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

Program, 1990; Mitchell et al., 1999). Mitchell et al. (1999) also reported a perceived decline in soil quality The high-value, large-scale crop production systems in the San among producers. As a result of these concerns, many Joaquin Valley (SJV) of California typically entail intensive tillage and large fertilizer and water inputs but few C additions to the soil. SJV producers have begun to question the long-term Such practices often contribute to a decline in soil quality. Our objecsustainability of their intensively managed agricultural tive for this participatory study was to examine the effects of supplesystems. mental C management practices (SCMPs) on various soil quality To help farmers in the SJV evaluate the soil quality indicators. To increase farmer participation, we conducted the study effects of alternative soil management practices, the West on farms using a variety of SCMPs, including cover crops, compost and Side On-Farm Demonstration Project (WSD) was conmanure amendments, and several different crop rotations common ducted from 1995 to 1998. This participatory research to the region. The SCMPs significantly changed a number of soil and extension program originally included 11 large-scale properties, including soil organic matter (SOM); total Kjeldahl N; SJV row-crop producers, University of California Coopmicrobial biomass C and N; exchangeable K; Olsen P; and extractable erative Extension researchers, USDA Natural Resources Fe, Mn, and Zn. A comparison including previously established, adjacent organic, conventional, and transitional fields in addition to the Conservation Service (NRCS) conservationists, USDAtreatment fields at one farm revealed significant differences in 16 of ARS scientists, and private-sector consultants. 18 soil quality indicators. A soil quality index computed for this farm Developing science-based guidelines to quantify imscored the established organic system significantly higher than the pacts of routinely used organic inputs in this region was conventional system. Our results suggest that significant changes in identified as an important priority among the project’s several soil quality indicators occur with a variety of SCMPs. This is farmer participants (Mitchell and Goodell, 1996). A especially noteworthy considering the intensive tillage, irrigation, and brief, written survey of 15 participants, conducted durhot, semiarid environment of the SJV, California, where increases in ing a routine project meeting, invited input about their SOM and related soil properties are generally not expected in a 3-yr interest in an indexing tool to evaluate soil quality (sensu study. Andrews and Carroll, 2001; Karlen et al., 1998). Fourteen of the respondents indicated that a soil quality assessment tool would be useful to compare manageW Fresno County in the San Joaquin Valley ment alternatives (one blank response) (S.S. Andrews, (SJV) of California is one of the world’s most J.P. Mitchell, and D.L. Karlen, unpublished data, 1999). productive agricultural regions. Farmers in this area Based on that level of participatory support, our project produce more than one-third of the county’s annual $3 objectives were to (i) facilitate information exchange billion agricultural output, making it the highest reveamong farmers, consultants, and researchers regarding nue-producing county in the USA (California Dep. of these soil management practices; (ii) monitor and evaluFood and Agric., 1997). Dominant crop rotations inate on-farm, side-by-side comparisons of various SCMPs; clude annual crops (Mitchell et al., 1999) such as proand (iii) demonstrate the use of a soil quality index cessing tomato (Lycopersicon esculentum L.), cotton (SQI) for the region. (Gossypium hirsutum L.), onion (Allium cepa L.), garlic (A. sativum L.), cantaloupe (Cucumis melo L. var. reticulatus Naud.), wheat (Triticum aestivum L.), sugarbeet MATERIALS AND METHODS (Beta vulgaris L.), and lettuce (Lactuca sativa L.). Site Descriptions The intense production practices used in this region Side-by-side comparisons of conventional and organicinclude frequent and intensive tillage, irrigation, and based production systems were established on 11 farms in extensive use of fertilizers and pesticides but few addiautumn 1995. The farms were located in the western SJV tions of organic amendments to the soil (Mitchell et al., between Mendota and Huron, CA. At the beginning of the 1999). These intensive practices have raised concerns project, we randomly designated adjacent fields at each farm about resource management and water consumption as to receive either conventional or alternative treatments. The well as environmental concerns such as fugitive dust, fields varied in size but generally ranged from 30 to 60 ha ground water quality, and food safety (SJV Drainage Abbreviations: BD, bulk density; CEC, cation exchange capacity; S.S. Andrews and D.L. Karlen, USDA-ARS, Natl. Soil Tilth Lab., EC, electrical conductivity; MBN, microbial biomass nitrogen; MDS, Ames, IA 50011; J.P. Mitchell and T.K. Hartz, Dep. of Vegetable minimum data set; NRCS, Natural Resources Conservation Service; Crops and Weed Sci., and W.R. Horwath, G.S. Pettygrove, and K.M. PC, principal component; PCA, principal component analysis; PMN, Scow, Dep. of Soils and Biogeochem., Univ. of California, Davis, CA potentially mineralizable nitrogen; SAFS, Sustainable Agriculture 95616; R. Mancinelli, Dep. of Crop Prod., Univ. of Tuscia, 01100, Farming Systems (Project); SAR, sodium adsorption ratio; SCMPs, Viterbo, Italy; and D.S. Munk, Univ. of California Coop. Ext., 1720 supplemental carbon management practices; SJV, San Joaquin Valley; S. Maple Ave., Fresno, CA 93702. Received 22 May 2000. *CorreSOM, soil organic matter; SQI, soil quality index; TKN, total Kjeldahl sponding author (andrews@nstl.gov). nitrogen; WSA, water-stable aggregates; WSD, West Side On-Farm Demonstration Project; x-K, exchangeable potassium. Published in Agron. J. 94:12–23 (2002).