Soybean maize strip intercropping:A solution for maintaining food security in China

The practice of intercropping leguminous and gramineous crops is used for promoting sustainable agriculture,optimizing resource utilization,enhancing biodiversity,and reducing reliance on petroleum products.However,promoting conventional intercropping strategies in modern agriculture can prove challenging.The innovative technology of soybean maize strip intercropping(SMSI)has been proposed as a solution.This system has produced remarkable results in improving domestic soybean and maize production for both food security and sustainable agriculture.In this article,we provide an overview of SMSI and explain how it differs from traditional intercropping.We also discuss the core principles that foster higher yields and the prospects for its future development.

Coordinated responses of leaf and nodule traits contribute to the accumulation of N in relay intercropped soybean

Maize(Zea mays L.)-soybean(Glycine max L.Merr.)relay intercropping provides a way to enhance land productivity.However,the late-planted soybean suffers from shading by the maize.After maize harvest,how the recovery growth influences the leaf and nodule traits remains unclear.A three-year field experiment was conducted to evaluate the effects of genotypes,i.e.,supernodulating(nts1007),Nandou 12(ND12),and Guixia 3(GX3),and crop configurations,i.e.,the interspecific row spacing of 45(I45),60(I60),75 cm(I75),and sole soybean(SS),on soybean recovery growth and N fixation.The results showed that intercropping reduced the soybean total leaf area(LA)by reducing both the leaf number(LN)and unit leaflet area(LUA),and it reduced the nodule dry weight(NW)by reducing both the nodule number(NN)and nodule diameter(ND)compared with the SS.The correlation and principal component analysis(PCA)indicated a co-variability of the leaf and nodule traits in response to the genotype and crop configuration interactions.During the recovery growth stages,the compensatory growth promoted soybean growth to reduce the gaps of leaf and nodule traits between intercropping and SS.The relative growth rates of ureide(RGR_U)and nitrogen(RGR_N)accumulation were higher in intercropping than in SS.Intercropping achieved more significant sucrose and starch contents compared with SS.ND12 and GX3 showed more robust compensatory growth than nts1007 in intercropping.Although the recovery growth of relay intercropping soybean improved biomass and nitrogen accumulation,ND12 gained a more significant partial land equivalent ratio(pLER)than GX3.The I60 treatment achieved more robust compensation effects on biomass and N accumulation than the other configurations.Meanwhile,I60 showed a higher nodule sucrose content and greater shoot ureide and N accumulation than SS.Finally,intercropping ND12 with maize using an interspecific row spacing of 60 cm was optimal for both yield advantage and N accumulation.

Insight into the effect of geographic location and intercropping on contamination characteristics and exposure risk of phthalate esters(PAEs)in tea plantation soils

Phthalate esters(PAEs)are an emerging pollutant due to widespread distribution in environmental mediums that have attracted widespread attention over recent years.However,there is little information about tea plantation soil PAEs.A total of 270 soil samples collected from 45 tea plantations in the major high-quality tea-producing regions of Jiangsu,Zhejiang,and Anhui provinces in China were analyzed for seven PAEs.The detection frequency of PAEs in tea plantation soil was 100%.DBP,DEHP,and DiBP were the main congeners in tea plantation soil.The PAEs concentrations in the upper soil were significantly higher than those in the lower soil.The concentration of tea plantation soil PAEs in Jiangsu Province was significantly lower than those in Zhejiang and Anhui provinces.Intercropping with chestnuts can effectively reduce the contamination level of PAEs in tea plantation soil.Correlation analysis,redundancy analysis,partial correlation analysis,and structural equation modeling methods further confirmed the strong direct influence of factors such as chestnut–tea intercropping,temperature,and agricultural chemicals on the variation of PAEs in tea plantation soil.The health and ecological risk assessments indicated that non-carcinogenic risk was within a safe range and that there was a high carcinogenic risk via the dietary pathway,with DBP posing the highest ecological risk.

Alternate cotton-peanut intercropping:a new approach to increasing productivity and minimizing environmental impact

Recent publications have highlighted the development of an alternate cotton-peanut intercropping as a novel strat-egy to enhance agricultural productivity.In this article,we provide an overview of the progress made in the alternate cotton-peanut intercropping,specifically focusing on its yield benefits,environmental impacts,and the underlying mechanisms.In addition,we advocate for future investigations into the selection or development of appropriate crop varieties and agricultural equipment,pest management options,and the mechanisms of root-canopy interactions.This review is intended to provide a valuable reference for understanding and adopting an alternate intercropping system for sustainable cotton production.

Assessing the Efficacy of Wheat-Soybean Based Intercropping System at Different Plant Densities in Bambili, Cameroon

Wheat is one of the most important cereals in the world, serving as a staple for millions globally. In the wake of the geopolitical crisis between Russia and Ukraine, it has become incumbent for many countries to invest in wheat production. Improving cropping systems for wheat production is paramount. Intercropping cereals with legumes has tremendous advantages. Therefore, this study was designed to optimize wheat production by intercropping it with soybean at different densities. Between March and August 2023, a randomized complete block design trial was conducted in Bambili, North West of Cameroon with treatments T1 (wheat monocrop at 200,000 plants ha−1), T2 (soybean monocrop at 250,000 plants ha−1), T3 (200,000 wheat and 125,000 soybean ha−1), T4 (100,000 wheat and 250,000 soybean ha−1), T5 (200,000 wheat and 250,000 soybean ha−1) and T6 (100,000 wheat and 125,000 soybean ha−1). Results revealed that growth parameters of wheat were not significantly influenced by monocrop or intercrop. The yield of wheat was significantly higher in the monocrop than the intercrop treatments, with slight variation amongst the intercrop treatments. Soybean yield was higher in the monocrop than in the intercrop, with no variations amongst the intercrop treatments. Only the land equivalence ratio (LER) for T5 was greater than 1.0. The competitive ratio for T5 was 0.54 for wheat and 1.90 for soybean, comparatively lower than the other monocrop treatments. Intercropping wheat and soybean at 200,000:250,000 ratio is recommended.

Sugarcane/soybean intercropping with reduced nitrogen addition enhances residue-derived labile soil organic carbon and microbial network complexity in the soil during straw decomposition

Sugarcane/soybean intercropping with reduced nitrogen addition is an important sustainable agricultural pattern that can alter soil ecological functions,thereby affecting straw decomposition in the soil.However,the mechanisms underlying changes in soil organic carbon(SOC)composition and microbial communities during straw decomposition under long-term intercropping with reduced nitrogen addition remain unclear.In this study,we conducted an in-situ microplot incubation experiment with^(13)C-labeled soybean straw residue addition in a two-factor(cropping pattern:sugarcane monoculture(MS)and sugarcane/soybean intercropping(SB);nitrogen addition levels:reduced nitrogen addition(N1)and conventional nitrogen addition(N2))long-term experimental field plot.The results showed that the SBN1 treatment significantly increased the residual particulate organic carbon(POC)and residual microbial biomass carbon(MBC)contents during straw decomposition,and the straw carbon in soil was mainly conserved as POC.Straw addition changed the structure and reduced the diversity of the soil microbial community,but microbial diversity gradually recovered with decomposition time.During straw decomposition,the intercropping pattern significantly increased the relative abundances of Firmicutes and Ascomycota.In addition,straw addition reduced microbial network complexity in the sugarcane/soybean intercropping pattern but increased it in the sugarcane monoculture pattern.Nevertheless,microbial network complexity remained higher in the SBN1 treatment than in the MSN1 treatment.In general,the SBN1 treatment significantly increased the diversity of microbial communities and the relative abundance of microorganisms associated with organic matter decomposition,and the changes in microbial communities were mainly driven by the residual labile SOC fractions.These findings suggest that more straw carbon can be sequestered in the soil under sugarcane/soybean intercropping with reduced nitrogen addition to maintain microbial diversity and contribute to the development of sustainable agriculture.

Several Cotton Rotation and Intercropping Systems in Cotton Planting Area of Eastern Henan Province

In recent years,the area dedicated to cotton cultivation in eastern Henan Province has experienced a continuous decline.Developing efficient multi-cropping systems for cotton and increasing the multiple cropping index represent effective strategies to stabilize the cotton planting area and enhance the income of cotton farmers.This paper presents an overview of intercropping systems and the benefits associated with cotton rotation and intercropping practices.Specifically,it discusses the"early maturing cotton-wheat"rotation system,the"cotton-watermelon"intercropping system,the"cotton-Dutch bean"intercropping system,and the"early maturing cotton-peanut-garlic"intercropping system.

Legume Green Manure and Intercropping for High Biomass Sorghum Production

Before the advent of cheap, synthetic fertilizers, legumes were commonly used as green manure crops for their ability to fix atmospheric nitrogen (N). A three-year study at Overton, TX examined legume integration into high-biomass sorghum (Sorghum bicolor L.) production systems on a Lilbert loamy fine sand recently cultivated after a fertilized bermudagrass [Cynodon dactylon (L.) Pers.] pasture. In this split-split plot design, ‘Dixie’ crimson clover (Trifolium incarnatum L.) and ‘Iron and Clay’ cowpea (Vigna unguiculata L.) were integrated into a high-biomass sorghum production system to evaluate impacts on N concentration, C concentration, and yield of high-biomass sorghum and their impacts on soil total N and soil organic carbon (SOC). Main plots were split into crimson clover green manure (CLGM) and winter fallow (FALL) followed by three sub-plots split into warm-season crop rotations: cowpea green manure (CPGM), cowpea-sorghum intercrop (CPSR), and sorghum monocrop (SORG). Three N fertilizer treatments (0, 45, 90 kg N∙ha−1) were randomized and applied as sub-sub plots. The CLGM increased (P sorghum biomass yield (16.5 t DM∙ha−1) 28% in year three but had no effect in the first two years. The CPSR treatment reduced sorghum yield up to 62% compared to SORG;whereas CPGM increased sorghum yield 56% and 18% the two years following cowpea incorporation. Rate of N fertilizer had no effect on sorghum biomass yield. Decrease in SOC and soil N over time indicated mineralization of organic N and may explain why no N fertilizer response was observed in sorghum biomass yield. Cowpea showed strong potential as a green manure crop but proved to be too competitive for successful intercropping in high-biomass sorghum production systems.

Assessment of Nitrogen Fixation, Uptake, and Leaching in Maize/Soybean Intercropping System at Varied Soil Depths and under Phosphorus Application in Chinese Agricultural Settings

The study of Nitrogen fixation, uptake, and leaching at different soil depths in the co-cultivation of maize and soybean under phosphorus fertilization is important for sustainable agriculture. This study was conducted in Quzhou, Hebei Province, China, with MC812 maize and Jidou12 soybean varieties. Soil samples were taken from each plot to create a composite sample. The results show that nitrogen concentration varies at different depths and is higher in all treatments between 40 and 100 cm. Incorporating intercropping of maize and soybeans into farming practices can lead to more sustainable and environmentally friendly agriculture in China.

Assessing the Influence of Phosphorus Fertilization on the Growth and Yield of Maize/Soybean Intercrop by Analyzing Nitrogen Uptake

Intercropping, particularly the combination of maize and soybeans, has been widely recognized for its potential to improve nitrogen uptake and promote sustainable agriculture. This study examines the patterns of nitrogen uptake in maize and soybean intercropping systems under different growth stages and phosphorus fertilization levels and investigates the influence of nitrogen uptake on growth parameters such as plant height, leaf area, and biomass accumulation in the maize/soybean intercrop under different phosphorus fertilization regimes. The study also collected chlorophyll samples at different growth stages of maize in monoculture and intercropping with maize or soybean. The results showed that plant height was greater in V10 in both fertilized and unfertilized treatments for intercropped maize and soybean, and chlorophyll concentration was higher in VT intercropped maize. The results also showed a higher accumulation of biomass. Understanding the growth dynamics of these plants in monoculture and intercropping systems and the impact of fertilization practices is crucial for optimizing crop productivity and sustainability in agricultural systems.

Influence of Fruit Tree Types and Arrangements on Yield, Quality and Economic Returns of Cotton of Intercropping System in Southern Xinjiang

[Objective] The aim was to provide a theoretical basis for stable and highly effective intercropping arrangements and scientific management measures by selecting apple, pear, peach, apricot, walnut, jujube and other fruit trees to study their influence on yield, fiber quality and economic returns of intercropped cotton in southern Xinjiang. [Method] Based on major cropping pattern in production, randomized block design was adopted to explore growth indicators, canopy micrometeorological indicators, yield and fiber quality in key growth stage. [Result] Shading has a significant effect on cotton canopy micro-environment and canopy diameter is proportional to shading effect. According to comparisons of the same tree type, the change of canopy micro-environment was as follows： under canopyouter canopymiddle points and peachpearapplewalnutjujube for comparisons among different tree types. Canopy diameter is directly proportional to the number of tree branch and boll weight reductions and shading is the main cause of yield reduction. The canopy expansion is the major cause of decline of light intensity, temperature and humidity of cotton canopy. [Conclusion] Fruit trees, which will promote cotton yield,quality and canopy-environment, are as follows： jujube walnut apple pear peach trees. In practice, trees, which are small in canopy or well trimmed, are popular in production, such as jujube trees, to improve cotton yield and fiber quality.

Effects of intercropping systems of trees with soybean on soil physicochemical properties in juvenile plantations

The intercropping system of tree with soybean in juvenile plantations, as a short-term practice, was applied at Lao Shan Experimental Station in Mao＇er Shan Forest of Northeast Forestry University, Harbin, China. The larch （Larix gmelinii）lsoybean （Glycine max.） and ash （Fraxinus mandshurica） intercropping systems were studied in the field to assess the effects of the intercropping on soil physicochemical properties. The results showed that soil physical properties were improved after soybean intercropping with larch and ash in one growing season. The soil bulk density in larch/soybean and ash/soybean systems was 1.112 g·cm^-3 and 1.058 g·cm^ 3, respectively, which was lower than that in the pure larch or ash plantation without intercropping. The total soil porosity also increased after intercropping. The organic matter amount in larch/soybean system was 1.77 times higher than that in the pure larch plantation, and it was 1.09 times higher in ash/soybean system than that in the pure ash plantation. Contents of total nitrogen and hydrolyzable nitrogen in larch/soybean system were 4.2% and 53.0% higher than those in the pure larch stand. Total nitrogen and hydrolyzable nitrogen contents in ash/soybean system were 75.5% and 3.3% higher than those in the pure ash plantation. Total phosphorus content decreased after intercropping, while change of available phosphorus showed an increasing trend. Total potassium and available potassium contents in the larch/soybean system were 0.6% and 17.5% higher than those in the pure larch stand. Total potassium and available potassium contents in the ash/soybean system were 56.4% and 21.8% higher than those in the oure ash plantation.

Impacts of soil fertility management on productivity and economics of rice and fodder intercropping systems under rainfed conditions in Odisha,India

Under small and marginal farm conditions,allocation of land exclusively for forages is not possible.Hence,integration of forages in existing crop geometry can ensure production of grain and fodder,simultaneously under rainfed conditions.Afield experiment was conducted to study the effect of different nutrient management practices on rice and fodder intercropping systems under rainfed conditions during 2015-2017.The intercropping system comprised(i)sole rice(R),(ii)rice and cowpea(5:2)(CP)and(iii)rice and ricebean(5:2)(RB)whereas the different nutrient management practices comprised(i)application of farm yard manure(FYM)at 5t ha^(-1)(farmers'practice)(N_(1)),(ii)application of inorganic fertilizer(recommended dose of fertilizer(RDF)of rice,60:30:30 kg ha^(-1) of N:P_(2)O_(5):K_(2)O)(N_(2))and(iii)application of both FYM at 5t ha^(-1) and 50%of RDF inorganic fertilizer(N3).The results of the experiment revealed that the growth attribute such as leaf area was influenced significantly when fodder crops were taken as intercrops because rice plant was getting more nitrogen from soil due to nitrogen fixation of leguminous fodder crops.Among the nutrient management practices,significant differences in leaf area were found beween N2 and and between N_(3)and N_(1)treatments.However,regarding total number of effective tillers,significant differences were found neither between nutrient management practices nor between cropping systems.The rice equivalent yield(REY)based on price(REY_(P))was found to be significantly lower in CP(2615 kg ha^(-1);-6.4%)and RB intercropping systems(2571 kg ha^(-1);-8.0%)than in R monocropping system(2794 kg ha^(-1)).However,the REY based on energy(REY_(E))of CP(2999 kg ha^(-1);+7.3%)and RB(2960 kg ha^(-1);+5.9%)were found to be significantly higher than that of R(2794 kg ha^(-1))irrespective of nutrient management practices.Between different nutrient management practices,the N3 treatment recorded the highest REY_(P)and REY_(E)which was at par with the N_(2)treatment and significantly higher than the N1 treatment irrespective of cropping systems.The combined application of both organic and inorganic sources of nutrients helped to supply nutrients throughout the growing season,which led to improved growth parameters and rice yield.The R monocropping system resulted in more income and rain water use efficiency(RWUE)closely followed by rice and fodder intercropping systems.However,the REYe and energy use efficiency(EUE)of rice and fodder intercropping systems were higher than those of R.Also,fodder helped to meet the requirement of cattle feeding in the off-season.Hence,the intercropping system is advocated in the study zone.Further study can be done on ecosystem services and carbon sequestration potential of the intercropping system,as well as the system's coping ability in response to short drought through observing periodic soil moisture regime in root zone.

Effect of Apple-tea Intercrop on the Growth and Yield of Tea Shoot

[Objective] The aim was to study the effect of apple-tea intercrop on the growth and yield of tea shoot.[Method] Comparing tea leaves in apple-tea intercrop garden with neighboring tea leaves,the change of tea growth and fresh leaves yield in annual growth cycle was observed.[Result] There was obvious difference of tea shoot growth in intercropping and control group in various seasons.In spring,summer and autumn,intercropping tea had lower canopy temperature and higher canopy humidity compared with control tea,while there was no obvious difference of canopy temperature and humidity in intercropping and control tea in winter;the respiratory intensity of intercropping tea was very significantly lower than that of control tea,and its net photosynthetic intensity was very significantly higher than that of control tea,while there was no obvious change law in photosynthetic rate;the effect of intercrop on budding density of tea shoot wasn＇t obvious,but it promoted early germination of tea bud,increased leaf weight and improved fresh leaf yield.[Conclusion] Our study could provide theoretical foundation for the rational allocation of intercrop in compound ecological tea garden and the production of non-polluted tea.

Effect of Intercropping and Nitrogen Regulation on Nitrate and Apparent Loss of Nitrogen in Soil

[Objective] The aim was to investigate effect of intercropping and nitrogen regulation on nitrate and apparent loss of nitrogen, providing theoretical references for reasonable fertilization and pollution reduction. [Method] In the research, deeprooted eggplants and shallow-rooted scallions were intercropped with nitrogen regulat- ed to study on effect of the cropping system on temporal and spatial changes of ni- trate nitrogen and apparent loss of nitrogen. [Result] When the fertilizers were re- duced, contents of nitrate were less in intercropped field than that in mono-cropped one, indicating that eluviation of nitrate would be blocked and nitrate accumulation would be lowered effectively by intercropped eggplants and scallions. With intercrop- ping adopted, the reduced fertilizers would lower nitrate content in soil, deep soil in particular, and nitrate was significantly lower than that fertilized with conventional quantity during vegetable growth period. In addition, nitrate accumulation in soil profiles was also significantly shorter in field applied with reduced fertilizers than that with conventional one. It was shown that intercropping and fertilizer reduction would both cut apparent loss of nitrate down in varying degrees. [Conclusion] The research lays basis for high production of vegetables, reasonable fertilization and pollution reduction.

Highly-efficient Intercropping Mode and Selection of Suitable Peanut Varieties in Maize and Peanut Intercropping Systems

[Objective] The aim was to explore efficient maize and peanut intercrop-ping mode and select suitable peanut varieties of the mode in Yungui Plateau. [Method] In the test, 6 cropping methods were set by randomized block design. Yields and economic benefits were measured in mature stage with Excelland DPS. [Result] Compared with monoculture, maize and peanut intercropping systems took advantages and LER values were proved higher than 1. In the intercropping system with maize and Yun peanut No.3 at 2∶2, in particular, the value of LER was 1.40 and compound yield reached 9 036 kg/hm2; the net output values of maize kernel and fresh/dry peanut pod increased by 182.63% and 140.59%, compared with maize by monoculture. In addition, the output values of Yun peanut No.3 by monoculture and intercropping system increased by 5 069 and 3 272 yuan/hm2, respectively, than Yanshan conventional peanut varieties. [Conclusion] The efficient intercropping system with maize and peanut mode at 2∶2 mode in Yungui plateau and the Yun peanut No.3 exhibited higher yield and economic benefit advantages, compared with Yanshan conventional planting peanut varieties.

Effects of Different Intercropping Modes on Growth, Yields and Economic Benefit of Cassava and Peanut in Symbiotic Period

[Objective] This study was conducted to investigate effects of different intercropping modes on growth, yields and economic benefit of cassava and peanut in symbiotic period. [Method] With sole cropping of cassava （M1） and sole cropping of peanut （M2） as control groups, effects of intercropping of cassava with 1 row, 2 rows and 3 rows of peanut （M3, M4 and M5）on crop growth, yields and economic benefit were studied. [Result] Intercropping affected both growth and yields of cassava and peanut. Growth competition existed between cassava and peanut, and plant heights of cassava and peanut changed similarly. In late stages of intercropping, treatments M1, M2 and M5 showed higher plant heights under no nitrogen application, while treatment M3 and M4 exhibited higher plant heights under nitrogen application; intercropping improved leaf temperature, but no obvious law could be observed among different intercropping treatments; and intercropping improved total dry matter amount, which was the highest in M5 in root expanding stage and on the 30th day of the expanding stage, and the highest in M4 on the 60th day of the expanding stage. Intercropping reduced the yield of single plant, but improved the economic benefit of red upland soil; and under no nitrogen application and nitrogen application, cassava yields decreased by 25.35% and 14.55%, respectively, peanut yields decreased by 28.76% and 52.60%, respectively, while economic benefit increased by 72.90% and 56.82%, respectively. [Conclusion] Compared with sole cropping, interplanting cassava with 1 row, 2 rows or 3 rows of peanut could all improve economic benefit, and the economic benefit increased with number of rows of interplanted peanut increasing.

Research on Efficiency Improving Technology for Intercropping Sesame (Sesamum indicum) and Peanut (Arachis hypogaea)

[Objective] The research aimed to establish a optimized combination of intercropping and fertilization application technology of intercropping sesame （Sesamum indicum） and peanut（Arachis hypogaea）. [Method] Double factor randomized block design （2 fertilization methods and 5 ratios） was adopted, with 10 treatments, 3 repeats. There were a total of 30 plots, with plot area of 12.0 m2. Two fertilization methods included C1 [base fertilizer （540 g/plot compound fertilizer ＋ topdressing （90 g urea）] and C2 [all as base fertilizer （540 g/plot compound fertilizer）]. Five different proportions （sesame： peanut） were M1（2∶4）, M2（2∶6）, M3（1∶4）, monoculture sesame （CK1） and monoculture peanut （CK2）, respectively. [Result] Output value and land equivalent ratio （LER） of C1M2 treatment （6 lines peanut/2 lines sesame, base fertilizer 540 g/plot （compound fertilizer） ＋ （topdressing urea 90 g） were the highest of 22 378.68 yuan/hm2 and 1.56 respectively; sesame yield was 641.64 kg/hm2 and peanut yield was 2 506.67 kg/hm2. Output-input ratio was 4.94. The income was increased by 32.32% and 95.97% compared with only planting of peanuts and sesame. [Conclusion] The study provided a theoretical basis for finding the best intercropping combinations of sesame and peanut and rational application fertilizations.

Greenhouse Intercropping of Green Asparagus(Asparagus officinalis Linn) and Coriander(Coriandrum sativum L.)

Greenhouse cultivation in northern China has the characteristic of single mode, and the intercropping mode is not common. Greenhouse intercropping of green asparagus （Asparagus officinalis Linn） and coriander （Coriandrum sativurn L.） not only could increase vegetable kinds, but also could improve cropping index, and the asparagus growers＇ income could also be improved. This paper introduced the intercropping technique of green asparagus and coriander, so as to provide technical support for large-area extension of greenhouse green asparagus cultivation and break the situation of single mode for .qreenhouse cultivation.

Analysis on Waxy Corn/Soybean Intercropping Pattern and Economic Benefit

The research mainly analyzed effects of waxy corn/soybean intercropping on yields of the two crops, as well as agronomic characters, and the economic benefits of the mode. The results showed that although yields of waxy corn and soybean went down by 21.19% and 31.04% per unit area, land equivalent ratio（1.48） kept higher than 1, suggesting the intercropping improves land use rate. Besides, due to the practice of intercropping, many characters of waxy corn grew, but of soybean declined. The economic benefits from high to low were waxy corn/soybean intercropping, monoculture of waxy corn, and monoculture of soybean.