OPTIMIZING OF NITROGEN FERTILIZATION UNDER DRIP IRRIGATION SYSTEM IN SANDY SOIL USING NUCLEAR TECHNIQUES

Abstract

A field experiment was conducted on sandy soil at the Experimental Farm of Soils and Water Research Department, Nuclear Research Center, Atomic Energy Authority, Cairo, Egypt. This experiment aimed to explore the impact of certain scenario dealt with irrigation scheduling (water regime) and nitrogen fertilization strategy on pea crop production with special emphasis on nitrogen fertilizer use efficiency and water use efficiency and productivity. The experiment was carried out during the summer, 2013 under drip irrigation system using seeds of Pea (Pisum sativum) cv. Kafr Elsheikh 1 as a tested crop. Two water regimes representing W1 (100% ETc) and W2 (75% ETc) were applied. Nitrogen fertilizers were applied in two forms, i.e. urea and ammonium sulfate with 100% and 75% rates from the recommended rate required for pea fertilization. Unfertilized control was also included. Nitrogen fertilizer rates were splitted into three doses distributed along three months of plant growth as 15%, 15% and 10%, respectively at one month in between. 15N labeled ammonium sulphate (15NH4)2SO4, "20.6 % nitrogen" and urea (15NH2) CO (46%) with enrichment of 2% 15N a.e. was used. The isotope dilution concept was applied to distinguish between the different N sources gained or derived to different parts of pea plants. This technique gave us the chance to estimate %NUE accurately. Experimental treatments were replicated three times and distributed in complete randomized block design (CRBD). This work aimed at achievement of the proper water requirement scheduling and the best form and rate of nitrogen fertilizer resulted in the remarkable yield of pea crop grown on sand soil under surface drip irrigation system. To achieve this aim, neutron scattering technique and 15N stable isotope technique were applied. The obtained results could be summarized as following: • Neutron Calibration Curves 1- Twenty neutron calibration curves of the five sites (0, 12.5 and 25 cm between drippers and also between lateral lines) were done. The obtained data pointed to soil water distribution and values of total hydraulic potential depend on soil moisture contents using calibration curves, so single calibration for the soil depths will not be accurate then wrong data and the predicted potentials will be false. 2- Neutron calibration curves at 30 and 45 cm depth were identical curves for the all five sites while they were at 60 and 75 cm depths. 3- The soil moisture content measured in the soil just after and before the next irrigation using neutron scattering meter at regular intervals through growing season. 4- Therefore, data inserted into the Russian SAD program (including equation of the relationship among the ETa and the deficit in the relative humidity, meteorological data needs of the studied area for ten years) was used to form a perfect system of irrigation with another form of the crop coefficient kc along the growing season. Output data of the program pointed out the provision of 24% of the irrigation water requirements under both treatments of W1 and W2 regimes. • Water Scheduling 1- Application of 75% ETc treatment saved about 25% of irrigation water requirements as compared to 100% ETc treatment, so, it could be considered the proper water regime that acheived considerable yield. • Yield Parameters and nitrogen uptake 1- Root dry weight was higher in case of W1 than W2 regime. 2- Both urea and ammonium sulfate applied at 100% rate achieved higher root dry weight than those induced by 75% of nitrogen application rate. 3- There was no significant difference between the two nitrogen forms when root dry weight was considered. 4- Shoot dry weight has the same trend. 5- Seed yield was a little bit differing, but insignificant, in case of W1 regime as compared to W2 regime.