Springer 2006
Plant and Soil (2006) 279:95–105 DOI 10.1007/s11104-005-0436-3
Effect of zero tillage and residues conservation on continuous maize cropping in a subtropical environment (Mexico) P. Monneveux1,3, E. Quille´rou2, C. Sanchez1 & J. Lopez-Cesati1 1
CIMMYT, A.P. 6-641, 06600, Mexico D.F, Me´xico. 2Ecole Nationale Supe´rieure Agronomique de Montpellier, 34070, Montpellier Cedex 01, France. 3Corresponding author*
Received 7 January 2005. Accepted in revised form 30 June 2005
Key words: Canavalia ensiformis L., intercropping, residue conservation, Zea mays L., zero tillage
Abstract The effects of zero tillage and residue conservation in continuous maize-cropping systems are poorly documented, especially in the tropics, and are expected to vary highly with climatic conditions and nitrogen availability. In the present study, maize was cultivated during the wet and dry seasons in central Mexico for three consecutive years, under different treatments combining tillage with residue management techniques and with nitrogen rates. In some treatments, maize was also intercropped with jackbean, Canavalia ensiformis L. (DC). Yield and yield components as well as physiological traits and soil characteristics were assessed during the wet and dry seasons for the third year of cultivation. During the wet season, zero tillage was associated with less biomass and grain yield. Leaf chlorophyll concentration was smaller under zero tillage, suggesting less nitrogen uptake. Both zero tillage and residue conservation reduced early growth and strongly increased ear rot. During the dry season, zero tillage was associated with greater root mass, as measured by electrical capacitance. Residue conservation decreased the anthesis-silking interval, suggesting better water uptake. There was, however, no significant effect of tillage or residue management practices on yield. Zero tillage was found to be associated with increased soil bulk density, nitrogen concentration and microbial biomass organic carbon. Residue conservation increased soil carbon concentration as well as microbial biomass organic carbon. Intercropping with jackbean and conservation of its residues in addition to maize residues increased soil nitrogen concentration. Further investigation may provide more information on the factors related to zero tillage and residue conservation that affect maize early growth, and determine to which extent the observed modifications of soil chemical and physical properties induced by conservation tillage will further affect maize yield.
Introduction Conservation agriculture (CA) techniques have been developed to reduce the negative environmental effects of agriculture such as soil degradation of physical properties and soil erosion, leading to decreased productivity. CA techniques involve zero tillage, conservation of residues, and optimal rotation or association of crops (Smart and Bradford, 1999). * E-mail:
[email protected]
In zero tillage, soil preparation is minimal, only enough to bury the seed. Zero tillage has been practiced since the beginning of agriculture until the invention of animal-drawn ploughs. However, zero tillage with scientific bases, as an alternative to conventional tillage, began in the 1940s with the discovery of hormonal herbicides that allow farmers to control weeds without resorting to cultivators or hoes. Nowadays, there are approximately 90 million hectares worldwide under zero tillage (Derpsch, 2003). Zero tillage increases the mechanical resistance and the
96 apparent density of soil and curbs the soil evaporation rate (Rivas et al., 1998). Water infiltration and soil aeration that depend on bulk density are also modified (Rice et al., 1987). Zero tillage affects water availability to plants, essentially through soil water capture and root uptake capacity (Gajri et al., 1994; Ojeniyi, 1986). Zero tillage has also been reported to increase total nitrogen and microbial biomass in various soils (McCarty et al., 1995). Moreover, zero tillage reduces the number of field operations reducing input costs for labour, fuel, tractors, and other equipment (Raper et al., 1994). Zero tillage generally results in greater economic returns, compared with conventional tillage system, due to both greater yields in dry years and smaller production costs in all years (Smart and Bradford, 1999). Residue conservation represents a package of practices that leaves at least 30% of crop residues on the surface at planting (Jourdain et al., 2001). These crop residues constitute a mulch cover that protects the soil against run-off and erosion (Perret et al., 1999) and increases the percentage of organic matter in the superficial soil layer (Rivas et al., 1998; Roldan et al., 2003). Nutrient loss due to runoff is also decreased (Smart and Bradford, 1999). The capacity of the soil surface to intercept rainfall is improved because of changes in soil roughness, soil surface porosity and hydraulic conductivity of the topsoil. Mulching also reduces temperature extremes (Radford et al., 1995; Shinners et al., 1994) and direct evaporation (Liu et al., 2000; Steiner, 1989). Conservation tillage, defined as the combination of zero tillage and residue conservation (Violicˇ, 1998) shows considerable potential for stabilizing production in semi-arid areas. It often leads to an increase in grain yield as a result of improved water, carbon and nitrogen resources (Husnjak et al., 2002; Lal, 1995). Economic returns of conservation tillage can be substantially increased by the use of rotation or intercropping that break soil pathogen cycles and reduce weed pressure (Bailey, 1996). The development of intercropping cultivation of feed or food legumes is considered as a factor for successful widespread use of CA in maize-based systems (Buckles and Barreto, 1996). In addition to fixing nitrogen, legume green manures provide ground cover that reduces soil erosion, facilitates weed control and
may alleviate compaction in intensely cultivated soils (Osei-Bonsu et al., 1996). When intercropped with maize, the legume green manures may be chosen in relation to its adaptation to its environment, degree of concurrence with maize, tolerance to shading and production of biomass and nitrogen per hectare. Today CA is practiced mainly by large-scale, commercial farmers worldwide (Ekboir, 2002). In Latin America, CA techniques developed in this socio-economic context have often been indiscriminately proposed to farmers (Erenstein, 1996). In Mexico, CA techniques are poorly developed (Jourdain et al., 2001). The main limiting factor for the development of CA techniques is the poor diversification of cropping systems. The ‘milpa’ system associating maize, bean, squash, chilli and many other crops (Basurto et al., 1998), which was the main cropping system during the pre-Hispanic period, has been progressively substituted in most regions by continuous maize-cropping (Aguilar et al., 2003). Nitrogen application is generally low, because of high price ratios between fertilizer and grain, limited availability of fertilizer, low purchase power of farmers and risks of low efficiency due to excess or lack of rain (Aguilar et al., 2003). In some areas, poor farmers are practicing traditional, manual conservation tillage (Violicˇ, 1998). Soil is manually cleared and seeds are deposited in a hole made with a sharp wooden rod or coa. At harvest, maize straw is left on the soil. It is sometimes partially grazed by livestock. Information on the effect of zero tillage and residue conservation in continuous maize-cropping systems of Mexico is scarce. In the State of Jalisco (WestCentral Mexico), Scopel et al. (2001) showed that zero tillage and residue conservation allow a better capture and utilization of rainwater in the driest areas (400–500 mm per crop cycle). There are few studies on zero tillage and residue conservation in other regions of Mexico, particularly in the subtropical and tropical areas, and impacts other than grain yield variations have scarcely been analyzed (Erenstein, 1996). Mexico presents great variations in both altitude and latitude that are responsible for the great variety of climates, from extremely arid to tropical humid conditions, with large differences in annual mean rainfalls. Under these conditions zero tillage and residue conservation are expected to have vary-
97 ing impacts on soil and plant according to the region. Little is known about the potential effect of combining legume intercropping with zero tillage and residue conservation in the different regions. The aim of the present study was to describe and better understand the effects of zero tillage and residue management on yield and soil characteristics under a subtropical climate, according to climatic conditions and nitrogen availability. For this purpose, maize was cultivated during three years during the wet and dry seasons, under different treatments combining zero and conventional tillage, removing and conservation of residues, pure stand and intercropping with jackbean, Canavalia ensiformis L. (DC), and three nitrogen levels. Several soil and plant characteristics were assessed during the wet and dry seasons of the third year.
Materials and methods Experimental conditions The study was carried out during the wet season and the dry season of 2003–2004 at the Tlaltizapa´n experimental station of CIMMYT (Centro Internacional de Mejoramiento de Maiz y Trigo), located in the Mexican state of Morelos (Central Mexico). The station is 9908¢ W, 1841¢ N and elevation is 940 m above sea level.
The average depth of soil is 1.2 m, with bedrock underlying it. The soil is a black Vertisoil developed from calcareous subsoil (Isothermic Udic Pellustert USDA type). It is a heavy, cracking soil, showing marked shrinking and swelling with changes in moisture content. Clay, silt and sand content in the 0–30 cm soil layer are 41.2, 36.8 and 22.0%, respectively. Soil moisture at field capacity and permanent wilting point are 36 and 24% by weight, respectively. Soil pH is 7.6. At the beginning of the experiment in 2001, bulk density was 1.24, carbon concentration 1.9% and cation exchange capacity 40.3 meq 100 g)1. The climate is an A(w)0 type (hot subhumid with summer rainfall). Average annual rainfall is 840 mm, with an average annual temperature of 23 C (temperature range 1.5–39.5 C) (1969– 2005 period). Measurements of air temperature, precipitation, relative humidity (RH) and photosynthetically active radiation (PAR) during the experiment were taken with a weather station (Model Campbell Scientific, Inc. Model CR10X). Rainfall and temperature data for the wet and dry seasons are presented in Figure 1. Rainfall was 952 and 45 mm during the wet (June–October) and dry (December–April) seasons, respectively. In the wet season average daily values were 10.2 MJ m)2 day)1 for PAR and RH ranged from 40 to 95%. In contrast, in the dry season, PAR increased from 8.2 to 12.5 MJ m)2 day)1 through the cycle (data from the first and last weeks of the growth cycle, respectively) and max-
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Figure 1. Maximum and minimum daily temperatures, and rainfall distribution during the wet and dry seasons 2003–2004.
98 imum and minimum RH decreased until 58.2 and 14.9%, respectively.
Plant material and crop management A CIMMYT hybrid maize variety (CML78CML-321) was used in the study. The experiment was laid out in a split-plot design with tillage as main factor, split by residue management then split by nitrogen fertilization. The experimental design had two replicates of 18 treatments, corresponding to the combinations between two tillage treatments (To and Tc), three residue management treatments (Rm, Rmc and Ro) and three nitrogen treatments (N0, N100 and N200). Each plot consisted of 8 rows 5 m long with row spacing of 0.75 m. Distance between plants within the row was 0.25 m in all experiments. Under conventional tillage (Tc), 0.15–0.20 m deep mouldboard plough (tractor driven) was applied with disc harrowing before ridging. Seeds were manually sown and covered with a 2 cm soil layer. In zero tillage (To) treatment seeds were manually sown 3 cm deep using a stick. In all treatments, 2–3 seeds were sown in each hole, and plants were thinned at the V6 stage to obtain the desired plant population density (5.3 plants m)2, i.e., 168 plants per plot). In Rm treatment, maize residues were incorporated into the soil using a moldboard plough (in conventional tillage treatment) or left on the soil surface (in zero tillage treatment). In Rmc treatment, maize was associated with jackbean, Canavalia ensiformis L. (DC) and residues of both crops were incorporated to the soil (in conventional tillage treatment) or left on the soil surface (in zero tillage treatment). In the third treatment (Ro), residues were removed after harvest in both tillage treatments. In Rmc treatment jackbean was sown 35 days after maize, at a within row spacing of 0.5 m, in the maize furrow, according to De Herrera et al. (1993). Jackbean plants were cut just before soil preparation of the following season. Two levels of nitrogen fertilization N1 (100 kg ha)1) and N2 (200 kg ha)1) were manually incorporated approximately 5 cm under the soil surface near the plants, while in N0 treatment no nitrogen was applied. Ammonium sulfate (20.5% nitrogen) was used as the nitrogen fertilizer and applied on two dates (before sowing
and at the V6 stage). Before sowing 60 kg ha)1 of P2O5 (triple superphosphate with 46% P2O5) was applied to all plots. A pre-sowing irrigation was applied to all plots by sprinkler to prepare the soil. Then, water was applied by furrow irrigation approximately every two weeks. The last irrigation occurred during the week following female flowering. Seeds were treated before sowing with a mixture of an insecticide (thiodicarb) and fungicides (fludioxonil and metalaxyl). Weeds were controlled with a pre-emergent herbicide (2.24 kg ha)1+1.74 kg ha)1 s-metolachlor). Plants also had permethrin granules applied in the whorl to control fall armyworm (Spodoptera frugiperda).
Measurements At thinning, seedlings removed from each plot were counted and dried at 80 C to constant weight. Average dry weight of seedlings, thereafter referred as Bioms, provided an estimate of early growth in the different treatments. The number of days to reach 50% of plants with anther display (DA) and silking (DS) was recorded in all plots. Anthesis-silking interval (ASI) which has proved to be a good indicator of maize water stress (Edmeades et al., 1993) was calculated as DS ) DA. One day after DA 12 well-bordered plants were harvested in the six central rows of each plot, oven-dried at 80 C for three days to a constant weight and weighed to obtain the total above ground biomass dry weight at anthesis, thereafter referred as Bioma. After completion of male flowering, plant height (PH) was recorded on 10 plants per plot, as the distance between the ground surface and the node bearing the flag leaf. Variation in soil temperature was registered using a temperature sensor (Hobo S-TMAM0XX) connected to a Hobo Micro Station Data Logger (Hobo, Onset Computer Corporation, Bourne, MA). Temperature sensors were placed at a 5 cm depth in the plots T0-R0-N100 and T0-Rm-N100 at the beginning of the wet season to evaluate the effect of residues and in the plots TC-R0-N100 and T0-Rm-N100 at the beginning of the dry season to evaluate the effect of tillage. Root fresh mass at anthesis was estimated in dry season by root electrical capacitance
99 measurements, according to Chloupek (1972). Previous investigations indicated a significant correlation between root electrical capacitance and root fresh mass under field conditions (Van Beem et al., 1998). Root capacitance (RC) was measured using a BK Precision 810A hand-held capacitance meter (Maxtec International Corp., Chicago, IL), operating at a frequency of 1 kHz in the range between 200 pF and 2 lF (Van Beem et al., 1998). The negative electrode of the capacitance meter was connected to the maize stem via a battery clamp at 6 cm above ground level, while the positive electrode was connected to a copper ground rod inserted into the soil to a depth of 15 cm and positioned 5 cm away from the stem base. One capacitance measurement per plant was taken at 200 nF after allowing 5 s for the system to stabilize. Measurements were made just after an irrigation, early in the morning to prevent loss of moisture around the root system, on 10 plants per plot in the centre six rows. In vivo chlorophyll concentration of the ear leaf was assessed beginning 2 weeks after DA and continuing on a 2-week-interval, on 10 plants, using a portable chlorophyll meter (SPAD-502, Minolta, Tokyo, Japan) and was expressed in arbitrary absorbance (or SPAD) values (Dwyer et al., 1991). Since chlorophyll content in a leaf is closely correlated with leaf nitrogen concentration (Blackmer and Schepers, 1995), the measurement of chlorophyll provided an indirect assessment of leaf nitrogen status. At physiological maturity, the two border rows as well as the two plants at the two extremes of each row were eliminated. Jackbean plants (when present) were harvested in each plot and 12 maize plants were collected in the six central rows for biomass measurement. Maize and jackbean biomass was oven-dried at 80 C for three days to a constant weight and weighed to obtain the total above ground biomass dry weight at maturity (thereafter referred, in the case of maize, as Biomm). In Rm and Rmc treatments, maize and jackbean biomass were returned to their corresponding plots and laid in the furrow on the soil surface or incorporated, according to the tillage treatment. Grain yield (GY) and yield components were determined on the remaining plants (78 plants per plot). Biomass was then either removed, kept on the soil surface or incorporated, according to the treatment. Ears were counted and the
proportion of ears affected by ear rot (Stenocarpella ssp.) determined in each plot. Ears were shelled, grain was dried at 80 C to constant weight and grain weight was determined for each plot. Thousand kernel weight (TKW) was determined from 200 grain samples. Grains per ear (GPE) were calculated from grain yield, thousand kernel weight and ears per plant (EPP). Soil bulk density (db), nitrogen (N) and carbon (C) content, and soil microbial biomass organic carbon were assessed in the layer 0– 30 cm, in each plot, at the end of the experiment. Soil bulk density was evaluated by weighing undisturbed soil samples according to Blake and Hartge (1986). Soil nitrogen and carbon were determined by the flash combustion technique, using a NC2100 CNS Analyzer (CE Elantech Inc., Lakewood, NJ, USA). Soil microbial biomass organic carbon was determined using the fumigation-extraction method of Brookes et al. (1985). Biomass organic carbon was measured in 8 ml aliquots of the K2SO4 extracts by dichromate digestion and back titration with ferrous ammonium sulfate (Vance et al., 1987). Biomass C was calculated using the equation biomass C=2.64 EC, with EC=organic carbon from fumigated soil ) organic C from non-fumigated soil. Statistical analysis Season and treatment effects were evaluated on grain yield and yield components. Effects of treatments on yield components, biomass and physiological traits were also determined separately in each season. All effects were calculated using the Varcomp procedure of SAS version 8.1. (SAS Institute, 1987).
Results The effects of tillage and residue management techniques on grain yield and yield components highly differed according seasons. In the wet season, tillage treatment had a highly significant effect on GY, GPE, TKW, Bioms and Biomm and a significant effect on ears per plant EPP and Bioma (Table 1). Conversely, in the dry season, there was no effect of tillage on yield and yield components. Tillage significantly affected
100 Table 1. Effect of the different tillage, residue management and nitrogen treatments on maize grain yield, yield components and biomass in wet and dry seasons Source of variation
Table 2. Effect of the different tillage, residue management and nitrogen treatments on the anthesis-silking interval (ASI), leaf chlorophyll concentration (Chl), root capacitance (RC) and ear rot (ER) of maize
GY EPP GPE TKW Bioms Bioma Biomm PH
Wet season T (tillage) *** R (residue) NS N (nitrogen) *** TR NS TN NS RN NS TRN NS Dry season T (tillage) NS R (residue) NS N (nitrogen) *** TR NS TN NS RN NS TRN NS
Source of variation
* NS *** NS NS NS NS
*** * *** NS NS NS NS
** NS *** NS NS NS NS
*** *** NS NS NS NS NS
* NS NS NS NS NS NS
** NS *** NS NS NS NS
NS NS *** NS NS NS NS
NS NS *** NS NS NS NS
NS NS *** NS NS NS NS
NS NS *** NS NS NS NS
** NS * NS * NS NS
NS NS *** NS NS NS NS
NS NS *** * NS NS NS
NS NS *** *** * NS NS
***, **,* P
