Abstract:
Continuous rice-wheat cropping systems that are heavily dependent on irrigation water, has become a matter of great concern in South Asian countries, particularly in India. This has lead to nutrient and ground water depletion, as well as soil degradation due to formation of saline/sodic soils. Due to this, a field experiment was conducted on a sandy loam soil in New Delhi, to determine nutrient content and uptake by a late-sown-wheat (HD 2285) under varying water, nitrogen and zinc levels. Treatments comprised of four levels of irrigation in main plots and a combination of three N and two Zn levels in the sub plots of a split plot design, replicated thrice. Nitrogen content in the above ground biomass declined with progression in wheat growth, from a maximum of 4.0% at 30 days after sowing (DAS) to a minimum of 1.1% at 90 DAS. This was however inversely associated with an increase in N uptake from a minimum of 12.4 kg/ha to a maximum of 99 kg/ha over the same period. Nitrogen content in biomass at 90 DAS, increased significantly (P≤0.05) with increase in irrigation levels, attaining a maximum of 1.393%, under the two irrigation treatment (I2), applied at crown root initiation and flowering stages of wheat. Highest grain N (1.7%) was obtained with I2 and I3 (four irrigation, given at CRI, jointing, flowering and milk stages) treatments. N uptake ranged from 54.7 to 115.8 kg/ha N under the (I0) and (I3) treatments, respectively. Application of 100 kg/ha N significantly increased N uptake in the aboveground biomass at the 60 and 90 DAS growth stages. Grain N consisted of 63 to 69% of total N uptake in wheat. Application of I3 resulted in the highest straw Zn content (44.3 and 40.7 mg/ha) and zinc uptake (177.6 and 159.4 g/ha) was with I3 in seasons I and II, respectively. Zinc application at the rate of 5 kg/ha significantly increased zinc uptake in the grains (82.04 and 72.51 g/ha) over the no zinc application treatment (76.03 and 66.50 g/ha) in both seasons, respectively. Where input and water are limiting (e.g. ≤ 48 kg/ha N and 186 mm water), mean grain yields of 2.29 tons/ha can be obtained. When water and N are adequate (i.e. 110 kg/ha N and 250–330 mm water irrigated 2 to 4 times), 3.96 tons/ha of wheat grain can be harvested.
