Influence of Mulched Drip-Irrigation with Brackish Water on Element Composition of Soil, Cotton, and Cotton Yield

Irrigation with brackish water has a long history throughout the world. Irrational use of brackish or saline waters, however, may lead to soil salinization and reduction of crop yields. In order to promote reasonable applications of brackish water and fertilizer irrigation, a series of experiments of mulched drip-irrigation with brackish and fresh waters were carried out at Bazhou Irrigation Experimental Station (Korla, Xinjiang, China). Plant and soil samples were collected at every growth stage. Cotton yields were measured at boll opening stage. Nine elements (Ca, Na, Mg, K, Cu, Fe, Mn, Zn and B) of each sample were tested in triplicate by ICP-OES (ICAP6300) after pretreated. The influence of water quality on the element compositions of soil and cotton and cotton yield were discussed based on the experiment. The results show that growth rate of Na⁺ in narrow rows and interspace of mulches was lower than that in wide rows because of higher content of Cu, Fe, Zn. The ratios of K⁺/Na⁺ and Ca²⁺/Na⁺, however, in most cotton organs show no significant differences between the two treatments. From buds to boll stages, brackish water irrigation enhanced the accumulation of above ground dry matters, which was favorable for vegetative development. From boll to boll opening stages, root and reproductive growth under brackish water were superior to that for fresh water. Furthermore, dry matters, boll weight, numbers of boll per unit area and cotton yield under brackish water were higher than those for fresh water. According to the correlations analyses, relationship between most trace and macro elements was weak. High correlations, however, were found among manganese, boron, and calcium. Within a certain threshold, boron, manganese promoted the absorption of calcium in cotton. It has been proved that a rational use of brackish water will not lead to the growth stress. On the contrary, it would not only lower the growth rate of Na⁺ in the soil effectively, but also strengthen cotton's resistibility to salt stress and increase cotton yields as well.