Early maturing cotton genotypes for enhancing the productivity of cotton - wheat system: a physiological analysis

Physiological analysis of cotton-wheat system with 20 cotton and 6 wheat genotypes was done in relation to the cropping system productivity. The duration of different cotton genotypes showed large variation and ranged from as early as 130 days to late up to 185 days. Genotypic variations in cotton genotypes for different morphological (shoot length, number of monopods and sympods), physiological (LAI and biomass) and yield (boll number and boll weight) parameters were significant. Higher vegetative growth (i.e. LAI) at 90 DAS and biomass (175–273 g plant ⁻¹) at 120 DAS was observed mostly in early genotypes as compared to late genotypes. Many early maturing genotypes also possessed significantly higher number of sympodial branches (33–37 plant⁻¹) and significantly higher seed cotton yield (1.93 to 2.34 t ha⁻¹) than the late types (1.81 to 2.04 t ha⁻¹). Variety CNH-36, CNH-120, RS 810, Pusa 8–6, RS2013, Vikas, LH-1556, Surbhi and hybrids Ankur 651, Omshanker and LHH-144 appeared physiologically more efficient in terms of photosynthesis (Pn) and photosynthetic water use efficiency (PWUE). In wheat, LAI at 120 DAS and biomass at maturity were significantly reduced in late sown wheat. The grain yield of six wheat genotypes after cotton ranged from 4.7 to 5.2 t ha⁻¹ and was significantly higher in wheat genotypes UP 2338, HD 2687 and PBW 343. Late sowing of wheat due to late harvesting of cotton significantly reduced the wheat yield in all the genotypes. Photosynthesis, transpiration and photosynthetic radiation use efficiency were higher in timely sown wheat genotypes, however photosynthetic water use efficiency was less. Yield of cotton-wheat system in terms of wheat equivalent yield (WEY) and net returns (NR) of cotton-wheat system were also reduced with the late sowing of wheat (8.4 and 6.2%, respectively). Highest WEY (11.1–11.8 t h⁻¹) and NR (45.5–51.3x1000 Rs. ha⁻¹) of cotton-wheat system were observed with early maturing cotton genotypes (LRA-5166, LH 1556, Ankur-651, CNH-120, F-1861 and Omshankar) followed by UP2338, HD2687 and PBW343 (wheat). These findings reveal that early maturing genotypes of cotton along with normal sowing of wheat crop can improve the productivity and NR of cotton–wheat system.