Kidson, M.; Hernandez-Soriano, M. C.; Mndzebele, B.; Ndaba, B.; Adeleke, R.; Nciizah, A.; Roopnarain, A.

Reducing nitrogen (N) losses and associated nitrate (NO3-) leaching and nitrous oxide emissions from agricultural land is a critical target worldwide. This is particularly urgent in areas with low fertility soils and a climate that increases the risk of N loss, such as the arid and temperate regions of South Africa. Here, we assessed the potential of fodder oats (Avena sativa) as a winter catch crop to deplete residual N in a field laid fallow for the previous four years, where vetch had proliferated. The soil presented a high clay content (34-44%), with the main exchangeable bases being calcium and magnesium hence, ammonium (NH4+) deposited by the vetch was expected to be rapidly adsorbed and slowly released. A significant decrease in the concentrations of NO3- (49%) and NH4+ (30%) throughout the soil profile (0-90 cm) was observed following harvest of the oats compared to the concentrations measured before sowing. The effectiveness of the oats to uptake both forms of N from top and deep soil layers enhances their potential to reduce N losses. Our results are useful to fill current knowledge gaps on N dynamics in understudied, vulnerable soils such as agricultural land in South Africa, and to advance crop rotation strategies that reduce risk of N leaching.