Effects of irrigation and nitrogen fertilization on photosynthesis, leaf area index and dry matter production of wheat on a clay terrace soil of Bangladesh

A field research was conducted at the university farm of Bangabandhu Sheikh Mujibur Rahman Agricultural University, Bangladesh, during November 1997 to March 1998 in order to study the effects of irrigation and nitrogen fertilization on the leaf photosynthesis, leaf area index and dry matter production of wheat. The experiment was executed in the split-plot design comprising the combination of the five levels of irrigation arranged as a main plot and the four rates of N application distributed to a sub-plot. The five irrigation treatments were: I sub0 -no irrigation after the establishment of seedlings; I sub1 -one irrigation at 23 days after sowing (DAS) of wheat seeds; I sub2 -two irrigations: one at 23DAS and the other at 60DAS; I sub3 -two irrigations: one at 23DAS and the other at 80DAS; I sub4 -three irrigations: at 23, 60 and 80DAS. The four rates of N application were: N sub0 -no application of N fertilizer; N sub1 ( N sub2 and N sub3 -application of N at the rates of 80, 120 and 160kg ha sup(-1), respectively. Both irrigation and N application have created a significant impact on leaf photosynthesis (LPn), leaf area index (LAI), crop growth rate (CGR) and biomass production of wheat. Irrigation scheduling which included irrigation at the grain filling stage (80DAS) coupled with N application up to 120kg ha sup(-1) significantly increased LPn, LAI, CGR and biomass production. With respect to the growth stage, LPn and CGR were highest at the anthesis stage (70-75DAS) and LAI was maximum at the booting stage (60DAS). Increased dry matter accumulation at maturation was mainly due to the increased weight of grains.