Interactive effect of nitrogen fertilizer and plant density on photosynthetic and agronomical traits of cotton at different growth stages

Individual effects of application of nitrogen (N) and plant densities (PD) were reported in various studies; however an interactive effect of N and PD in cotton was not studied. To explore the benefits of interactive effects of N fertilizer and PD to increase the quality of cotton. This study was carried out in randomized complete block design (RCBD) with split plot arrangement. In split plot arrangement, main plot was consisted of N application rate and in sub plots different PD were done. There were two nitrogen levels; low N level (F1) 120 kg ha⁻¹ and high N level (F2) 180 kg ha⁻¹ and three planting densities; 8 plants m⁻² as low density (LD), 10 plants m⁻² as medium density (MD) and 12 plants m⁻² as high density (HD). In this study we observed the interactive effect of N application levels and PD on cotton photosynthetic and agronomic traits of various stages of development. Results showed that cotton growth and N contents was varied among treatments on different development stages. Plant biomass production, photosynthetic rate (Pn), intercellular CO₂ (C_i), water use efficiency (WUE) and N contents were unaffected at the seedling stage by N application rate and PD, however, the highest Pn, C_i and N contents was at squaring stage followed by blooming stage. Higher seed cotton yield and lint yield were obtained F1 with HD, and F2 with MD yielded the highest N contents and cotton yield among treatments. We found that the squaring stage was more critical, followed by the blooming stage when considering N rate and PD.