Evaluating the management strategies and environmental benefits of intercropping maize within a Kura clover living mulch

Abstract

Intensive modern agriculture practices are known to be a primary driver of local and regional environmental degradation, where soil conditions before planting of conventional row crops are prone to erosion by water and wind and result in reduced soil fertility and nutrient loss. Kura clover (Trifolium ambiguum M. Bieb) as a living mulch has demonstrated a multitude of environmental benefits, and has potential for crop production systems in upper Midwest agricultural landscapes. This research evaluated the agronomic performance and environmental benefits of a Kura clover living mulch (KCLM) system intercropped with maize (Zea Mays L.) to develop management guidelines for upper Midwest KCLM systems.Evaluation of management strategies for an intercropped maize-KCLM system were conducted from 2022 to 2024 at sites in Rosemount and Lamberton, Minnesota, and assessed interactions among three maize planting dates (early, mid, late), two row establishment methods (banded herbicide and strip till), and five fertilizer nitrogen (N) rates (0-224 kg N ha-1) on maize yield and nitrogen uptake efficiency indicators in a KCLM system. Additionally, a one-year case study conducted at the Lamberton site assessed a landscape modified with subsurface tile drainage under a KCLM system to a control treatment of conventionally managed maize. The best management strategy for crop yield was found to be a banded herbicide (BH) row establishment paired with early (T1) to mid (T2) planting dates. The greatest average yields under an earlier planted BH treatment were produced by fertilizer N rates up to 180 kg N ha-1. Environmental conditions strongly influenced maize yield performance, where drought conditions in 2022 and 2023 led to yields 43.7% and 68.6% below county averages at the Rosemount site, respectively. In 2024, a 100%+ increase in rainfall at both sites likely helped to produce above county average maize grain yields under the T1/T2 BH treatments. Higher N uptake and partial factor productivity (PFP) values were observed under BH treatments and T2 planting dates, and were optimal at the 180 kg N ha-1 fertilizer rate. Environmental conditions may have constrained the ability of maize to access N, as recovery efficiency (RE) and agronomic efficiency (AE) values were not statistically significant. Nitrogen response curves demonstrated an upper limit in years of sufficient precipitation, while yield typically increased with higher N rates in drought years. Consistently superior performance of T1/T2 BH treatments with fertilizer N rates of 180 kg N ha-1 have proven to be resilient under variable environmental conditions and provide the best yield in a maize-KCLM system. Water discharge, NO3-N concentration, and NO3-N load were measured between April and August in 2024 at the KCLM plots in Lamberton, and compared to a control plot of conventionally managed maize. The KCLM treatment showed lower mean values for water yield, NO3-N concentration, and loading compared to the control treatment, but these differences were not statistically significant. The observation of lower mean values for NO3-N concentration and load are in agreement with prior studies and may suggest a potential trend toward reduced nitrate leaching and flow using KCLM in tile drained systems. High variability, environmental factors, and a limited number of observations and replicates constrains the statistical analysis and interpretation of results from this study, but can provide valuable insight and support previous findings from long-term research that similarly investigated the environmental benefits of implementing KCLM into intensified agricultural landscapes.