Determination of irrigation water and fertilizer phosphorus requirements of wheat in Bangladesh using tracer techniques

The optimum quantity and frequency of application of irrigation water and the response of wheat to different levels of phosphate fertilizer were studied, using 32P-labelled triple superphosphate. A split-plot design with irrigation treatments in the main plots and phosphorus treatments in the sub-plots was used, with two levels of phosphate application (60 and 120 kg P2O5/ha, plus control). The six water treatments consisted of six combinations of 1, 2 or 3 irrigations to 1 X or 2 X field capacity of the upper 45 cm of soil, with 'no irrigation' as control. The moisture content of the soil profile of each plot was monitored with a neutron moisture meter, and the amounts of water required at each irrigation were calculated. Plant samples were harvested at mature grain stages. The mean grain and straw yields of wheat were 4.43 and 4.15 t/ha, respectively. The effects of irrigation intensity and frequency were insignificant. The percentage of fertilizer derived P in wheat plants varied between 57.83 and 72.88, depending on irrigation treatment. Single applications of water to 1 X field capacity or 2 X field capacity at the grain filling stage resulted in the highest uptake of fertilizer P. The application of superphosphate at 60 and 120 kg P2O5/ha increased the grain yield and straw yield significantly. But the yield of wheat from the 60 and 120 kg P2O5/ha treatments did not differ significantly from each other. The contribution of fertilizer P to the total plant P was higher from 120 kg P2O5/ha than that from 60 kg P2O5/ha, being 71.5% and 60.3%, respectively