Nitrogen and carbon mineralization rates of 19 manure and compost samples were determined in 1996, with an additional 12 samples evaluated in 1997. These organic amendments were mixed with a soil: sand blend at 2% by dry weight and the amended blends were incubated at constant moisture for 12 (1996) or 24 weeks (1997) at 25 °C. Net N mineralization was measured at 4- (1996) or 8-week (1997) intervals, C mineralization at 4-week intervals in 1997. Pots of the amended blends were also seeded with fescue (Festuca arundinacea Shreb.) and watered, but not fertilized, for 17 (1996) or 18 weeks (1997); N phytoavailability was estimated from fescue biomass N and mineral N in pot leachate. An average of 16%, 7%, and 1% of organic N was mineralized in 12 weeks of incubation in 1996, and an average of 15%, 6%, and 2% in 24 weeks of incubation in 1997, in manure, manure compost, and plant residue compost, respectively. Overall, N recovery in the fescue assay averaged 11%, 6%, and 2% of total amendment N for manure, manure compost, and plant residue compost, respectively. Mineralization of manure C averaged 35% of initial C content in 24 weeks, while compost C mineralization averaged only 14%. Within 4 (compost) or 16 weeks (manure), the rate of mineralization of amendment C had declined to a level similar to that of the soil organic C.

Windrows of municipal yard and landscape waste at three commercial composting sites in California were sampled at ≈3-week intervals through 12 to 15 weeks of composting to observe changes in physiochemical and biological characteristics of importance to horticulture. Initial C, N, P, and K content averaged 30%, 1.3%, 0.20%, and 0.9%, respectively. Carbon concentration declined rapidly through the first 6 to 9 weeks, while N, P, and K remained relatively stable throughout the sampling period. Few viable weed seeds were found in any compost. A high level of phytotoxicity, as measured by a tomato (Lycopersicon esculentum Mill.) seed bioassay, was observed at only one site; overall, the degree of phytotoxicity declined with compost age. Short-term net N immobilization (in a 2-week aerobic incubation) was observed in nearly all samples, with an overall trend toward decreased immobilization with increased compost age. In a 16-week pot study in which fescue (Festuca arundinacea Shreb.) was grown in compost-amended soil, net N mineralization averaged only 2% to 3% of compost total N content. Neither composting site nor duration of composting significantly affected either N mineralization rate or fescue growth. Growth of vinca (Catharanthus roseus Don.) in a blend of 1 compost : 1 perlite increased with increasing compost age. Overall, at least 9 to 12 weeks of composting were required to minimize the undesirable characteristics of immature compost.

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 (K ex ), solution-phase K (K sol ), and K fixation potential (K fp ) 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. K sol was determined in the supernatant of 1:10 mixtures (w/v) of soil and 0.01 M CaCl 2 , either extracted after an initial 30-minute shaking, or after 7 days of incubation at 258C. K fp was estimated by enriching dry soil with 1.0 cmol K kg 21 as aqueous KNO 3 , airdrying, then either extracting immediately with 1 M NH 4 Cl or 1389

The effect of transplant production and handling practices on processing tomato growth, yield, and fruit quality were evaluated in five field trials in California. In 1999, processing tomato (Lycopersicon esculentum Mill. cv. Halley) transplants were obtained from a number of commercial transplant producers and taken to the Univ. of California-Davis (UCD) where treatments were imposed for 1 week prior to transplanting. Treatments included N and P fertilization, exposure to lath house or greenhouse temperature, withholding water, and storage in the dark for 2 days to simulate shipment from greenhouse to field. Nine treatments per site were compared in field trials at Yolo, Woodland, and Knights Landing. In 2000, transplants were grown at UCD under varying nutrient regimes, including P fertilization rates ranging from weekly application of 0 to 90 mg·L -1 . Two commercial field trials comparing 8 treatments were conducted near Winters and Newman. Although transplant production and handling practices significantly influenced relative growth rate in the 3-4 weeks following transplanting in all 1999 trials, effects on fruit yield were minimal, with only one treatment at Woodland showing significantly lower yield and no treatment differences in crop maturity, fruit soluble solids, or juice color observed at any site. In 2000, plants receiving no weekly P fertilization showed slower growth in the 3 weeks after transplanting, but no treatment differences were observed after 6 weeks. Fruit yield, soluble solids content (°Brix) and juice color were unaffected by transplant treatment. We conclude that transplant production and handling practices tested had minimal differential effect on the subsequent field performance of processing tomato transplants in the Central Valley of California.

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