T.K. Hartz

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

On‐farm monitoring of soil and crop nitrogen status by nitrate‐selective electrode

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).

A quick test procedure for soil nitrate‐nitrogen

Abstract Nitrate‐nitrogen concentration in fresh petiole sap, as measured by a portable, battery‐operated, nitrate‐selective electrode, was highly correlated with NO3‐N concentration in dry petiole tissue of broccoli [Brassica oleracea L. (Italica group), r2 = 0.84], celery [Apium graveolens L. var. dulce (Mill.) Pers., r2 = 0.88], lettuce (Lacluca saliva L., r2 = 0.77), pepper (Capsicum annuum var. annuum L., r2 = 0.89), tomato (Lycopersicon esculentum Mill., r2 = 0.83), and watermelon [Citrulius lanatus (Thunb.) Matsum. & Nakai, r2 = 0.88]. This relationship was linear over a wide range of NO3‐N values and was generally unaffected by site, crop, cultivar, or growth stage, provided that petiole tissue analyzed was from recently matured leaves. Sap was analyzed directly without dilution or filtration. The slope of the regression equation differed widely among crops. Selective electrode analysis of NO3‐N concentration of soil solution samples obtained by suction lysimetry was also highly correlated with co...

Relationship between Soil Phosphorus Availability and Phosphorus Loss Potential in Runoff and Drainage

Abstract A procedure for extraction and measurement of nitrate‐nitrogen (NO3‐N) in soil is described. Extracting solution [0.025M Al2(SO4)3] and field‐moist soil are measured volumetrically, with NO3‐N concentration measured by nitrate‐sensitive colorometric test strips or nitrate‐selective electrode. Across a range of soil texture, moisture content, and NO3‐N concentration, the procedure was well correlated with conventional laboratory analysis of 2N KC1 soil extracts (r2 = 0.94). This quick test procedure is proposed as an on‐farm monitoring technique to improve N management.

Estimating soil potassium availability for processing tomato production

Abstract Elevated soil phosphorus (P) content is common in the central coastal valleys of California, the result of decades of the intensive vegetable production. Undesirably high P concentration in surface water in this region stimulated interest in evaluating techniques to rank the potential for soil P loss to the environment. Phosphorus availability of 25 representative soils from fields in vegetable rotations were evaluated by the following techniques: bicarbonate‐extractable P (Pbc)–calcium chloride, extractable P (Pcc), P extractable by iron‐impregnated paper (PFe), P extractable by anion exchange resin (Pae), and the degree of P saturation (Psat). A column study was conducted in which these soils were evaluated for soluble P concentration in runoff and leachate from two simulated irrigation events. There were strong correlations among all measures of soil P availability (r=0.66–0.90). Runoff soluble P was most strongly correlated with Pcc, Pae, and Pbc (r=0.98, 0.93, and 0.91, or 0.98, 0.90, and 0.85 in the first and second irrigation, respectively). The relationship of runoff soluble P to Pbc, Pae, and Pcc was characterized by a change point; runoff soluble P from soils <50 mg kg−1 Pbc was minimal, whereas at higher Pbc runoff P reached levels of environmental concern. Leachate soluble P was also correlated with Pcc, Pae, and Pbc (r=0.84–0.99). Across soils, leachate soluble P averaged 1.4 mg L−1, compared to 0.11 mg L−1 for runoff P. We conclude that Pcc, Pae, and Pbc are useful tests to rank the potential for P loss in irrigation runoff or drainage. Given the relative complexity of the Pae technique, Pbc and Pcc appear to be the most practical soil tests for this purpose.

Carbon Mineralization and Water-Extractable Organic Carbon and Nitrogen as Predictors of Soil Health and Nitrogen Mineralization Potential

Alternative techniques to evaluate soil potassium (K) availability for processing tomato production were compared to the standard ammonium acetate extraction procedure. Ammonium acetate exchangeable K (Kex), solution-phase K (Ksol), and K fixation potential (Kfp) were evaluated on soils from 40 California fields in which processing tomatoes were grown in 1996–98, and on soils from six K fertilization trials conducted in 1997–98. Ksol was determined in the supernatant of 1:10 mixtures (w/v) of soil and 0.01 M CaCl2, either extracted after an initial 30-minute shaking, or after 7 days of incubation at 25°C. Kfp was estimated by enriching dry soil with 1.0 cmol K kg−1 as aqueous KNO3, air-drying, then either extracting immediately with 1 M NH4Cl or after a 7-day incubation in 0.01 M CaCl2 solution. In all tomato fields, the determinate cultivars ‘Halley’ or ‘Heinz 8892’ were grown. Crop K status was evaluated at full bloom growth stage by K concentration in whole leaves, and at harvest by K concentration in fruit dry mass, total fruit K content (kg ha−1), and the incidence of yellow shoulder (YS, a fruit color disorder affected by soil K availability). Kex ranged from 0.17 to 1.33 cmol kg−1, leaf K from 18 to 43 g kg−1, and fruit K from 26 to 70 g kg−1. Ksol and Kfp were highly correlated with Kex (r=0.94 and 0.86, respectively). The Ksol and Kfp techniques utilizing K measurement after the initial shaking/extraction step were highly correlated with results from the procedures utilizing a 7-day incubation period (r=0.99 and 0.98 for Ksol and Kfp, respectively). Kex was more highly correlated with plant K status than either Ksol or Kfp, but correlations ranged from only −0.35 (for YS incidence) to 0.57 (for fruit K content). Potassium application reduced YS in 2 of 4 fertilization trials in which the disorder was prevalent, but none of the measures of soil K availability were predictive of either YS incidence, nor of fruit yield response to fertilization.

Nitrogen and Carbon Mineralization Dynamics of Manures and Composts

ABSTRACT The United States Department of Agriculture Natural Resources Conservation Service (NRCS) launched a national “Soil health initiative” in 2012; as a part of that effort, a soil health index (SHI) has been developed. The SHI is calculated using results of three soil tests: 24-h carbon mineralization following rewetting of air-dried soil (Cmin, by the “Solvita” proprietary method) and water-extractable organic carbon (C) and nitrogen (N). These tests are being promoted both as the inputs into the SHI calculation and as predictors of soil N mineralization potential. Soil was collected from 35 California fields in annual crop rotations; 20 fields were under certified organic management and the other 15 under conventional management, to provide a range of soil properties and management effects. Carbon mineralization was determined by the Solvita method, and by a comparison method utilizing head space carbon dioxide (CO2) monitoring by infrared gas analyzer (IRGA); additionally, two soil wetting protocols were compared, capillary wetting (the Solvita method) and wetting to 50% water-filled pore space (WFPS). Both water-extractable C (WEOC) and N (WEON) were determined using NRCS-recommended protocols. Net N mineralization (Nmin) was also determined after a 28-day aerobic incubation at 25°C. Solvita Cmin was highly correlated with the IRGA method using capillary wetting (R2 = 0.81). However, capillary soil wetting resulted in high gravimetric water content that significantly suppressed Cmin compared to the 50% WFPS method. Nmin was correlated with Solvita Cmin (r = 0.54) and with WEOC and WEON (r = 0.62 for each comparison); combining these three measurements into the SHI slightly improved the correlation with Nmin. The organically managed soils scored higher than the conventional soils on the SHI, with a minority of organic soils and the majority of conventional soils scoring below the NRCS target threshold. SHI and soil organic matter were correlated, suggesting an inherent bias that would complicate the application of a national SHI standard.