The water-fertilizer coupling study of high protein soybean-based on uniform design and partial least squares regression modeling

To study the best water-fertilize model of high protein soybean, taking the high protein soybean Qihuang 34 as the test material, the effect of water-fertilizer coupling on growing development, dry matter accumulation, yield and quality of soybean was studied in this experiment. The uniform design testing was employed and six combinations with four factors of water, nitrogenous, phosphate and potash fertilizer were set. In addition, the mathematical model of the results was analyzed by partial-least regression (PLS), with the production as a dependent variable, four factors as independent variables, to explore the best water-fertilizer model for high protein soybean. The results showed that the plant growth period was longer under high (100%) or low water (20%, 36%), shorter under suitable water (52%, 64%), which greatly influenced by water. The node numbers of main stem was less affected by water-fertilizer coupling with effective pod numbers, pod length and the effective branch numbers were all lower under high (100%) or low water (20%, 36%). The dry matter accumulation of root, stem, leaf, petiole, and pod were all affected by different water-fertilizer coupling, which showed poor performance under high or low treatment (T1, T2, T6), better under suitable treatment (T3, T4), and the correlation coefficient between protein and fat in grain was -0.93'*'*, which indicated significant negative correlation. Grain weight per plant, hundred-grain weight and grain number per plant were all highest at suitable treatment (T3), and that all had significantly positively related to yield with correlation coefficient of 1.00'*'*, 0.98'*'*,0.89'*'* respectively, indicating that the suitable water-fertilizer coupling accelerated the transfer of nutrients to the grain, then increased the grain number and grain weight, further increased grain yield. Moreover, the mathematical model PLS indicated that the yield of soybean was strongly dependent on water supply; sufficient water supply significantly increased the yield and plant height of soybean. When the soil relative water content was 47.6%, the application of nitrogenous fertilizer, phosphate fertilizer and potash fertilizer were separately at 70 mg · kg^-1, 100 mg · kg^-1 and 111.57 mg · kg^-1, and the optimal output of soybean yield was 5121.26 kg · hm^-2. This study offers theoretical guidance and technical support for high quality and efficient production of high protein soybean, also provides a reliable theory basis for the application of uniform design in agricultural field. (authors)