Sign up for email alerts of new Fluid Journal issues!
Fluid Journal : Fluid Journal 1996-1998
Winter 1996 flexibility, allowing for daily N application if desired. The question of fertigation frequency has not been extensively re- searched, but most available information suggests that weekly additions are as effective as more frequent applications. Crop N status. Conventional plant tissue analysis, in which tissue is dried, ground and chemically analyzed in a laboratory, is the most accurate way to determine crop N status. Through decades of experience, N sufficiency guidelines have been developed for most vegetable crops. Although not specifically developed for drip irrigation, these standards are still generally appli- cable. To get the most useful data, particu- lar attention should be given to: 1) plant sampling technique, 2) determination of growth stage, and 3) handling and prepara- tion of samples. Fertility planning Developing an efficient fertility plan involves three additional factors to be considered. Estimating soil N. Residual ammonium and nitrate present in the soil should be esti- mated at the start of the season through preplant sampling. Estimate of how much N will be mineralized as the season progresses is difficult. Crop development rate. Relative crop development rate (directly tied to tempera- ture) should be accounted for so fertilizer additions can be planned on the basis of daily and weekly needs. Total crop N needs are relatively independent of environmental conditions. Water N content. Nitrogen content of irrigation water should be determined where substantial amounts of nitrate (especially in well water) may be present. Some wells in the Salinas Valley and the eastern San Joaquin Valley contain more than 10 ppm. Formula for determining N content is: ppm of NO3_N in water x 0.23 = pounds N per acre inch. For example, 18 inches of water with an NO3_N content of 10 ppm would add 41.4 lbs/A of N over the cropping season. Table 1 lists typical fertigation programs for some major vegetable crops. It should be used only as a guide, to be modified as individual circumstances require. Dr. Hartz is extension vegetable specialist at the University of California, Davis. Work sponsored by Fertilizer Research and Education Program, California Depart- ment of Food and Agriculture. ! Table 1. Nitrogen fertigation requirements of vegetable crops under California conditions. Crop Growth State Approx N requirement Lbs/A/Week Broccoli Early growth 5 15* Mid season 10 20 Button formation 15 30 Head development 10 20 Lettuce Early growth 5 10 Cupping 10 20 Head filling 15 30 Pepper Vegetative growth 5 10 Early flowering/fruit set 15 30 Fruit bulking 15 20 First harvest 5 10 Tomato Vegetative growth 5 10 Early flowering/fruit set 15 20 Fruit bulking 10 15 First harvest 5 10 Cucumber Vegetative growth 5 10 Early flowering/fruit set 10 20 Fruit bulking 10 15 First harvest 5 10 *Higher values represent fertigation needs in low residual N soils and/or under high temperature (rapid growth) conditions.
Fluid Journal 1993-1995
Fluid Journal 1999-2001