Nitrogen fertilizers, application levels

Applications of Fertilizers for Control of Rice Diseases. In general, the application of fertilizers cannot be relied upon to solve all our major rice disease problems however, the application of properly balanced fertilizers reduces the severity of certain major diseases. Work on stem rot (Leptosphaeria salvinii Catt.) in Arkansas (3) and Japan (26) shows that the severity of stem rot can be reduced by increasing the potassium levels of soils in the problem areas. In Arkansas it has been shown that the application of nitrogenous fertilizer significantly increases stem rot severity, whereas the application of potassium fertilizer alone or in combination with nitrogenous fertilizers decreases stem rot severity. Consequently, in Arkansas the application of potassium fertilizer is widely practiced for stem rot control. 

Higher amounts can be found in certain varieties. In L. pimpinellifolum, levels as high as 40 mg per 100 g of fresh tissue have been reported, accounting for more than 95% of the total carotenoid content of these tomatoes (Porter and Lincoln, 1950). Nitrogen fertilizers and calcium sprays (0.2%) were reported to increase the lycopene content of tomatoes. Potassium deficiency may lower lycopene concentration however, very high potassium applications (>800 kg/ha) would cause a marked decrease in color uniformity disorders (Grolier, 2000). 

The soil macronutrients, nitrogen (N), phosphorus (P), and potassium (K), are essential for crop growth, and the use of commercial N, P, and K fertilizers has contributed greatly to the increased yield of agricultural crops. However, excessive fertilizer applications can lead to environmental contamination, primarily of surface and ground waters.Ideally, fertilizer application should be adjusted to match the requirements for optimum crop production at each within-held location, because there can be high spatial variability in the N, P, and K levels found within helds. ° ° ... 

Application of fertilizers is based on analysis of the soil (taking into account the vigour of the previous crop in the case of new plantings). Soil analyses, which provide information mainly about nitrogen levels, should be carried out at least once every 5 years. To guarantee comparability of the results, it is best to have the analysis always done by the same laboratory. 

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