Production guide: Nitrogen and water management for coastal cool-season vegetables.
G.S. Pettygrove, S.R. Grattan, B.R. Hanson, T.K. Hartz, L.E. Jackson, T.R. Lockhart, K.F. Schulbach and R. Smith.
Publication 21581, University of California, Division of Agriculture and Natural Resources, Oakland, CA. 1998.
The main cool-season vegetables grown in California are lettuce, broccoli, celery, cauliflower, and cabbage. The farm-gate value of these crops was$2.2 billion in 1995 (about 10 percent of the total value of agricultural commodities in the state). There is some fall and winter vegetable production in the San Joaquin or Imperial Valleys, but the majority of cool season vegetable production takes place in the central and southern coastal areas, with over $1 billion coming from Monterey County alone. Other important production areas are found in Santa Barbara, San Luis Obispo, Ventura, Santa Cruz, and San Benito counties.
The high level of productivity in these areas depends on a number of factors, but two of the most critical are nitrogen and water. Unfortunately, the shallow root systems of cool-season vegetables means that applied water and nitrogen are not used very efficiently: harvest removals of nitrogen are typically only half of the amount of nitrogen applied as fertilizer, for example. The result over the last several decades has been an increase in nitrate levels in the groundwater under these agricultural lands. This poses a significant problem as many municipal water supplies draw from this groundwater. This handbook provides important information about ways of managing water and nitrogen more efficiently in order to reduce the problem of groundwater contamination.
The first section of the book presents a concise and clear discussion of the nitrogen cycle and how farming practices influence the various processes and components of that cycle. The authors provide detail on the relative amounts of the various forms of nitrogen in the soil, and the factors that affect the transformation of nitrogen from one form into another, as well as its availability for crop uptake. Other topics include nitrogen additions to the soil plant system, plant uptake and harvest removal, and nitrogen loss pathways.
The heart of the guide is the chapter on management measures and recommended practices for improving nitrogen use efficiency. For the purposes of this book a management measure is defined as the best economically achievable technology or process for limiting movement of nitrogen into ground or surface waters, while a recommended practice is a specific farming technique for accomplishing the management measure.
The measures and practices described in the guide were developed by a team of growers, fertilizer retailers, crop consultants and University of California researchers. The authors state in the introduction to the book that, although there was not always consensus, the group was in most cases able to agree on practical and economically feasible practices. The resulting recommendations included in the guide have been scientifically validated under Central Coast conditions. The authors are careful to label the practices "recommended" (not "best") management practices since no single management technique will work well in all situations. A summary of the nine management measures and the recommended practices under them is included in Table 1 (p.12). Each of these is described in more detail in the guide.
The production guide is supplemented with numerous tables and figures and several excellent appendices on soil and plant tissue testing, cover crops, manure management, and other practices that alter crop nitrogen use efficiency.
Production Guide: Nitrogen and Water Management for Coastal Cool-Season Vegetables is available from DANR Communications Services at (800) 994-8849 or (510) 642-2431. The cost is $10.
For more information: G.S. Pettygrove, Dept. of Land, Air and Water Resources, University of California, Davis, CA; Email: gspettygrove@ucdavis.edu
DEC.597 Contributed by David Chaney
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