Mitigation of nitrogen and phosphorus leaching from black soil croplands in Northeast China

Black soil (Mollisol) is a fertile and productive soil type found in Northeast China and is important for China's maize production. Large amounts of synthetic fertilizers are applied to meet the increasing cereal production demands but have low efficiency, leaving excessive nitrogen and phosphorus in the soil. This excess increases the risk of agricultural nonpoint pollution, black soil degradation, and surface/underground water pollution, threatening drinking water security. Studies conducted in the black soil region indicate that nitrogen and phosphorus leaching intensities are lower in the cereal croplands than in the other regions, especially those in the North China Plain. However, residual nitrogen and phosphorus remaining in soils owing to high fertilizer application levels increase the leaching potential, especially with intense precipitation. Environmental factors and field management practices were analyzed to identify effective control measures for nitrogen and phosphorus leaching and propose leaching reduction strategies for rain-fed maize and vegetation fields in the black soil region. Fertilization and precipitation are the primary drivers of nitrogen and phosphorus leaching in cultivated black soils, and irrigation is correlated to leaching intensity in vegetation fields. New strategies should be adopted to mitigate leaching, such as setting maximum fertilizer thresholds based on crop demands, adjusting fertilization timing to avoid high precipitation seasons, and using water-saving irrigation. Replacing synthetic fertilizer with manure, combining inorganic and organic fertilizers, and using no-tillage with maize stover mulching, crop rotations, and biochar are other field management practices to reduce the nitrogen and phosphorus pollution risk. In the maize croplands, only basal fertilizer should be applied during the growing season, an organic and synthetic fertilizer combination (50%-70% organic) should be used, and no-tillage with maize stover mulching should be considered to control the nitrogen and phosphorus leaching intensities. Reducing fertilizer amounts and irrigation water use by 20% and deeply burying the crushed straw after the autumn harvest are also recommended for vegetation fields. Practical strategies for nitrogen and phosphorus pollution prevention are important for sustainable agricultural development and maintenance in the black soil region.