Studies on Water Use Efficiency of Crops and Ion Movement. Part of a Coordinated Programme on Agricultural Nitrogen Residues with Particular Reference to Their Conservation as Fertilizers and Behaviour as Potential Pollutants. Fin

摘要

Apparent recovery of N by wheat Pak-70 from urea applied at the rate of 120 kg N/ha under normal irrigation practices (3-4 irrigations during the growing season) was up to 35%. The proportion of nitrogen derived by wheat from the applied fertilizer was low (5-16%), showing that most of the N taken up by wheat came from sources other than fertilizer, mainly from the soil itself. This is evidenced by the high A values and by the higher inorganic N-content after wheat harvest. The total nitrogen content of surface layers generally increased at the end of each growing season but the total N-content decreased as a function of time. Up to 2.5% of total N in the surface layers originated from the applied fertilizer. Some movement or local mineralization appears to have occurred at lower depths but the N may be left largely as residue in soil. Surface management of N-residues which are susceptible to losses is therefore important. Marked changes were observed in the water content of top layers of the soil profiles, following each wheat irrigation. The water content was more or less uniform below a depth of 75 cm. (Atomindex citation 12:626953)