Spatial-temporal Evolution Of Solutes In Water-soil-cotton Ecosystem Under Mulched Drip Irrigation With Brackish Water And Its Application In An Arid Region

In arid areas, brackish water is commonly used for irrigation because of water shortage and soil nutrient deficiency. However, irrational irrigation with brackish water may lead to the accumulation of saline ions such as sodium, which might inhibit plant growth or even crop failure. For exploring the reasonable utilization of brackish water from the aspect of soil solute environment, methods as cotton-field experiment with different alternative irrigation, pot experiment, indoor tests analysis and numerical modeling were conducted from 2012 to 2014. The main conclusions were obtained as follows. (1) The average copper, iron, and magnesium in the soil profile reduced by 40% from 2012-2013 and the accumulation coefficients varied from 0.14-0.17 to over 0.20; however, the average calcium, potassium, and sodium increased by 33-45%in the soil profile. Calcium and potassium did not gather in the topsoil, whereas sodium under the brackish water treatment changed from none aggregation to strong aggregation. (2) From 2012 to 2013, the total root length density decreased significantly under the brackish water treatment, which led to a sharp reduction of the aboveground dry matter, the numbers of bolls per unit area, and the seed cotton yields (P<0.05). In this case, the root length density, the aboveground dry matter, the numbers of bolls per unit area, and the seed cotton yields got improved by 12-24%(compared to the results of the brackish water treatment) under the alternative irrigation. (3) During the balance stage, solute input through fertilization and output by infiltration were nealy zero, irrigation was the main reason for the variation of Ca2+ and Na+, cotton uptake was the key factor for the variation of Ca2+ and K+, precipitation was responsible for the variation of Cu, Mn, Fe, and Ca2+. After the straw returning to the field, the available content of Cu, Mn, and Fe reduced, whereas the Ca2+, Na+, and K+ increased with the successive planting. (4) Considering the complexity of element transfer processes and the goodness of model performance, CMs can satisfactorily estimate the transport of elements in a typical cotton cultivation ecosystem. (5) The solute transport model coupled with the root solute uptake passed the calibration and validation tests and was suitable for describing solute transport compared to those neglecting the root solute uptake. (6) Under the existing planting patterns, the alternative irrigation was the ideal scheme as its IWP was higher. By reducing the straw returing to the field as well as increcing the fertilization, the control method was suggested that the annual fertilizing amount of Cu, Fe, Mn, and K were 30,52,90, and 862kg/hm2, respectively. These above results provide important theoretical foundations for the rational using of brackish water in arid areas.