Title : Applying nitrogen to citrus
Visit Count : 3377 Time(s)
Upload Date : 7/31/2016 - 6 Year(s) ago
Category : citrus
Sunday, July 31, 2016
Visit Count : 3377 Time(s)
Upload Date : 7/31/2016 - 6 Year(s) ago
Category : citrus
Functions of nitrogen
Nitrogen is the element that has the greatest effect on citrus production, and citrus needs more nitrogen than any other nutrient. Nitrogen is a component of chlorophyll (the green pigment in leaves), and is associated with important tree functions such as growth, leaf production, flower initiation, fruit set, and fruit development and quality.
Shortage of nitrogen
A nitrogen shortage causes the loss of green colour from the leaves, resulting in an even paleness. A deficiency of nitrogen in the spring makes the leaves pale and small. Old leaves shed early in the season, causing the foliage cover to become thin, and twigs to die back. Tree growth is retarded, and cropping suffers through poor fruit set and smaller fruit.
Excess nitrogen
Too much nitrogen lowers fruit quality and shortens storage life. The fruit is large and puffy, maturity is delayed, and regreening increases. The skin thickens and becomes coarse, while the percentage and quality of the juice decline. The colour takes longer to break in oranges, and in navels rind staining increases. The adverse effects of high nitrogen are worse when phosphorus is low. Excess nitrogen promotes lush tree growth and late flushes which are susceptible to frost.
Nitrogen fertilisers
Nitrogen fertilisers include ammonium nitrate, urea, ammonium sulphate, ammonium phosphates, and compound or mixed NPK (nitrogen, phosphorus, potassium) fertilisers. The nutrient percentages in common citrus fertilisers and manures are given in. District fertiliser rates are given in. The form of the nitrogen in the fertiliser affects its performance and determines the suitability of a fertiliser for a particular situation. However, the cost per kilogram of nitrogen is usually the deciding factor as to which fertiliser is chosen. The nitrate in ammonium nitrate moves quickly and easily to the roots, but it can be lost through leaching by heavy rain. Ammonium fertilisers, such as ammonium sulphate, are less liable to leaching, but they tend to make the soil very acidic after years of regular use. Per unit of nitrogen, ammonium nitrate is only one-third as acidic as ammonium sulphate. Urea is a cheap and concentrated nitrogenous fertiliser. Cultivate or water it into the soil to prevent it from volatilising as ammonia. Urea used as a foliar spray is absorbed into the leaves in a few hours; but the amount of nitrogen applied in a single spray is small (less than 10 kg N/ha). Foliar-applied urea is therefore used to supplement, rather than replace, normal applications of fertiliser to the soil. This can give an extra boost when needed (for example, when a heavier crop than expected has been set). Urea used for spraying should have a low biuret content (less than 0.4%), as higher levels cause leaf burn. Biuret is not a problem when urea is applied to the ground. Spring and early summer are the best times to apply nitrogen to citrus. Research has shown that the demand for nitrogen in citrus is highest from bloom through June and most of the supplemental nitrogen fertilizer should be applied during this time period.

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