Impact of cultural practices and organic amendments on soil fertility and crop yields in organic vegetable cropping systems

Organic agriculture promotes soil health through the use of cover crops, biological diversity, and plant- and animal-based amendments. Two concurrent field experiments examined effects of crop diversification on soil nutrients and crop yields. The study spanned two years and encompassed seven cropping systems with different cover crops and production intensities. Each system incorporated three crops annually: a summer cover crop followed by two cash crops, with cash crop rotations reversed during autumn and spring seasons. The least diverse system had no cover crop followed by monocultured vegetables. The more diverse systems included cover crop monocultures of grass-pearl millet (PM), sorghum sudangrass (SS), or legumes, sunn hemp (SH) and velvetbean (VB), followed by monocultured vegetables. In the most diverse systems cover crop bicultures of PM and SH (PMSH) and SS and VB (SSVB) were followed by vegetables intercropped with either living mulch or cash crop. Soil nutrient concentrations varied between cropping systems. P and Ca concentrations increased, while K decreased, over the experimental period. Soil Fe decreased over time in the grass and legume systems. PM and PMSH produced the largest cover crop biomass, with C:N ratios ranging from 23–43. Broccoli yields were unaffected by cover crop diversity. Squash yields were higher in grass systems when grown in the first year, while bell pepper yields were greater in biculture systems when grown in the second year. Sweet corn yields were highest in grass and legume systems. Cover crop-based systems require additional time and complementary strategies to enhance soil fertility and crop yields.