Optimizing the uniformity of irrigation and fertilization

Abstract

Using a second-degree equation to approximate the relationship ‘water available to the plants-yield’, a coefficient of non-uniformity ( F nun) has been derived which is proportional to the yield loss caused by the non-uniformity of irrigation. Using the criterion of the minimum costs and losses, the optimum coefficients of non-uniformity in furrow and sprinkler irrigation have been determined. On this basis, in the case of furrow irrigation, the values of some practically usable indices, such as ‘relative extension of irrigation time’ and ‘required number of streams which must reach the downstream end of furrows’ have been determined. Achieving these values in the field will guarantee an optimum irrigation uniformity. In sprinkler irrigation, under the specific economic conditions in Bulgaria, the optimum spacing of sprinklers (a given type of sprinkler head) has been determined for different wind velocities and for two different groups of crops. Under conditions of water shortage, when crops are irrigated only during some selected growth stages, the relationship ‘evapotranspiration-yield’ is multi-valued. Under these conditions, a considerably higher yield is obtained when water is applied during the most sensitive stages of growth. In that case, the uniformity of irrigation must be as high as possible. When nitrogen fertilizer is broadcast over the soil surface, the loss of yield and the required optimum distance between the runs of the broadcasting implement can be determined, using the coefficient of non-uniformity, F nun.