Non-crop Period Research Articles

Fine Resolution Mapping of Soil Organic Carbon in Croplands with Feature Selection and Machine Learning in Northeast Plain China

Unsustainable human management has negative effects on cropland soil organic carbon (SOC), causing a decrease in soil health and the emission of greenhouse gas. Due to contiguous fields, large-scale mechanized operations are widely used in the Northeast China Plain, which greatly improves production efficiency while decreasing the soil quality, especially for SOC. Therefore, an up-to-date SOC map is needed to estimate soil health after long-term cultivation to inform better land management. Using Quantile Regression Forest, a total of 396 soil samples from 132 sampling sites at three soil depth intervals and 40 environmental covariates (e.g., Landsat 8 spectral indices, and WorldClim 2 and MODIS products) selected by the Boruta feature selection algorithm were used to map the spatial distribution of SOC in the cropland of the Northeast Plain at a 90 m spatial resolution. The results showed that SOC increased overall from the southern area to the northern area, with an average of 17.34 g kg−1 in the plough layer (PL) and 13.92 g kg−1 in the compacted layer (CL). At the vertical scale, SOC decreased, with depths getting deeper. The average decrease in SOC from PL to CL was 3.41 g kg−1. Climate (i.e., average temperature, daytime and nighttime land surface temperature, and mean temperature of driest quarter) was the dominant controlling factor, followed by position (i.e., oblique geographic coordinate at 105°), and organism (i.e., the average and variance of net primary productivity in the non-crop period). The average uncertainty was 1.04 in the PL and 1.07 in the CL. The high uncertainty appeared in the area with relatively scattered fields, high altitudes, and complex landforms. This study updated the 90 m resolution cropland SOC maps at spatial and vertical scales, which clarifies the influence of mechanized operations and provides a reference for soil conservation policy-making.

Occurrence and diversity of arbuscular mycorrhizal fungi colonising off-season and in-season weeds and their relationship with maize yield under conservation agriculture

Weeds are responsible for major crop losses worldwide but can provide beneficial agroecosystem services. This study aimed to elucidate how arbuscular mycorrhizal fungi (AMF) in weeds respond to host identity and conservation agricultural practices. The study was carried out at two locations in Southern Africa during off-season and in-season maize cultivation. Off-season AMF root colonisation, diversity indices and community composition significantly differed among weed species at both locations. Glomus sp. VTX00280 explains most of the AMF community differences. In-season, implementation of conventional tillage with mulching alone (CT + M) or together with crop rotation (CT + M + R) resulted in a 20% increase in AMF colonisation of the constantly occurring weed species, Bidens pilosa (BIDPI) and Richardia scabra (RCHSC), compared with conventional tillage plus rotations (CT + R). The diversity of AMF was highest under no-tillage plus mulching (NT + M). Off-season and in-season AMF structures of both BIDPI and RCHSC were not related, but 39% of the taxa were shared. Structural equation modelling showed a significant effect of the cropping system on weed AMF diversity parameters and weed and maize root colonisation, but no significant influence of weed root AMF traits and maize colonisation was detected on maize yield. This may be explained by the improvement in weed competitive ability, which may have offset the AMF-mediated benefits on yield. Our findings highlight that implementing M and CR to CT and NT positively affected weed AMF colonisation and diversity. The similarity between the off-season and in-season AMF composition of weeds supports the fact that weeds functionally host AMF during the non-crop period.

Conservation agriculture practices have changed habitat use by rodent pests: implications for management of feral house mice

The advent of ‘conservation agriculture’ (CA) farming using zero- or no-tillage practices and an accompanying change in crop rotations in the last 10–15 years has potentially led to less disturbance of mouse burrows and increased cover and food supply. Given the irregular outbreaks of mice in grain cropping regions in Australia and the damage they cause, it is important to understand when and where mouse populations increase so that management strategies can be improved. We utilised a 20-year long-term mouse population data set collected prior to the introduction of CA farming practices and a more recent 8-year data set after CA to compare changes in mouse population abundance in a typical dryland grain cropping system in north-western Victoria, Australia. Mouse trapping data were used to compare abundance in crop and margin habitats during crop growth and non-crop (fallow) periods before (‘conventional’) and after introduction of CA. Mice are now resident year-round within crops and stubble and appear to only spill over into margin habitats. Previously developed recommendations for mouse management that include their control while in margin habitats may no longer be valid.

Impact of water table levels and winter cover crops on greenhouse gas emissions from cultivated peat soils

Drainage and cultivation have turned peatlands from carbon (C) sinks into hotspots for greenhouse gas (GHG) emissions. Raising the water table and planting of winter cover crops are potential strategies to help reduce peat oxidation and re-initiate net C accumulation during the non-cropping period. However, the effects of these practices as well as their interactions on GHG emissions remain unclear. Here, we carried out an outdoor mesocosm experiment to elucidate the effect of water table levels (−30 cm and −50 cm) and winter cover crop cultivation (vetch, rye, no plant) on carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) fluxes during the winter period (November-April). Soil-atmosphere GHG exchange, GHG concentrations within the peat profile and soil water solute concentrations were monitored. Our results showed that high water table significantly reduced ecosystem respiration, while it had no net effect on N2O and CH4 fluxes. Uptake of available N by the cover crop significantly reduced nitrate in soil solution, thereby lowering the potential for leaching and both direct and indirect N2O emissions. No interactive effects between water table levels and cover crops were detected for any of the measured GHG fluxes. Seasonal variations of GHG fluxes were positively correlated with soil air concentrations at −15 cm and −40 cm depths, which were further regulated by dissolved organic C, nitrate concentration, and anaerobic conditions in the soil. This study suggests that there is great potential to raise water table levels and introduce green cover crops to reduce GHG emissions. Further studies are needed to achieve a complete evaluation of these strategies outside of the growing season, which may provide a significant mitigation benefit in C-rich cultivated peatlands.

Non-cropping period accounting for over a half of annual nitric oxide releases from cultivated calcareous-soil alpine ecosystems with marginally low emission factors

Nitric oxide (NO) emissions from alpine ecosystems conventionally being long-term cultivated with feed crops are not well quantified. The authors attempted to address this knowledge gap by performi...

Probabilities of having minimum amounts of available soil water at wheat planting

Winter wheat (Triticum aestivum L.)-fallow (WF) remains a prominent cropping system throughout the Central Great Plains despite documentation confirming the inefficiency of precipitation storage during the summer fallow period. Wheat yield is greatly influenced by available soil water at planting, and that quantity is influenced by cropping intensity, tillage intensity, crop grown prior to winter wheat planting, and length of the non-crop period prior to winter wheat planting. The objective of this study was to determine the effect of cropping system intensity, tillage, and crop prior to wheat planting on available soil water at planting and the probabilities of having certain minimum amounts of available soil water at wheat planting. Available soil water was measured at wheat planting for nine cropping systems varying in fallow frequency, tillage intensity, and crop prior to wheat over a 25-yr period at Akron, CO. Available soil water at wheat planting was found to be greatest (average 218 mm) for no-tillage (NT) and reduced-tillage (RT) systems in which a fallow period of 12–14 months preceded wheat planting. The lowest amounts of available soil water at wheat planting were found for the continuously cropped rotations (average 100 mm). The cumulative probability exceedance graphs of available soil water at planting fell into three groupings: 1) the five rotations that had a NT or RT fallow period prior to the next wheat crop; 2) the WF (conventional till) rotation; 3) the three rotations with either pea (Pisum sativum L.) or proso millet (Panicum miliaceum L.) prior to the next wheat crop. These graphs provide a valuable decision support tool for helping farmers assess risk in moving from a WF cropping system to a system of greater cropping intensity and diversity.

Water use and environmental parameters influence proso millet yield

Proso millet (Panicum miliaceum L.) is a short-season, drought-tolerant C4 species capable of making use of limited available water supplies and is suitable for dryland crop rotations in the Central Great Plains. Previously published water use/yield production functions for proso millet have slopes lower than reported for other C4 species in this region. The objectives of this experiment were to determine the water-limited yield relationship for proso millet and to identify environmental factors that cause yields to be lower than predicted by the water-limited yield relationship. Water use and yield data were obtained from a long-term crop rotation experiment conducted under dryland conditions in northeast Colorado from 1995 to 2016. Stepwise linear regression analysis was used to determine important environmental factors influencing yield. The water-limited yield relationship had a slope consistent with other C4 species in this region (32.57kgha−1 per mm of water use). A relationship based on growing season water use, plant available soil water at planting, precipitation received from 12 to 18 August, number days in July and August with maximum temperature greater than 36°C, daily average wind run and maximum wind gust during the week before swathing explained 88% of yield variability. The results of this analysis suggest that closing the yield gap for proso millet production could likely result from efforts to breed for enhanced shattering resistance and heat tolerance and from production methods that improve precipitation storage efficiency during the non-crop period prior to millet planting and increase available soil water at millet planting.

Solute dynamics and the Ontario nitrogen index: I. Chloride leaching

The nitrogen (N) index for humid temperate southern Ontario, Canada (Ontario N index) incorporates previous and current crop type, fertilizer and (or) manure management, and hydrologic soil group (HSG) to estimate risk for contamination of tile drainage water and groundwater by nitrate leached below the primary crop root zone (top 60 cm of soil). The Ontario N index has received limited ground-truthing, and the leaching component was assessed using chloride tracer (ClTR) on five soils (one sandy loam, two loams, and two clay loams) representing four HSG-based risk levels (HSG-A, high risk; HSG-B, medium risk; HSG-C, low risk; HSG-D, very low risk). A square-wave pulse of ClTR was applied to the soil surfaces in fall 2007 as KCl, and movement and loss of ClTR was tracked over 1–1.2 years using monthly soil core samples collected from the top 60–80 cm. For all five soils, 60–96% of ClTR was leached out of the primary crop root zone (below 60 cm depth) during the noncropping period (October 2007 to March 2008 inclusive), and >80% was leached out of the root zone within 1 year. The percentage of ClTR that leached did not correlate with precipitation or HSG designation, but produced significant (P < 0.05) power function regressions with minimum and harmonic mean saturated soil hydraulic conductivity (Ksat) measured in the top 50–60 cm. ClTR leaching rate appeared to be controlled primarily by Ksat in a manner consistent with infiltration and solute transport theory. It was consequently proposed that solute leaching loss versus Ksat relationships may improve N index risk estimates for both southern Ontario and other humid temperate regions.

Greenhouse gases emission from paddy soil during the fallow season with and without winter flooding in central Japan

Many papers on measurements of greenhouse gases (GHGs) emission in rice paddies during a rice cropping season have been published. During a non-cropping season between Nov. and Apr., we investigated direct and indirect GHGs emissions in rice paddies. The indirect GHGs emission was evaluated as the amount of dissolved gases leaching from the paddy fields. Water management practices for the experiment were (1) continuous flooding (CF) and (2) non-flooding (NF). Although the direct CO2 emission in the CF treatment was remained nearly zero during the non-cropping period, direct CO2 emission in the NF treatment was continuously observed throughout the non-cropping period. The concentration of dissolved N2O in the NF treatment was below the detection limit of the instrument during the non-cropping period except immediately after the flooding and before the drainage. The concentration of dissolved N2O kept approximately 2 µg L−1 during the non-cropping period in the CF treatment. The direct CH4 emission and dissolved CH4 were not observed during the non-cropping period. Total gas emission in the NF treatment was 10 times as large as that in the CF treatment. Direct CO2 emission accounted for more than 90 % of the total emission in both treatments.

Cumulative deficit irrigation effects on corn biomass and grain yield under two tillage systems

Deficit irrigation (DI) is sometimes used to cope with dwindling irrigation water supplies or limited water allocations. A study at Akron, Colorado, USA from 2001 to 2006 investigated the effects of consecutive years of DI on soil water use, soil water content, biomass production, grain yield and water use efficiency (WUE) in a continuous corn system. In 2001, DI and full irrigation (FI) had the same grain yield. In 2002, DI reduced grain yield by 20% relative to FI. By 2006, continued DI reduced grain yield by 65% compared with FI. Significant increases in soil water storage during the non-crop period occurred only in 2005 and 2006. This resulted in a slow but continual decrease in soil water storage as the years progressed. By 2006, soil water storage in the 60- to 90-cm depth remained lower for DI than for FI during the entire growing season. WUE declined for DI compared with FI over the years. WUE was the same for DI and FI in 2001, but WUE for DI declined to only 65% of FI by 2006. DI may be an option for short term or emergency situations when insufficient irrigation water is available for FI in one year. However, long-term use of DI, without replenishment of stored soil water during the non-cropped period, was detrimental to both corn production and water use efficiency under these experimental conditions.

Reducing nitrogen loss with managed drainage and polymer-coated urea.

Continuous corn ( L.) production during dry years combined with high N fertilizer rates can have a high potential for NO-N loss through tile drainage water. Claypan soils can further increase the potential for NO-N loss through tile drainage water due to the claypan layer that restricts N leaching below the tile drains. The objective of this 4-yr study was to determine whether use of managed subsurface drainage (MD) in combination with a controlled-release N fertilizer could reduce the annual amount of NO-N loss through tile drainage water compared with free subsurface tile drainage (FD) with a noncoated urea application. Due to dry conditions over the summer and fall months, MD reduced the annual amount of water drained by at least 73% compared with FD in two of the four crop years. Low N loss and reduced corn N uptake possibly resulted in carry-over N and high soil N concentrations throughout the study, which may have limited the effect of N fertilizer source on annual NO-N loss in the tile drainage water. Use of MD reduced annual NO-N loss in the tile drainage water by 78 to 85% in two of the four years. High NO-N loss reduction with MD compared with FD was largely due to dry growing season conditions in combination with wet conditions over the noncropping period.

Rhizosphere microbial communities associated with Rhizoctonia damage at the field and disease patch scale

Rhizoctonia solani AG-8 is a major root pathogen in wheat (Triticum aestivum L.) systems worldwide and while natural disease suppression can develop under continuous cropping, this is not always the case. The main aim of our work was to elucidate the rhizosphere microbial community underlying a Rhizoctonia suppressive soil (Avon, South Australia) and to investigate how this community may develop in agricultural soils conducive to disease and of different soil type (Galong and Harden, New South Wales). The Avon suppressive soil community included Asaia spp. and Paenibacillus borealis, which were absent from a paired non-suppressive site. At Galong, soil taken from inside and outside disease patches showed no evidence of suppression, and disease suppression could not be transferred from the suppressive soil to the conducive soil from a different soil type and climatic area. 16S rRNA microarray analysis revealed Pseudomonas spp. were significantly more abundant inside than outside three disease patches at Galong. However, a survey of 32 patches across a range of stubble and tillage treatments at a nearby site showed no correlation between Pseudomonas and disease incidence. R. solani levels were significantly lower when stubble was retained rather than burnt or when nutrients (N, P and S) were incorporated with stubble during the non-crop period. Our results suggest soil type is an important factor for suppressive capability and that where specific disease suppression is absent, agronomic practice to increase soil carbon can encourage a non-specific microbial response that limits disease severity.

Reducing Nitrogen Loss in Subsurface Tile Drainage Water with Managed Drainage and Polymer-Coated Urea in a River Bottom Soil

Poorly-drained, river bottom soils can be high corn (Zea mays L.) yielding environments, but saturated soil conditions often reduce corn yields. Wabash soils located in river bottoms in Northeast Missouri have not been traditionally tile drained due to high clay content which requires narrow tile drain spacings. Increased land prices in the region have increased interest in tile draining poorly-drained bottom land soils to increase corn yields which could have a deleterious effect on water quality. The objectives of the three-year study were to determine whether use of managed subsurface drainage (MD) in combination with a controlled release N fertilizer could reduce the annual amount of NO3--N loss through tile drainage water compared to free subsurface drainage (FD) with a non-coated urea application. Annual NO3--N loss through tile drainage water with FD ranged from 28.3 to 90.1 kg·N·ha-1. Nitrogen fertilizer source did not affect NO3--N loss through tile drainage water, which was likely due to limited corn uptake over the three-year study due to adverse weather conditions. Averaged over three years, MD reduced tile water drained 52% and NO3--N loss 29% compared to FD. Reduction in NO3--N loss through tile drainage water with MD compared to FD was due to reduced tile flow during the non-cropping period. Annual flow-weighted mean concentration of NO3--N in the tile water was 5.8 mg·N·L-1 with FD and 8.1 mg·N·L-1 with MD. Tile draining river bottom soils at this location for continuous corn production may not pose a health risk over the evaluated duration.

Nitrogen Source and Placement Effects on Soil Nitrous Oxide Emissions from No‐Till Corn

A nitrogen (N) source comparison study was conducted to further evaluate the effects of inorganic N source and placement on growing-season and non-crop period soil nitrous oxide (NO). Commercially available controlled-release N fertilizers were evaluated for their potential to reduce NO emissions from a clay loam soil compared with conventionally used granular urea and urea-ammonium nitrate (UAN) fertilizers in an irrigated no-till (NT) corn ( L.) production system. Controlled-release N fertilizers evaluated were: a polymer-coated urea (ESN), stabilized urea (SuperU), and UAN+AgrotainPlus (SuperU and AgrotainPlus contain nitrification and urease inhibitors). Each N source was surface band applied (202 kg N ha) near the corn row at emergence and watered into the soil the next day. Subsurface banded ESN (ESNssb) and check (no N applied) treatments were included. Nitrous oxide fluxes were measured during two growing seasons and after harvest using static, vented chambers. All N sources had significantly lower growing-season NO emissions than granular urea (0.7% of applied N), with UAN+AgrotainPlus (0.2% of applied N) and ESN (0.3% of applied N) having lower emissions than UAN (0.4% of applied N). Similar trends were observed when expressing NO emissions on a grain yield and N uptake basis. Corn grain yields were not different among N sources but were greater than the check. Selection of N fertilizer source can be a mitigation practice for reducing NO emissions in NT, irrigated corn in semiarid areas. In our study, UAN+AgrotainPlus consistently had the lowest level of NO emissions with no yield loss.

CHANGES IN LAND COVER AND USE AFFECT THE LOCAL AND REGIONAL CLIMATE IN PIRACICABA, BRAZIL (doi: 10.4090/juee.2008.v2n2.068074)

Land use and changes in land cover play an important role in local and regional climatic conditions, especially in tropical regions. Piracicaba, a city in southeastern Brazil, has an economy that is based primarily on sugar cane cultivation. The seasonality of this crop means that there are marked annual fluctuations in land use and cover in this municipality. In this work, we investigated the seasonal variation in urban heat-islands and local climatic variations by using remote sensing data, geographic information system (GIS) and atmospheric modeling. The urban heat-islands were analyzed by using Landsat 7 (Enhanced Thematic Mapper+) images for the sugar cane crop (January to March) and non-crop (August to November) periods, and these images were subsequently converted to land surface brightness temperature. The average temperature in the non-crop period was 3.5°C higher than in the crop period, which suggested that heat-island intensity may be linked to the seasonality of sugar cane cultivation. In order to examine the influence of urban areas on regional temperature changes and heat fluxes, numerical simulations were done with the Brazilian Regional Atmospheric Modeling System (BRAMS). Overall, the results obtained suggested that local and regional climatic dynamics were related to land use and changes in land cover.

Changes in land cover and use affect the local and regional climate in Piracicaba, Brazil

Land use and changes in land cover play an important role in local and regional climatic conditions, especially in tropical regions. Piracicaba, a city in southeastern Brazil, has an economy that is based primarily on sugar cane cultivation. The seasonality of this crop means that there are marked annual fluctuations in land use and cover in this municipality. In this work, we investigated the seasonal variation in urban heat-islands and local climatic variations by using remote sensing data, geographic information system (GIS) and atmospheric modeling. The urban heat-islands were analyzed by using Landsat 7 (Enhanced Thematic Mapper+) images for the sugar cane crop (January to March) and non-crop (August to November) periods, and these images were subsequently converted to land surface brightness temperature. The average temperature in the non-crop period was 3.5°C higher than in the crop period, which suggested that heat-island intensity may be linked to the seasonality of sugar cane cultivation. In order to examine the influence of urban areas on regional temperature changes and heat fluxes, numerical simulations were done with the Brazilian Regional Atmospheric Modeling System (BRAMS). Overall, the results obtained suggested that local and regional climatic dynamics were related to land use and changes in land cover.

Evaluation of Loading Rate of Nitrogen from Rice-Paddies by Small Watershed Method

Nitrogen concentrations of drainage, percolation and irrigation were monitored periodically once a week at the experimental small rice-paddy watershed (EPW, 6.96 ha) for three years. Water level of the draining ditch was recorded continuously at the end of EPW. During the cropping period, load L of nitrogen through the drainage were evaluated from the concentrations C and the flow rates Q by integration interval method. During the non-cropping period, L was calculated from L(Q)-equations and Q. The L(Q)-equations were derived from the data measured during storm-runoff events. Concentrations of total nitrogen (TN) of irrigation, drainage and percolation were 0.403, 1.39 and 1.11 mg l-1, respectively, on average for three years. L of the drainage changed in wide range in response to agricultural practices and rainfalls; e.g. puddling, transplanting, fertilizing and plowing. The annual net-load of TN (unit load Ln) was 35.8±4.05 kg ha-1 y-1 on average for three years, of which the non-cropping period occupied 37 %. L for the puddling and transplanting period was discharged 27% of Ln, and strongly affected by the applied volume of irrigation. These results suggest that observations for only cropping periods or for only one year are insufficient for evaluating the precise Ln to assess the effect of the nitrogen discharged from paddy fields on lakes.

Potential for Soybean Cyst Nematode Reproduction on Winter Weeds and Cover Crops in Tennessee

The soybean cyst nematode (SCN), Heterodera glycines, is a major yield limiting pest of soybean (Glycine max). Current SCN management strategies include resistant soybean varieties and rotation with non-host crops. Increased adoption of the early soybean production system (ESPS) combined with a greater incidence of winter weeds from no-tillage practices may increase the population density of SCN during the noncrop period since several winter weeds and cover crops are hosts for SCN. A field experiment with a split-strip design was conducted over three years to evaluate whether SCN reproduced on weeds and cover crops during the noncrop period. Winter weeds and crimson clover roots were examined for females and cysts with eggs. The soil was sampled to determine if an increase in SCN egg population density occurred. We found no indication of SCN reproduction on winter weeds during the noncrop period or on the cover crop crimson clover. Accepted for publication 2 November 2006. Published 26 February 2007.

MANAGEMENT FACTORS CONTRIBUTING TO NITRATE LEACHING LOSS FROM A GREENHOUSE-BASED INTENSIVE VEGETABLE PRODUCTION SYSTEM

Considerable nitrate (NO3 - ) contamination of underlying aquifers is associated with greenhouse vegetable production in Almeria, Spain. Eighty percent of cropping occurs in soil, the rest in “open” hydroponic systems. To identify the management factors associated with NO3 - leaching loss from soil-based cropping, a survey of irrigation and N management practices was conducted on commercial farms, and a field study was conducted using lysimeters. The survey of management practices showed that N and irrigation management were based mostly on experience. Approximately one third of greenhouses were clearly applying total irrigation volumes during the growing season that were in excess of crop water requirements. In the first six weeks after transplanting, excessive volumes were applied in most greenhouses. All farmers routinely used large irrigations during the non-cropping period to apply soil disinfectant, to wet the soil profile before transplanting a new crop, and to leach salts. N supplied by sources other than mineral N fertiliser such as manure or soil mineral N was seldom considered when developing N fertiliser plans. Very large applications of manure had been applied in most greenhouses. In the field study, appreciable NO3 - leaching occurred following large irrigations given for soil management purposes and in the first three weeks of the crops as a result of large pre-transplant irrigations and frequent irrigation just after transplanting. NO3 - concentration in drainage was generally 6–12 mmol L -1 (350–600 mg NO3 - L -1 ), even when nutrients were not applied. Overall, these studies suggest that mineralisation of soil organic N, from manure applications, and/or accumulation of soil mineral N during cropping created a risk for NO3 - leaching, and that drainage associated with irrigations during the non-cropping period and in the early phase of the crop resulted in appreciable NO3 - leaching loss.

Crop Sequencing to Improve Use of Precipitation and Synergize Crop Growth

Cropping systems will not be sustainable without change. Broad‐scope problems associated with developing sustainable cropping systems are how to choose and sequence crops in cropping systems. Our objectives were twofold: (i) evaluate impacts of crop sequencing on precipitation use and (ii) show how crop sequencing can accentuate synergistic interactions among crops. Crop–fallow systems that developed in the Great Plains resulted in precipitation storage efficiencies of about 20% in the early 1930s to about 40% in the late 1980s. Integrated crop–livestock systems have been developed in the southern Great Plains to take advantage of bimodal annual precipitation pattern to produce high quality pigeonpea [Cajanus cajan (L.) Millsp.] forage during the noncrop period between winter wheat (Triticum aestivum L.) harvest and seeding. Pigeonpea can be grown after a mid‐June winter wheat harvest since pigeonpea uses precipitation received from wheat harvest to late September and pigeonpea has a root system that allows it to use soil water below the effective rooting depth of wheat. In the central Great Plains, water‐use efficiency of winter wheat was improved 18 to 56% by including broadleaf crop in a grass‐based rotation. Cropping systems in the northern Great Plains tend to be more diverse, and research at Mandan, ND, suggests that seed yield of flax (Linum usitatissium L.) can be tripled with a safflower (Carthamus tinctorius L.)–flax crop sequence vs. a flax–flax crop sequence. Great Plains cropping systems of the future will not only need to take advantage of crop sequences through synergism, but also take advantage of the interactions associated with diversity in space (polyculture).