Enhancing cotton sustainability: Multi-factorial intercropping, irrigation, and weed effects on productivity, quality and physiology

Drought stress and weed infestation are significant factors that significantly decrease cotton yield. Increasing the variety of plants within a cotton field ecosystem can strengthen its stability and protect it from susceptibility to both biotic and abiotic pressures. In this two-year experiment (2021 and 2022), the effects of intercropping systems (four growth conditions including mono- and inter-cropped cotton varieties Golestan and Hekmat with Nepeta crispa and dragon's head (Lallemantia iberica)), irrigation (three intervals of 3, 6, and 9 days), and weed competition (weed-free and weedy plots) on the agronomic performance, physiological characteristics, and seed quality of cotton in a semi-arid region of Iran were studied. In 2021, the volume of irrigation water applied was 9873, 6100, and 4650 m3 ha−1 for irrigation intervals of 3, 6, and 9 days, respectively. In 2022, the volumes were 9071, 5605, and 4272 m3 ha−1 for the corresponding irrigation intervals. Over two years, Xanthium strumarium, Amaranthus retroflexus, and Portulaca oleracea were the dominant weed species. Weeds had the most significant impact on total dry weight; weed control increased plant vigor and growth, ranging from 1.4 to 2.3 times, while weed impact on cottonseed yield ranged from 18% to 96% reduction. Increasing irrigation intervals resulted in reductions in various parameters, with decreases of 39%–80% in total dry weight, 34%–57% in cottonseed yield, and 48%–72% in lint yield. The harvest indices for seed cotton, cottonseed, and lint ranged from 35.3% to 56.5%, 18.3%–35.0%, and 15.4%–20.5%, respectively. Weeds were responsible for a 17% decrease in the 1000-seed weight. As the irrigation intervals increased from 3 days to 6 days and 9 days, the number of bolls per plant decreased by 19%–85%. Extending the irrigation interval from 3 days to 6 days and 9 days resulted in a substantial decrease in the photosynthetic rate, ranging from 42% to 92%. Mono-cropped Golestan performed well under unstressed conditions such as 3-day interval irrigation and weed-free conditions. On the other hand, intercropped Hekmat demonstrated better resilience to both moisture and weed stresses. The LER (Land equivalent ratio) indices of both intercropping systems were generally favorable, indicating higher productivity compared to sole cropping. The intercropping systems consistently showed the highest LER indices under weedy conditions, highlighting the significance of intercropping as a valuable method in integrated weed management.