Study of Number of Nitrogen Fertigations on Improvement of Quantity and Quality of Thomson Navel Orange

To compare the effects of various nitrogen (N) fertigation frequencies on yield and fruit quality of Thomson navel orange, a field study was carried out in a randomized complete blocks design with five treatments and four replications during three years. Treatments included a subsoil N fertilizer placement (with drip irrigation) and four N fertigation frequencies (2, 4, 6 and 8 applications per growing season). Results of soil and leaf analysis were used to determine the annul amount of applied fertilizers. In subsoil placement treatment, urea was applied two times (second half of March and second half of May) and other fertilizers were applied only in March. In fertigation treatments, urea was applied by fertilizer tank in four frequencies, and other fertilizers were applied only in March. For all treatments, the amount and scheduling of irrigation was the same. The measured traits were total fruits weight (yield), single fruit weight, peel thickness, fruit diameter and length, acidity (TA) and total soluble solids (TSS) of the fruits. Analysis of the means showed that the yields of 6 and 8 fertigations were 5.6 to 32.1 percent more than the other treatments. But the yield of 8 applications per growing season differed significantly from 2 and 4 applications. Fruit weight and peel thickness of the treatments were not significantly different. Fruit diameter of 6-fertigation treatment was more than the other treatments, and had significant difference with 2-fertigation treatment. Significant difference between fruit juice quality of subsoil placement and fertigation treatments was not observed. But some differences were observed between fertigation treatments. In conclusion, for Thomson navel orange on the regions where similar to this research place, it can be suggested 6 applications of N fertigation.