Tropical Grasses—Annual Crop Intercropping and Adequate Nitrogen Supply Increases Soil Microbial Carbon and Nitrogen

Abstract

In Brazil, grain crops in no-till soybean–maize succession have reduced biodiversity and carbon input into soil. Intercropping is a promising approach to address these problems. This study aimed to evaluate the microbiological quality of soil in conventional and intercropping systems in soybean–maize succession, depending on tropical grass and nitrogen fertilizer uses. The treatments were arranged in a randomized complete block design and a split plot scheme, with four replications. The main plots consisted of the following cropping systems: soybean monoculture–maize monoculture; soybean intercropped with Aruana Guinea grass (Megathyrsus maximum cv. Aruana)–maize intercropped with Aruana Guinea grass; and soybean intercropped with Congo grass (Urochloa ruziziensis cv. Comun)–maize intercropped with Congo grass. The subplots consisted of nitrogen rates (0, 50, 100, and 150 kg ha−1) applied as side-dressing in rows of maize and tropical grass in the autumn–winter season. Our results showed that maize or soybean intercropped with tropical grasses and adequate nitrogen rates favored the entry of microbial carbon and nitrogen, stimulated enzymatic activity, and reduced C-CO2 loss. However, the excess nitrogen supply can nullify the benefits of the intercropping systems. We concluded that the intercropping systems can improve soil microbiological quality in a short time with adequate nitrogen supply.