Potassium to nitrogen ratio favors photosynthesis in late-planted cotton at high planting density

Late sowing of short growing season cotton, planted in high density with one time fertilization is a potential economic alternative for the conventional cotton growing practice in the Yangtze River Valley, China. The appropriate proportion of nutrients is indispensable for an economic crop production. Therefore, the present study was designed to explore the best relative ratios of potassium (K) to nitrogen (N), under a new short-season and high density planting model, based on the photosynthetic performance of cotton plants in relation with the yield. A two-year (2016–17) field experiment was conducted with three K relative ratios to N [0.8 (K08: 168 kg ha−1 K2O), 1.0 (K10: 210 kg ha−1 K2O) and 1.2 (K12: 252 kg ha−1 K2O)]. The results indicated that K10 increased seed cotton and lint yield by 10–20% and 10–24%, respectively, over K08 and no difference was existed between K10 and K12. Similarly, K10 and K12 increased SPAD value by 3–10% and 11–18%, photosynthetic rate by 7–57% and 0.7–89%, and chlorophyll fluorescence parameters by 1–8% and 1–29%, respectively, as compared to K08. And the highest photosynthetic attributes were achieved for the 4th main stem leaf from the top at peak bloom (PB) stage. These results suggested that the K10 is the most suitable ratio as for cotton yield and economic concerns under the newly proposed planting model in the Yangtze River Valley, China.