Fine root production and decomposition of integrated plants under intensified farming systems in Brazil

Abstract

To ensure food security, foster agri-environmental sustainability, and prevent agricultural expansion into preserved areas, it is imperative to intensify plus diversify agriculture within integrated farming systems in the coming decades. Maximizing productivity and carbon sequestration through such systems demands understanding below-ground interactions and further research into plant root dynamics, which have often been neglected or overlooked. This study examined the effects of integrated farming systems, specifically crop-livestock and crop-livestock-forestry, on fine-root dynamics of crops and pastures (i.e., herbaceous plants). Using an extensive grazing pasture as a control, and intensification through crop-livestock and crop-livestock-forestry, we aimed to evaluate if integrated systems (i) enhance herbaceous root growth and necromass addition, and (ii) accelerate root turnover. We also investigated whether multiple linear regression modeling could predict root production and decomposition using the edaphoclimatic variables monitored in the areas. Herbaceous fine-root dynamics were observed over two years using the minirhizotron technique. Installation involved five 70 cm-deep acrylic tubes in extensive grazing and crop-livestock and fifteen in crop-livestock-forestry (1.9, 4.3, and 7.5m tree inter-row distances). In integrated systems, annual corn cropping was succeeded by grazing on a palisadegrass pasture. The trial measured eight additional soil and climatic parameters for a regression model using a stepwise selection procedure, including average soil temperature, photosynthetically active radiation, available soil water, soil bulk density, soil pH, available soil phosphorus, the sum of soil bases, and cation exchange capacity. Extensive grazing accumulated 124.8 m m⁻² of roots, constituting 48% of crop-livestock (259.7 m m⁻²) and 66% of crop-livestock-forestry (189.5 m m⁻²). Root growth near Eucalyptus trees was reduced by 51% compared to crop-livestock. Root turnover followed the order of extensive grazing < crop-livestock < crop-livestock-forestry. The peak daily root productivity was from 31 to 80 days of the crop cycle when corn was intercropped with palisade grass in the integrated systems. Multiple regression models were superior for predicting root decomposition, reaching adjusted R² values of 0.81 and 0.71 for crop and pasture cycles, but were ineffective for root growth (R² < 0.25). Therefore, additional parameters are needed to fit the root growth accurately. We conclude that integrated farming enhances fine-root production and root necromass accrual, accelerating root cycling compared to extensive pasture. However, as introducing Eucalyptus in crop-livestock impairs herbaceous root development near trees, we recommend adjusting tree density and inter-row spaces to alleviate these adverse effects, especially for annual crop cultivations.