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Nutrient Management Research Database
General Information
Research Title
Changes in soil chemical properties resulting from organic and low-input farming practices
Research Specifications
Crop: Tomato, Wheat, Safflower, Bean, Corn
Soil Type: Reiff Loam, Yolo Silt Loam
County, State: Yolo, California
Year: 1998
Authors
Clark, M.S., Horwath, W.R., Shennan, C., Scow, K.M.
Summary/Abstract from Original Source
Soil chemical properties during the transition from conventional to organic and low-input farming practices were studied over 8 yr in California's Sacramento Valley to document changes in soil fertility status and nutrient storage. Four fanning systems differing in crop rotation and external inputs were established on land previously managed conventionally. Fertility in the organic system depended on animal manure applications and winter cover crops; the two conventional systems received synthetic fertilizer inputs; the low-input system used cover crops and animal manure during the first 3 yr and cover crops
and synthetic fertilizer for the remaining 5 yr. At 4 and 8 yr after establishment, most changes in soil chemical properties were consistent with predictions based on nutrient budgets. Inputs of C, P, K, Ca, and Mg were higher in the organic and low-input systems as a result of manure applications and cover crop incorporations. After 4 yr, soils in the organic and low-input systems had higher soil organic C, soluble P, exchangeable K, and pH. Ceasing manure applications in the low-input system in Year 4 resulted in declining levels of organic C, soluble P, and exchangeable K. Crop rotation (the presence or absence of corn) also had a significant effect on organic C levels. Differences in total N appeared to be related in part to inputs, but perhaps also to differing efficiency of the farming systems at storing excess N inputs: the low-input system appeared to be most efficient,
and the conventional systems were least efficient. Electrical conductivity (EC), soluble Ca, and soluble Mg levels were tightly linked but not consistently different among treatments. Relatively stable EC levels in the organic system indicate 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 pools of stored nutrients, which are critical for long-term fertility maintenance.
Research Highlights
Design and Methods
The Sustainable Agriculture Farming Systems (SAFS) project consists of four farming system treatments consisting of crop rotations and the use of external inputs, including 4 year roations under conventional, low-input and organic management and a 2 year conventional rotation.
- All 4 year rotations include processing tomato, safflower, bean, and corn.
- In the Conv-4 treatment, bean is double-cropped with winter wheat; in the low-input and organic treatments, bean follows a biculture of oat (Avena sativa L.) and vetch (Vicia spp.).
- The Conv-2 treatment is a tomato and wheat rotations.
- There are four replications of each treatment and 56 subplots (67 by 18m) within these treatments arranged in a randomized block, split-plot design.
- Conventional treatments are managed with practices typical of the surrounding area.
- In the low-input system, fertilizer and pesticide inputs are reduced by using legume cover crops and manure.
- The organic system is managed with legume and grass cover crops and mixtures, composted animal manure, mechanical cultivation and limited use of CCOF approved pest control.
- Soil samples were taken at the time of plot establishment, after the first 4-yr rotation and after the second 4-yr rotation and analyzed for chemical properties.
- Nutrient budgets for each farming system were calculated for the period from 1989 to 1996, based on elemental inputs and outputs.
- Inputs were estimated from fertilizer and manure applications, estimates of contribution by legumes, cover crop biomass and previous cash crop residue.
- Ouputs were derived from cash crop yields and their nutrient concentrations.
- The nutrient budgets were then compared with measured soil properties.
Results
- Organic C levels increased in the organic, low-input, and Conv-4 systems between 1988 and 1992 by 19, 19 and 10%, respectively, but remained constant in the Conv-2 system.
- This resulted in significantly higher organic C levels in the organic and low-input systems.
- pH levels of all systems increased from 1988 to 1992.
- Soluble P was significantly greater in the organic system than in the Conv-2 and low-input systems at 15 to 30 cm.
- In 1996 Soluble P and pH were significantly greater in the low-input and organic systems than in the conventional systems.
- EC, soluble Ca and soluble Mg were significantly greater in the conventional systems.
- Exchangeable K was significantly higher in the organic system compared with all others.
- In 1996 the organic system had significantly greater total soil C compared with the conventional systems at 0 to 30 cm depths, while the Conv-4 system had significantly higher organic C compared with the other three systems in the 15 to 30-cm soil depth.
- Most changes in soil chemical properties were largely explained by differences in inputs.
- Higher inputs of C, N, P, and K led to higher soil organic C and N, soluble P, and exchangeable K in the organic farming system.
- The low-input system seemed the most efficient at storing excess N, with the conventional systems being the least efficient.
- Manure inputs were important in increasing organic C in organic and low-input systems.
Additional Information
Tags (links to other subject matter in database)
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