Management duration controls the synergistic effect of tillage, cover crop, and nitrogen rate on cotton yield and yield stability

Authors: NOURI, AMIN - University Of Tennessee; LEE, JAEHOON - University Of Tennessee; YODER, DANIEL - University Of Tennessee; JAGADAMMA, SINDHU - University Of Tennessee; WALKER, FORBES - University Of Tennessee; YIN, XINHUA - University Of Tennessee; Arelli, Prakash

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2020
Publication Date: 6/1/2020
Citation: Nouri, A., Lee, J., Yoder, D.C., Jagadamma, S., Walker, F.R., Yin, X., Arelli, P.R. 2020. Management duration controls the synergistic effect of tillage, cover crop, and nitrogen rate on cotton yield and yield stability. Agriculture, Ecosystems and Environment. https://doi.org/10.1016/j.agee.2020.107007.
DOI: https://doi.org/10.1016/j.agee.2020.107007

Interpretive Summary: The capacity of agricultural systems to maintain high and stable crop yields under weather variability, resource scarcity, and reduced fertilizer input has important implications for production costs, environmental health, and the security of food, feed, and fiber. However, little is known about the time span for interactions of no tillage and cover crops to achieve enhanced yield and yield stability while lowering nitrogen fertilization. The analyses of 33 years yield data, comparing sequential phases of roughly 10 years each, revealed a profound impact of management duration on cotton yield and yield stability from tillage, nitrogen fertilizer rate, and cover crop management systems. During phase 1 (the first 1 to 10-year period), cotton yield varied largely across 32 management systems. No yield and yield stability benefits were obtained by cover cropping or increased nitrogen rate, while conventionally tilled (CT) systems showed a greater mean cotton yield and yield stability compared to no tillage (NT) systems in phase 1. However, management durations beyond the initial 10 years and further beyond 20 years, resulted in greater and more temporally stable cotton yield as well as lower nitrogen requirement under NT than CT systems. The yield benefits of NT systems during the phases 2 and 3 were particularly evident in unfavorable environmental conditions. This result signifies the essential role of long-term NT management in enhancing agroecosystem resilience to uphold the productive functions under various environmental stresses. Long-term incorporation of legume species, especially hairy vetch further enhanced the yield potential of NT. However, optimum nitrogen adjusted for cover crop species and tillage was a key factor for achieving a higher yield stability. During phase 1, nitrogen rates greater than 34 to 67 kg ha-1 delivered no yield advantages, but considerably declined yield stability under legume cover crop species. During the phases 2 and 3, the greatest yield and yield stability benefit was associated with hairy vetch cover crop planted on NT system with 34 kg ha-1 nitrogen rate. The results support the hypothesis that long-term interaction between legume covers and NT not only increases yield outcome, but also improves the economic and environmental sustainability of agroecosystem by increasing yield stability and reducing the need for additional nitrogen fertilizer input. Despite the general trend of increasing yield along the experimental period, the rate of increase varied largely among management systems. Therefore, increase in management duration led to a more distinct differentiation of yield outcome among management systems. These results helped to better understand the effect of management duration on agronomic, economic, and environmental outputs of agroecosystems under different management practices. Additional analysis with a specific focus on productivity of different agronomic practices under extreme weather conditions can provide further insight into utility of these practices for mitigation of climatic stresses.

Technical Abstract: Resilient agroecosystems are foundational for stable and profitable food, feed, and fiber production in the face of increasing climatic perturbations and environmental stresses. Enhanced soil and environmental benefits of cover crops applied to conservation tillage systems has been well documented. However, little is known about the timespan for interactions of no tillage and cover crops to achieve enhanced yield and yield stability while lowering N fertilization. Using a long-term continuous cotton experiment in southeastern USA, we analyzed yield data collected from 1986 to 2018 from 32 management systems to identify how management duration controls the synergistic effect of applied mineral N rates (0, 34, 67, and 101 kg ha-1), cover crops (no cover [NC], hairy vetch [HV], crimson clover [CC], and winter wheat [WW]), and tillage practices (no tillage [NT] and conventional tillage [CT]) on cotton yield and yield stability. Yield stability was analyzed using Finlay—Wilkinson regression model, Wricke’s Ecovalance, and coefficient of variation, and a mixed model approach was used to compare the yield and yield stability within three time phases (1-10 years, 11–20 years, and 21-33 years) at the 95% confidence level. During the initial 10 yr period (phase 1) CT resulted in greater cotton yield (7%) and yield stability than NT. However, in phase 2 (11–20 years) and phase 3 (21-33 years) NT led to greater yield (7%) and yield stability for almost all cover crop × N interactions, except for zero N following NC and WW. Increased N during the initial phase reduced both yield and yield stability under legume cover crops. During phases 2 and 3, however, the higher N rates (67 and 101 kg N ha-1) increased cotton yield, although management systems with 0 and 101 kg N ha-1 showed the largest temporal yield variability. Legume cover crops increased yield and yield stability under low N rates. The maximum combined yield and yield stability benefit was obtained from HV cover on NT with additional application of 34 kg N ha-1. Our results suggest that after the initial phase NT delivers the most consistent yield benefits while enhancing yield stability against unfavorable environmental conditions. Long-term integration of legume cover crops (particularly HV) to NT systems was effective in maintaining high yield and increasing yield stability while lowering N rates.