Diversified legume-based crop rotations enhance nutrient cycling and long-term productivity in tropical no-tillage systems

Abstract

Diversified no-tillage crop successions are key strategies for improving soil health, productivity, and sustainability in tropical environments. However, adoption of diversified cropping systems remains limited due to economic, cultural, and technical constraints. This study aimed to evaluate how long-term diversified crop rotations, differing in legume inclusion and mineral phosphorus (P) and potassium (K) fertilization, influence system nitrogen (N), P, and K budgets, biomass production, and crop productivity in mature tropical no-tillage systems (NTS). Using a 10-year field experiment established on a tropical Ferralsol in southern Brazil, we evaluated six long-term crop rotations that differed in crop diversification, inclusion of Fabaceae cover crops, and phosphorus and potassium mineral fertilization. Total system N, P, and K budgets were quantified by integrating nutrient inputs, crop uptake, grain nutrient export, biomass nutrient cycling, and net soil nutrient balances. Intensive legume-based rotations increased crop productivity compared with low-diversity, non-legume rotations (specifically, the two-crop black oat/common bean succession). Vetch-based rotations under optimal or suboptimal mineral fertilization, as well as unfertilized vetch rotations, produced the highest cumulative grain yields (∼52,000 kg ha -1 ), representing a 38% increase (a 1.38-fold increase) over the black oat/common bean rotation (∼38,000 kg ha -1 ). This response was associated with a 40% increase in aboveground biomass and grain yield when maize followed hairy vetch rather than black oat. Legume-intensive rotations under optimal mineral fertilization or without fertilization maintained a strongly positive N budget (+559 kg ha -1 ), whereas the low-diversity black oat/common bean rotation showed a net N deficit. Conversely, all unfertilized systems, including the highly productive unfertilized hairy vetch-based rotations, exhibited strongly negative P and K budgets, indicating a progressive risk of soil fertility depletion. Only suboptimal mineral-fertilized vetch rotations partially offset these nutrient deficits in highly crop-productive systems. The study highlights the role of legume-based crop rotations as a key strategy to sustain a positive N budget, thereby supporting nutrient cycling and crop productivity under tropical NTS. Maintaining nutrient balance remained dependent on coupling biological N fixation with balanced mineral P and K fertilization to offset nutrient export deficits in high-yield systems and to reduce the risk of long-term soil fertility depletion.