible that the matured MSWC improved the cation exchange capacity (CEC) of the soil, thus providing more nutrient exchange sites for the plants to access (Hanlon, 1993). However, these measurements were not conducted in this work. Average fruit size of drip-irrigated peppers and yield of extra large tomatoes were not affected by nitrogen rate in any of the study seasons (table 7). However, irrigation rate increased yield of extra large tomato fruits in the spring of 1994, but had no effect on pepper fruit size or extra large tomato fruit yield during any of the earlier seasons. The spring 1994 season was relatively dry during May when fruits typically increase in size. Thus, the reduced water treatments may have been slightly stressed resulting in fewer extra large fruit. Addition of MSWC did not affect the average size of drip irrigated peppers in 1992 or 1993. However, yield of extra large tomato fruits (1993 and 1994) in the drip-irrigated studies was significantly increased by the addition of MSWC. Applied nitrogen level did not significantly affect yield or fruit size in the subirrigated study during any of the seasons (tables 8 and 9). Results of applied MSWC in the subirrigated plots resulted in reduced pepper and tomato fruit yields in the autumn 1992 and spring 1994 seasons, respectively (table 8). However, applied MSWC resulted in 851
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Table 8. Main effects of nitrogen and applied MSWC on yield of marketable fruit from autumn 1992 and 1993 peppers, and spring 1993 and 1994 tomatoes in the subirrigated plots Marketable Fruit Weight (Mg ha–1)
Main Effect Irrigation
Autumn 1992 Spring 1993 Autumn 1993 Spring 1994 Peppers Tomatoes Peppers Tomatoes
Nitrogen 215 kg ha–1 309 kg ha–1 403 kg ha–1 Significance
33.1 33.4 34.9 ns
68.1 74.1 75.9 ns
31.2 34.7 34.6 ns
85.5 85.1 83.9 ns
MSWC 0 t ha–1 134 t ha–1 Significance
36.1 32.8 **
73.9 71.5 ns
31.1 35.8 **
89.4 80.3 **
Level of statistical significance is indicated at the 10% (*), 5% (**), 1% (***) levels or not significant (ns). Table 9. Main effects of nitrogen and applied MSWC on average fruit size of autumn 1992 and 1993 peppers, and yield of extra large fruit from spring 1993 and 1994 tomatoes in the subirrigated plots Average Fruit Size (peppers) and Extra Large Fruit (tomatoes)
Main Effect
Irrigation
Autumn 1992 Spring 1993 Autumn 1993 Spring 1994 Peppers Tomatoes Peppers Tomatoes (g fruit–1) (Mg ha–1) (g fruit–1) (Mg ha–1)
Nitrogen 215 kg ha–1 309 kg ha–1 403 kg ha–1 Significance
187 184 187 ns
23.3 24.5 30.2 ns
165 174 167 ns
41.5 45.5 45.7 ns
MSWC 0 t ha–1 134 t ha–1 Significance
190 184 ns
22.6 29.4 **
172 165 *
44.9 43.5 ns
Level of statistical significance is indicated at the 10% (*), 5% (**), 1% (***) levels or not significant (ns).
increased yield of extra large tomato fruit in the spring 1993 season (table 9) and greater pepper yields in the autumn 1993 season (table 8). While the subirrigated MSWC tomato plot yields were lower than yields from non-amended plots (table 8), plants in subirrigated MSWC plots looked larger and greener and may have had more vegetative growth and less reproductive growth. While this study was not designed to statistically compare drip irrigation with subirrigation, some relative comparisons can be made. Drip-irrigated pepper yields were substantially lower and approximately one-half of the magnitude of the subirrigated yields in the autumn 1992 season. All drip-irrigated plots were affected, indicating that plot water management may have been a factor in that initial season. All drip irrigated plants in 1992 appeared to be nitrogen deficient. This was not a problem during subsequent seasons and drip-irrigated tomato yields were consistently higher than subirrigated tomato yields (tables 6 and 8). Fruit size differences between drip-irrigated and subirrigated plots were not consistent. The spring 1993 extra large tomato yield was slightly lower in subirrigated plots than drip-irrigated plots (tables 7 and 9). However, spring 1994 subirrigated extra large fruit yield was greater than drip-irrigated extra large fruit yield.
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SUMMARY AND CONCLUSIONS In general, field applications of immature MSWC reduced nitrogen availability and reduced growth and yield of fresh market green peppers in both drip-irrigated and subirrigated autumn 1992 experiments. However, fresh market tomato and green pepper yields, and yield of extra large tomato fruits increased with applied MSWC rate in subsequent seasons (spring and autumn 1993, and spring 1994) on sandy soils amended with MSWC and irrigated by drip irrigation. Pepper fruit yields on subirrigated plots amended with MSWC were greater than non-amended plot yields in the autumn 1993 field study. However, tomato fruit yields were lower in MSWC plots than non-amended plots in the spring 1994 study. Similar results were reported by Obreza and Reeder (1994) with initially reduced tomato yields followed by increased watermelon yields on MSWC amended plots. The addition of 67 and 134 t ha–1 of MSWC resulted in drip-irrigated tomato yield increases of 21 and 28%, respectively, in spring 1993, and increases of 16 and 18%, respectively, in the spring 1994. The yield increases from the 0 to the 135 t ha–1 MSWC applications averaged 17 Mg ha–1 of marketable tomato fruit. With an average market price of $10/11.3 kg box of fruit, this represents a market value increase of $15,000/ha–1. Most of the MSWC related yield increase in the 1993 tomatoes (table 5) was in the extra large fruit class (table 5). The extra large fruits can bring a market price of $150 to $250 Mg–1 higher than the large size fruits. Therefore, increases in the extra large fruit yield associated with the addition of MSWC could represent a $2,500/ha–1 financial advantage just based on fruit size alone. Incorporation of MSWC into sandy soils for dripirrigated vegetable production provided improved plant growth and yield. However, the incorporated MSWC must be mature prior to cropping. Immature product should be incorporated into field soils four to six months prior to planting to provide time for field maturation. Additional work should focus on the soil fertility, biological, and cation exchange capacity characteristics of MSWC amended soils.
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