Cropping sequence diversification provides a systems approach to reduce yield variations and improve resilience to multiple environmental stresses. Yield advantages of more diverse crop rotations and their synergistic effects with reduced tillage are well documented, but few studies have quantified the impact of these management practices on yields and their stability when soil moisture is limiting or in excess. Using yield and weather data obtained from a 31-year long term rotation and tillage trial in Ontario, we tested whether crop rotation diversity is associated with greater yield stability when abnormal weather conditions occur. We used parametric and non-parametric approaches to quantify the impact of rotation diversity (monocrop, 2-crops, 3-crops without or with one or two legume cover crops) and tillage (conventional or reduced tillage) on yield probabilities and the benefits of crop diversity under different soil moisture and temperature scenarios. Although the magnitude of rotation benefits varied with crops, weather patterns and tillage, yield stability significantly increased when corn and soybean were integrated into more diverse rotations. Introducing small grains into short corn-soybean rotation was enough to provide substantial benefits on long-term soybean yields and their stability while the effects on corn were mostly associated with the temporal niche provided by small grains for underseeded red clover or alfalfa. Crop diversification strategies increased the probability of harnessing favorable growing conditions while decreasing the risk of crop failure. In hot and dry years, diversification of corn-soybean rotations and reduced tillage increased yield by 7% and 22% for corn and soybean respectively. Given the additional advantages associated with cropping system diversification, such a strategy provides a more comprehensive approach to lowering yield variability and improving the resilience of cropping systems to multiple environmental stresses. This could help to sustain future yield levels in challenging production environments.

Maximizing the environmental and economic benefits of cover crops partially depends on an accurate estimate of the N fertilizer requirement of subsequent crops. Four trials involving cover crop, tillage, and N rate variables were conducted from 1992 to 1995 in southcentral Ontario on well‐drained Typic Hapludalf soils. Rye (Secale cereale L.), oilseed radish [Raphanus sativus (L.) var. oleiferus Metzg (Stokes)], oat (Avena sativa L.), and red clover (Trifolium pratense L.) cover crops were established after winter wheat (Triticum aestivum L.) to evaluate their effects on soil NO3–N levels as well as subsequent corn (Zea mays L.) grain yield response at fertilizer rates of 0 and 150 kg N ha−1. Corn response to cover crops was compared in autumn plow and no‐till tillage systems. Within no‐till, autumn vs. spring chemical kill for red clover and rye was also evaluated. Although red clover biomass N yields were usually at least double those with other cover crops, all cover crops were equally effective at lowering residual soil NO3–N concentrations following wheat harvest. Presidedress NO3–N concentrations after autumn‐killed or plowed red clover were at least 24% higher than after any other cover crop. Grain corn yield responses indicated that red clover substantially enhanced N availability to corn in both autumn plow and no‐till systems, but that oilseed radish, oat, and rye cover crops did not enhance N availability to succeeding corn, compared with the no‐cover treatment, in either tillage system. Furthermore, the presidedress NO3–N test reliably estimated N fertilizer requirements of corn following all cover crop systems except spring‐killed red clover.

Potential benefits associated with establishing cover crops, such as reduced NO3 leaching risk and lower fertilizer N requirements for succeeding crops, will be fully realized only when the cover crop N contribution is accurately accounted for and availability is synchronous with succeeding crop N demands. The objectives of this study were to evaluate spring soil NO3−N accumulation patterns and N availability to corn (Zea mays L.) following annual ryegrass (Lolium multiflorum L.), oilseed radish [Raphanus sativus (L.) var. oleiferus (Stokes) Metzg.], red clover (Trifolium pratense L.), and no cover crop established after either winter wheat (Triticum aestivum L.) or barley (Hordeum vulgare L.). The wheat and barley were produced with 0.5, 1.0, and 2.0 times the amount of recommended N fertilizer. Six field trials were conducted on well‐drained Typic Hapludalf soils in southwestern Ontario intermittently from 1989 to 1995. Corn was produced using a spring mulch‐till system with only 10 kg ha−1 of fertilizer N, which was applied as part of the P starter fertilizer. Applying more fertilizer N to the previous year's small‐grain crop rarely increased spring soil NO3−N concentrations or corn yields. Soil NO3−N concentration increases between the May and June sample dates following annual ryegrass and oilseed radish did not differ substantially from where a cover crop had not been established; following red clover, however, NO3−N increases were always at least 2.8 times greater than after no cover crop. Average aboveground corn biomass N at anthesis following annual ryegrass was 25.6 kg ha−1 less than when no cover crop was grown, whereas following red clover it was 40.4 kg ha−1 greater than with no cover crop. Corn yields were consistently the highest following red clover and often the lowest following annual ryegrass; yield response was positively correlated with June soil NO3−N concentrations (r = 0.61‐0.93). These results suggest that N availability to succeeding corn differs among the cover crop treatments evaluated in the order red clover > oilseed radish ≥ no cover crop > annual ryegrass.

Abstract:In light of the environmental challenges ahead, resilience of the most abundant field crop production systems must be improved to guarantee yield stability with more efficient use of nitrogen inputs, soil and water resources. Along with genetic and agronomic innovations, diversification of northern agro-ecosystems using inter-seeded legumes provides further opportunities to improve land management practices that sustain crop yields and their resilience to biotic and abiotic stresses. Benefits of legume cover crops have been known for decades and red clover (Trifolium pratense) is one of the most common and beneficial when frost-seeded under winter wheat in advance of maize in a rotation. However, its use has been declining mostly due to the use of synthetic fertilizers and herbicides, concerns over competition with the main crop and the inability to fully capture red clover benefits due to difficulties in the persistence of uniform stands. In this manuscript, we first review the environmental, agronomic, rotational and economical benefits associated with inter-seeded red clover. Red clover adaptation to a wide array of common wheat-based rotations, its potential to mitigate the effects of land degradation in a changing climate and its integration into sustainable food production systems are discussed. We then identify areas of research with significant potential to impact cropping system profitability and sustainability.

Wheatimproves nitrogen use efficiency of maize and soybean-based cropping systems.