The efficiency and balance of nitrogen from one year's application was studied in a long-term fertigation experiment. Enriched nitrogen fertilizer, K~SNO3, was applied to a 22-year-old Shamouti orange tree with a history of high N applications (N3) and to an N-starved tree (N I ). The distribution of N in the different parts of the trees and in the soil was determined after the experimental trees were excavated.Similar total recovery of the labeled fertilizer N was found in the trees and soil in both treatments (N~ -61.7% N 3 -56%). However, the distribution between tree and soil was different. The amount of recovered residual fertilizer in the soil was much larger in the N 3 treatment than in N~.The highest percentage of fertilizer N was found in the new organs, i.e. fruits, twigs and leaves. The roots and branches took up only 6-14% from the labeled fertilizer.Only 20.9% of the leaf N and 23.4% of the fruit N in the N 3 tree originated in the labeled fertilizer, indicating translocation of N from older parts of the tree to new growth.Evidence was found of storage of N in the wooded branches, while the roots contained a surprisingly small part of labeled fertilizer.

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The suitability of sewage effluent for drip irrigation of cotton (Gossypium hirsutum) growing on a deep calcareous clay soil (Typic Chromoxererts) was studied during three seasons. Secondary effluent was compared with freshwater at three application rates, the average of which for the three seasons were: low (350 mm yr−1), standard (440 mm yr−1), and high (515 mm yr−1). Fertilizer was applied with the fresh water in order to deliver amounts of nutrients (average for the 3 years) equivalent to those in the effluent that contained 150, 180, and 230 kg N; 32, 37, and 46 kg P; and 80, 100, and 120 kg K ha−1 yr−1 for the three rates, respectively. In addition, the standard amount of fresh water was given with half the quantity of fertilizer, and without fertilizer.The concentration of available N and P in soil was increased greatly in all effluent and fertilizer‐amended freshwater treatments, while available K in the soil was increased to a lesser extent. In general, at equivalent application levels, no significant differences in the level of available N, P, and K in the soil or in their uptake by plants, were detected between effluent and fertilizer‐amended fresh water, although dry matter yield as well as N, P, and K accumulation were greater in the high‐application‐rate effluent treatment. The distribution of NO3‐N in the soil profile was controlled by drip irrigation and practically no build‐up of NO3− was detected below the 0‐ to 0.6‐m depth layer during the irrigation period (in summer). However, during the rainy, winter season, heavy losses of residual NO3‐N occurred, probably mainly through leaching.

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