The possible mechanism of cotton premature senescence under drip irrigation below mulch film—from the perspective of growth and nutrient

The premature senescence of cotton under drip irrigation below mulch film (DI) is much more widespread than under flooding irrigation (FI), and the change of plants nutrient under DI has been regarded as a possible influencing factor. In this study, a field experiment was conducted to investigate the cotton growth and nutrient status under DI in comparison to FI. The results indicate that there are severe symptoms of premature senescence at the later growth stages of cotton under DI, while there are not the symptoms under FI. At 125 DAS (late boll), the shoot biomass under DI is significantly higher than that under FI, while root biomasses show the opposite trend, and the shoot/root ratio under DI is significantly higher than that under FI. The shoot dry weight of plants grown under DI is abruptly decreased from 125 DAS (late boll) to 160 DAS (harvest). Field observations indicate the main reason for the decrease is the shedding of a large number of leaves, squares and bolls. The shoot to root ratio under DI is also decreased to the same level as that of the FI treatment. To analysis the cotton leaf nutrition, it would be found that the nitrogen and phosphorus concentrations of old leaves are lower than those of young leaves under both of DI and FI at the later growth stages, whereas the potassium concentration is opposite. The K concentration of young leaves under DI is lower than that under FI, and the K concentration of cotton shoot also shows a same trend. These results indicate that the premature senescence of cotton under DI may be that the K need of the shoots exceeds that K amount of the roots is able to supply.