Daniel S. Munk

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

Relationships between remotely sensed reflectance data and cotton growth and yield.

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).

Conservation tillage and cover cropping influence soil properties in San Joaquin Valley cotton- tomato crop

Remotely sensed electromagnetic reflectance data can provide at relatively low cost a set of detailed, spatially distributed data on plant growth and development. Vegetation indices based on algebraic combinations of different wavelength bands are especially useful in summarizing reflectance data. One of the most commonly used vegetation indices is the normalized difference vegetation index, or NDVI. The objective of this study was to determine whether measurements based on the NDVI could provide information useful for site-specific management of cotton. Aerial photographs were taken of replicated Acala cotton field experiments in California in which the treatment was water or nitrogen stress level. NDVI integrated over time showed a significant correlation with lint yield in those experiments in which there was a significant stress effect on yield. The spatiotemporal pattern of NDVI reflected stress factors and was approximately coincident with the onset of measurable water stress. NDVI tended to indicate the presence of nitrogen stress even in those cases where the stress did not result in a significant yield reduction. In a study of the correlation of NDVI with late season plant mapping indices NDVI was correlated with nodes above white flower and strongly correlated with nodes above cracked boll. An alternative vegetation index, the relative nitrogen vegetation index, was not better than NDVI as an indicator of nitrogen stress.

A qualitative simulation model for cotton growth and development

Following 4 years of a cotton-tomato rotation on the west side of the San Joaquin Valley, conservation tillage and cover crops altered physical and chemical properties of soil. In conservation tillage systems, bulk density decreased and available concentrations of nitrate and phosphorus increased. In contrast, the conservation tillage system redistributed potassium to the surface of the soil, lost organic matter and increased salt concentrations, all potentially detrimental to plant growth. Cover cropping, on the other hand, increased soil organic matter regardless of the tillage treatment, and increased potassium concentrations. By cover cropping, farmers in this region may improve their soil quality; however, the benefits of conservation tillage to soil quality are fewer and will require more research to determine long-term effects.

Subsurface Drip and Overhead Irrigation Effects on Conservation-tilled Cotton in the San Joaquin Valley

Qualitative simulation models use variables that take on categorical rather than continuous values. Qualitative models for crop growth may serve as useful alternatives or complements to traditional crop growth models. The objective of this study was to demonstrate the development and use of a methodology for constructing qualitative crop models. We developed and tested a qualitative simulation model for the growth and development of Acala cotton in the San Joaquin Valley, California. The model is based on a logical description of cause and effect, and on the comparison of input data with projected solutions. The simulation contains eight time stages, ranging from crop emergence to late-season production of fruiting structures. Implementation of the model requires that it be calibrated, verified, and validated. Procedures for carrying out these operations are described. The model is tested by comparison with field data from soils at different salinity levels, and it provides reasonable predictions of the observed data. Thus, the development of qualitative simulation models for crop production appears feasible. These models may be useful as components of crop management decision support systems.

Impact of Early Defoliation on California Pima Cotton Boll Opening, Lint Yield, and Quality

Conservation cropping systems are being developed for cotton (Gossypium spp.) traditionally grown on raised beds with several soil-disturbing tillage passes in the San Joaquin Valley (SJV) of California, USA. Overhead (OH) irrigation and subsurface drip irrigation (SSDI) systems are water-conserving techniques being tested with reduced tillage in the SJV. However, crop growth, yield, microclimate, and pest population dynamics in these systems have not been documented. A field study was conducted in 2011 and 2012 at Five Points, Calif., to evaluate the difference between the two irrigation systems. Cotton cv. Phytogen 725 RF was no-till planted into wheat residue. In both years, the soil surfaces in the OH plots were 1° to 2°C cooler and 5% to 15% wetter than the SSDI plots. These differences had no effect on crop growth, development, yield, or quality, but weed densities and biomass were lower in the SSDI than in the OH in both years. However, the SSDI plots had more spider mites (Tetranychus sp.) than the OH plots in 2011. The study showed that cotton could be successfully grown with conservation tillage, high residue systems, with either OH or SSDI systems in the SJV.

Response of Acala Cotton to Nitrogen Rates in the San Joaquin Valley of California

Chemical defoliation is a necessary pre-harvest practice in Pima cotton (Gossypium barbadense L.) production in California. Growers begin defoliating as early as possible but yield and quality loss can occur if the bolls are not fully mature. Harvest aids can advance harvest dates, avoid late-season pests, and adverse weather conditions in California. A study was conducted on Pima cotton, cv. ‘Phytogen-802’. Different rates of Ginstar (ai thidiazuron/diuron, Bayer CropScience) or Ginstar plus Finish 6-Pro (ai ethephon/cyclanilide, Bayer CropScience) were applied at 6 to 7 nodes above cracked boll (NACB) or 4 to 5 NACB at various rates. Results showed that these harvest aids could be applied at the tested rates at both timings without any adverse effects on percent open bolls, and lint yield and quality. Therefore, application of these harvest-aid materials starting at 6 to 7 NACB can benefit Pima cotton growers in California as early harvests can be achieved without compromising lint yield or quality.

No-tillage and high-residue practices reduce soil water evaporation

The responses of Acala cotton (Gossypium hirsutum L.) in California to a range of applied nitrogen (N) treatments were investigated in a 5-year, multisite experiment. The experiment’s goals were to identify crop growth and yield responses to applied N and provide information to better assess the utility of soil residual N estimates in improving fertilizer management. Baseline fertilizer application rates for the lowest applied N treatments were based on residual soil nitrate-N (NO3-N) levels determined on soil samples from the upper 0.6 m of the soil collected prior to spring N fertilization and within 1 week postplanting each year. Results have shown positive cotton lint yield responses to increases in applied N across the 56 to 224 kg N/ha range in only 41% (16 out of 39) of test sites. Soil NO3-N monitoring to a depth of 2.4 m in the spring (after planting) and fall (postharvest) indicate most changes in soil NO3 occur within the upper 1.2 m of soil. However, some sites (those most prone to leaching losses of soluble nutrients) also exhibited net increases in soil NO3-N in the 1.2- to 2.4-m depth zone when comparing planting time vs. postharvest data. The lack of yield responses and soil NO3-N accumulations at some sites indicate that more efforts should be put into identifying the amount of plant N requirements that can be met from residual soil N, rather than solely from fertilizer N applications.