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On-Farm Assessment of Soil Quality in California's Central Valley

^a USDA-ARS, Natl. Soil Tilth Lab., Ames, IA 50011
^b Dep. of Vegetable Crops and Weed Sci., Univ. of California, Davis, CA 95616
^c Dep. of Soils and Biogeochem., Univ. of California, Davis, CA 95616
^d Dep. of Crop Prod., Univ. of Tuscia, 01100, Viterbo, Italy
^e Univ. of California Coop. Ext., 1720 S. Maple Ave., Fresno, CA 93702

* Corresponding author (andrews{at}nstl.gov)

Received for publication May 22, 2000. The high-value, large-scale crop production systems in the San Joaquin Valley (SJV) of California typically entail intensive tillage and large fertilizer and water inputs but few C additions to the soil. Such practices often contribute to a decline in soil quality. Our objective for this participatory study was to examine the effects of supplemental C management practices (SCMPs) on various soil quality indicators. To increase farmer participation, we conducted the study on farms using a variety of SCMPs, including cover crops, compost and manure amendments, and several different crop rotations common to the region. The SCMPs significantly changed a number of soil properties, including soil organic matter (SOM); total Kjeldahl N; microbial biomass C and N; exchangeable K; Olsen P; and extractable Fe, Mn, and Zn. A comparison including previously established, adjacent organic, conventional, and transitional fields in addition to the treatment fields at one farm revealed significant differences in 16 of 18 soil quality indicators. A soil quality index computed for this farm scored the established organic system significantly higher than the conventional system. Our results suggest that significant changes in several soil quality indicators occur with a variety of SCMPs. This is especially noteworthy considering the intensive tillage, irrigation, and hot, semiarid environment of the SJV, California, where increases in SOM and related soil properties are generally not expected in a 3-yr study.

Abbreviations: BD, bulk density • CEC, cation exchange capacity • EC, electrical conductivity • MBN, microbial biomass nitrogen • MDS, minimum data set • NRCS, Natural Resources Conservation Service • PC, principal component • PCA, principal component analysis • PMN, potentially mineralizable nitrogen • SAFS, Sustainable Agriculture Farming Systems (Project) • SAR, sodium adsorption ratio • SCMPs, supplemental carbon management practices • SJV, San Joaquin Valley • SOM, soil organic matter • SQI, soil quality index • TKN, total Kjeldahl nitrogen • WSA, water-stable aggregates • WSD, West Side On-Farm Demonstration Project • x-K, exchangeable potassium

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