CHANGES IN SOIL CHEMICAL-PROPERTIES RESULTING FROM ORGANIC AND LOW-INPUT FARMING PRACTICES

Soil chemical properties during the transition from conventional to or ganic and low input farming practices were studied over 8 yr in Califo rnia's Sacramento Valley to document changes in soil fertility status and nutrient storage. Four farming systems differing In crop rotation and external Inputs vc cre established on land previously managed conv entionally. Fertility in the organic system depended on animal manure applications and winter cover crops; the two conventional systems rece ived synthetic fertilizer inputs; the low-input system used cover crop s and animal manure during the first 3 yr and cover crops and syntheti c fertilizer for the remaining 5 yr, At 4 and 8 yr after establishment , most changes in soil chemical properties were consistent with predic tions based on nutrient budgets. Inputs of C, P, K, Ca, and Mg were hi gher in the organic and low-input systems as a result of manure applic ations and cover crop incorporations. After 4 yr, soils in the organic and low-input systems Lad higher soil organic C, soluble P, exchangea ble K, and pH, Ceasing manure applications in the low-input system in Year 4 resulted in declining levels of organic C, soluble P, and excha ngeable K, Crap rotation (the presence or absence of corn) also had a significant effect on organic C levels. Differences in total N appeare d to be related in part to inputs, but perhaps also to differing effic iency of the funning systems at storing excess N inputs: the low-input system appeared to be most efficient, and the conventional systems we re least efficient. Electrical conductivity (EC), soluble Ca, and solu ble Mg levels were tightly linked but not consistently different among treatments, Relatively stable EC levels in the organic system indicat e that animal manures did not increase salinity. Overall, our findings indicate that organic and low-input farming in the Sacramento Valley result in small but important: increases in soil organic C and larger peals of stored nutrients, which are critical for long-term fertility maintenance.