Deliverable 1 – Identify the Best Cover Crops before Soybeans
Based on the results from Deliverable 2 & 3 (outlined below) we did not observe differences due to cover crop on soil health, hydraulic properties, or soybean yield that led to a conclusion of what the best cover crop(s) is for soybean production systems.
However, maximizing the utility and success of cover crops is a long-term proposition. It is not advisable to make concrete management decisions regarding the implementation of cover crops based on 1 year of data. If that were the case, the conclusion and recommendations of this research would be not to employ cover crops in soybean production systems due to added cost without a return on investment.
Deliverable 2 – Impact of Cover Crops on Soil Health and Hydraulic Properties
Data Taken
1) Gravimetric soil moisture content (0 – 2” and 0 – 4”) depths at V2 (2 trifoliates) and R6.5 (physiological maturity).
2) Bulk Density and Porosity of Soil (V2 & R6.5)
3) Soil Infiltration Rate (SIR) taken at V2
4) Plant Heights – R3 and R6.5
5) Stem Diameter – at harvest
Summary
Stand Counts
Stand counts were measured at 7, 14, 21, & 28 days after planting (DAP). At 7 DAP, the stand varied due to residue management, and was 10% more in plots where the residue had been removed the previous fall. At 28 DAP, stand counts varied due to cover crop and was only 58% of the seeding rate.
Cover crops and soil surface residue insulate the soil and help soils retain soil moisture longer into the spring. This results in soils that remain cooler for longer as well. However, soybean has a substantial amount of phenotypic plasticity, and this delay in stand establishment or potential decrease in final stand do not always negatively impact soybean yield.
Gravimetric soil moisture content (Og)
Og was measured in the spring (V2 growth stage) varied due to cover crop, and was greatest following cereal rye (27.6%). It was statistically similar to cosaque oat + crimson clover + forage radish (25.8%) and our 6-wax mix (25.6%), and at least 2.8% more than all other treatments. However, we observed no differences in soil water content at the deeper depth of 0 – 4”.
Cereal rye produces substantial above-ground biomass and upon chemical termination, produces a large amount of surface residue that “insulates” the soil surface and reduces the amount of water that evaporates from the upper soil profile. Cereal rye is an excellent scavenger of soil nitrogen, however, is not a concern in a soybean production system.
Gravimetric soil moisture content also varied when sampled at R6.5, but this time due to residue management. Plots where residue was not removed contained 3.45% more soil moisture from 0 – 2” than those where residue was removed. The removal of soybean residue post-harvest is not a commonly utilized agronomic practice in soybean production systems. However, this provides value in our research by allowing us to quantify the impact that soybean residue has on these factors.
Bulk Density and Soil Porosity
Bulk density and soil porosity were both measured at V2 and again at R6.5 in the uppermost 2” of the soil profile. We observed no differences due to cover crop or residue management in 2024 at either of these sample timings. We believe that any changes in these soil properties will likely take multiple successive years of cover crops and the literature supports this conclusion.
Soil Infiltration Rate
Soil infiltration rate was measured at the V2 growth stage. While many studies have shown cover crops to improve soil infiltration, we did not observe any differences in this study. Many studies in the literature take soil infiltration measurements prior to cover crop termination. However, we wanted to evaluate the “in-season” impact of cover crops on infiltration and as such observed no differences. Again, we conclude that additional years of continuous cover cropping are likely necessary prior to seeing significant results in this category.