Conservation tillage is a crucial component of sustainable cropping systems. One of the key benefits of residue cover are reduced soil erosion and increased soil carbon, which is not only important for improving soil quality and crop productivity but also for mitigating climate change (Lal et al., 2007; Poffenbarger et al., 2017). Even though agro-ecosystem benefits are well established, some farmers remain hesitant to transition from conventional to conservation tillage. One of the obstacles of planting soybean into heavy corn residue is the potential for slower early growth and yield reductions compared to soybeans planted in conventionally tilled fields. Crop germination, emergence, and growth are primarily regulated by soil temperature, moisture, and nutrient availability to roots.

Mollisols, the dominating soil orders in north and central Illionis, generally have plenty of organic matter that mineralizes and provides crops with nitrogen (N) and sulfur (S). However, fine-textured soils with high organic matter also tend to be cooler and wetter early in the spring and around planting time. This limits mineralization, which in turn limits early-season N and S availability in the soil. This situation can be exacerbated in no-till and strip-till fields because the corn residue can tie up some of the early-season N that otherwise would be available for crop uptake. A recent study in Wisconsin reported significant yield increases (+4 bu/A) with pre-plant N application in no-till soybeans relative to no N (Kendall et al., 2023). In addition, the authors observed no yield difference between no-till with spring N and conventional tillage without N (64 vs. 66 bu/A, respectively). A lower early-season N and S availability is also expected in coarse-textured soils with low organic matter, such as Alfisols which are commonly found in southern Illinois. Studies in Indiana have shown significant yield increases (10-15 bu/ac) with S applications at planting time on sandy or coarse-texture soils with less than 2% organic matter (Shaun Casteel, personal communication).

While starter fertilizer is not widely used for soybean production, the reduced early-season nutrient availability warrants further evaluation in fields under conservation tillage (e.g., no-till and strip-till). With this practice, nutrients are applied near the seed at planting with the goal of increasing early-season plant growth and nutrient uptake. About 50-60% of the total N required by soybean crops is supplied by the biological N fixation (BNF) process, while the remaining comes from the pool of available N in the soil (Tamagno et al., 2018). Sulfur is a macro-nutrient that is needed as a co-factor for proper nodulation and fixation by Bradyrhizobium japonicum for soybean.

Row spacing is also an important practice in intensive management systems. Many studies have shown yield benefits when using narrow rows compared to 30-inch rows. Key benefits of narrow rows include early canopy closure that enables more light interception to drive photosynthesis, weed control, and reduced erosion.

Our overall goal with this research is to optimize soybean production in conservation tillage while conserving natural resources and enhancing environmental sustainability. The specific objectives are to 1) understand the mechanisms driving soybean growth and yield in conservation tillage systems (i.e., soil temperature, immobilization of N and S, delayed soybean development and nodulation/fixation), 2) evaluate the impacts of starter fertilization and row spacing on soybean nutrient uptake, seed yield, and seed quality, and 3) identify best management practices that optimize soybean production under conservation tillage.

This project will be conducted at 3-4 sites covering different soil types (e.g., Mollisols and Alfisols). Through soil and plant sampling, we will 1) evaluate how starter fertilization and tillage affect soybean growth, nutrient uptake, and seed yield and quality, 2) see how tillage and starter fertilizer might interact, and 3) assess the interaction of row spacing and fertilization in longer-term no-till cropping systems.

This research aims to benefit growers, agronomists, and state agricultural and environmental agencies by identifying the mechanisms that contribute to slower growth and reduced yield in conservation tillage systems. By identifying these trends, recommendations can be made to help maintain or improve soybean yield and quality, resulting in more sustainable production systems.