Cropping systems sustainable intensification refers to increased production per unit of land area without affecting system future capacities. It seeks to increase resource productivity by increasing the yield of a single crop or by intensifying crop sequence in the field. Since soybean has a reputation for yield plasticity, many agriculturalists have targeted soybean as a vehicle to incorporate ecosystem services through cover crops or additional economic returns through double cropping. Cover cropping is one of the most promising conservation practices with multiple benefits for production systems. Nevertheless, the adoption of cover crop/soybean sequence is still relatively low among MN farms due to cost or risk. Farmers require economically-viable solutions for production; therefore, further intensification by utilizing the double cropping system may provide another intensification alternative for Minnesota farmers. Unfortunately, nearly all the research effort has focused on the cover crop or the double crop with little research effort on the soybean piece of the pie. Broadly, the result is either disappointing soybean yields or highly erratic ones that range from very respectable to near failures. This research is intended to refocus attention on the primary cash crop – soybean – to identify combinations of cultural practices that minimize risk of yield loss. Once we have identified best management practices (BMPs) for the soybean portion of these intensification systems, we can truly assess the gains or losses in total soybean production that will result from their wide use. The questions we want to address are: What is the highest soybean yield that farmers can attain under these intensified systems after adjusting soybean management? and Is there a realistic opportunity to successfully incorporate some of these systems on our farms?
One of the main challenges for soybean in these intensification alternatives compared with the sole crop is the delay in planting date. In Minnesota, soybeans maintain nearly all of their yield potential when planted up until mid-May. Yield loss per day of delay increases progressively after that time. Soybean crops following cover crops frequently are planted after the end of this window due to planting delays or while waiting for biomass accumulation in the cover crop. In the case of soybean following winter barley, the planting date would be delayed until the end of June and even later than that following winter wheat. Normally-adapted varieties may find a mismatch between their most critical period for yield accrual and the shortened summer environment. Therefore, it is recommended that producers adjust varieties toward shorter maturities with lower risk, but correspondingly lower yield potentials.
On the other hand, planting delay exposes crops to conditions that hasten vegetative development. Delayed planting affects the capacity of the crop to reach full radiation interception (soil coverage) before the beginning of the critical stages (Monzon et al., 2021). This would be especially relevant in the case of early maturity varieties with an intrinsic shorter duration of the stage. Reduction in row spacing proved to be a useful management practice that increased the capacity of the crop to intercept radiation (Calviño et al., 2001). Thus, for those cropping systems that require a reduction in soybean maturity rate, we also expect that a reduction in the row spacing will increase soybean yield, biomass production, and yield stability across years.
Ultimately, we propose to assess the effect of soybean maturity rating and row spacing on soybean yield for different intensification alternatives. The question to answer is: Which are the maturity rating and row spacing combinations that maximize soybean yield for each cropping system (i.e., cover crop and double crops)? In order to answer this question, we propose to conduct field experiments in combination with simulation work to extrapolate our results to different locations and future years.