Radiation absorption, growth and yield of pigeonpea cultivars as influenced by sowing dates

Two pigeonpea (Cajanus cajan) cultivars GT-100 (determinate type) and BDN-2 (indeterminate type) were planted on three sowing dates (30 June, 20 July and 9 August) in 1993 and 1994. Pigeonpea sown on the earliest date attaine d the highest leaf area index (LAI), absorbed the largest amount of photosy nthetically active radiation (PAR) and produced the highest total dry matte r (DM). The differences in biomass and seed yield among sowing dates were l argely ascribed to totals of PAR absorbed and dry matter produced, especial ly in the reproductive phase. The high LAI persistence and PAR interception , coinciding with the podding phase, appeared to be mainly responsible for the increased yield in early sowings. Radiation use efficiency decreased as sowing was delayed, but did not have much effect on DM accumulation in var ious phases nor on final yields. Although the extinction coefficient was no t influenced by sowing dates, it was inversely related to leaf area index i n both cultivars. Between the cultivars, the differences in biomass reflect ed the differences in PAR absorbed and DM accumulation, depending upon leaf area development and growth duration. The cultivar GT-100 had a higher see d yield and harvest index than BDN-2 due to more of the DM produced being p artitioned into pods during the reproductive phase on account of its determ inate growth habit. Early sowings of determinate cultivars could maximize b oth vegetative and reproductive growth, capture more light and produce more seed yields under rainfed conditions.