Delivery methods
1. Preplant incorporation,
followed by additional fertilization based on crop growth stage
Tables 5 and 6 list recommendations for preplant fertilization followed by applications when fruit reach certain developmental stages. Preplant applications can be broadcast and disked in or side-dressed in bands 4" deep and 4" from the row at planting. The application can also be split between the two methods of incorporation.
2. Preplant incorporation, followed by fertigation
Typically, in the field, soils are tested to determine existing levels of the major plants nutrients. Fertilization is then based on soil test, e.g. Tables 5, 6, 7. This is followed by weekly fertilization through the drip irrigation system e.g. Tables 4, 8. Fertilization can be adjusted based on petiole sap levels to be determined on-farm (Table 2) or by tissue analysis (Table 3) which is determined by analytical laboratories.
3. Foliar sprays
Foliar sprays should be avoided because of the potential for damage to the foliage from spraying in hot or bright weather and because leaves do not absorb nutrients well. Under emergency conditions, however, foliar sprays are sometimes used while the situation in the rootzone is being corrected. Foliar sprays of urea dissolved in water at 2.5 g/L can be applied to correct a severe nitrogen deficiency. For phosphorus deficiency, foliar sprays with potassium or ammonium phosphate are possible, but are not recommended as they can cause serious leaf damage. For potassium deficiency, the crop may be sprayed with a solution of 20 g/L potassium sulfate. To correct calcium deficiency quickly, plants can be sprayed with a solution of 2-7 g/L calcium nitrate or a 0.3% calcium chloride solution. Such sprays are rarely beneficial in correcting BER, however, since calcium absorbed through the leaves cannot move into the fruit. Hence, only the Ca that lands on the fruit surface is utilized (Adams, 1999).
4. Organic methods
N requirements are harder to predict when working with organic materials. Organic materials tend to tie up nitrogen as they decompose and may require more nitrogen, at least early in the season, compared to inert materials. Later in the season, however, organic soils, substrates and compost additions release some of this N to the plant.