Long-term liming improves soil fertility and soybean root growth, reflecting improvements in leaf gas exchange and grain yield

Soil acidity is one of the major drivers of yield-limited crop productivity, particularly when combined with dry spells during crop development. Liming is a widely used strategy for alleviating the negative effects of soil acidity, ensuring greater crop root development to assist the plant in periods of low water availability, promoting full photosynthetic activity and, consequently, increasing crop yield. Here, we investigated the long-term effects of surface liming on soil chemical properties as well as soybean root growth, nutrition, photosynthetic parameters and grain yield during three growing seasons (2016-2019) in a region prone to dry spells. The long-term liming experiment was established in 2002. We evaluated the long-term effects of four surface lime rates: control, soil not treated with lime; 1/2 RLR, soil treated with half the recommended lime rate; 1 RLR, soil treated with the full recommended lime rate; and 2 RLR, soil treated with twice the recommended lime rate. The last lime application occurred in 2016. Our results revealed that increasing lime rates applied to soil surface up to 2 RLR increased soil fertility and root growth, besides to enhance the root distribution along soil profile. These changes contributed to boost soybean leaf photosynthetic pigments and gas exchange, leading to better growth, nutrition and grain yields, despite periods of dry spells. Our results suggested that in tropical agricultural systems with intensive cultivation throughout the agricultural year, higher lime rates can be applied without nutritional imbalances in the soil and plants. Our study provided important clues on how long-term liming changes soil fertility and triggers the cascading effects in improving root growth and distribution, as well as soybean photosynthetic metabolism and yield.