Effects of sowing date, water and nitrogen coupling management on cane yield and sugar content in sugarcane region of Yunnan

Sugarcane is a staple sugar crop with a consistently large planting area in Dehong, a humid sugarcane region in Yunnan province, but data are lacking on the interaction effects of sowing date, water (rainfed and irrigated), and nitrogen management on sugarcane production. In this study, the suitability of APSIM-Sugar model (version 7.8) in a humid sugarcane region in Yunnan province was tested based on sequential sowing date experiments conducted at Ruili experimental station in Dehong. Sowing date experiments of sugarcane planting in winter were used for model calibration while sowing date experiments of sugarcane planting in spring were used for model validation. Genetic parameters for 2 sugarcane varieties YZ0551 and ROC22 were derived with trial-and-error method. Using the validated APSIM-Sugar model long-term simulation experiments were designed to evaluate the impacts of coupled sowing date, water and nitrogen management on sugarcane production in Yunnan. Three typical sowing dates were used for sugarcane planting in spring, summer, autumn and winter, i.e. February 20, March 20 and April 20 for sugarcane planting in spring, May 20, June 20 and July 20 for sugarcane planting in summer, August 20, September 20 and October 20 for sugarcane planting in autumn, November 20, December 20 and January 20 for sugarcane planting in winter. We compared different evaluation indices, such as sugarcane yield, sugar content, water, and nitrogen use efficiency, to determine optimal cultivation management options for rainfed and irrigated sugarcane production. The study results confirmed that the APSIM-Sugar model performed well in simulating sugarcane yield and sugar content with normalized root mean squared error (NRMSE) less than 10% and R2 more than 0.9. Suitable sowing date and optimal management of water-nitrogen could improve significantly sugarcane yield, sugar content, water use efficiency and nitrogen use efficiency in Yunnan Province. Sufficient base fertilizer and appropriate irrigation were the 2 key factors in ensuring high sugarcane yield. However, nitrogen use efficiency decreased significantly when nitrogen fertilizer was applied excessively. Especially under water limited conditions, increasing nitrogen application rate did not increase sugarcane yield, and even led to the decrease of cane yield and sugar content. Planting sugarcane under the suitable sowing date, the natural precipitation in a humid sugarcane production region could meet the water demand during seedling and maturity stages of sugarcane. Irrigation at tillering stage could improve significantly the yield of autumn and winter planting sugarcane while irrigation at elongation stage could be beneficial on the growth of sugarcane planting in spring, summer and autumn season. Water requirement of sugarcane during the whole growth period was generally 1000-1200 mm and therefore supplementary irrigation of 180-720 mm was needed for growth and development of sugarcane. Applying base fertilizer plus additional fertilizer could not improve sugarcane yield compared with applying base fertilizer only. Therefore, applying sufficient base fertilizer at sowing was conducive to cost-saving and efficiency-increasing. In order to ensure higher water-nitrogen use efficiency, the reasonable application amount of nitrogen fertilizer for rainfed sugarcane field was 60-120 kg/hm2, and that for irrigated sugarcane field was 120-180 kg/hm2. Under rainfed condition, planting in spring or winter would probably ensure stable sugarcane yield with high water use efficiency and agricultural efficiency of nitrogen. Simulations predicted sugarcane yields of about 95-100 t/hm2 and 19% sugar if planted in late February or late December with 60 kg/hm2 nitrogen and no irrigation. If irrigation was possible, sugarcane planted in spring or autumn would lead to high yield and high water use efficiency and agricultural efficiency of nitrogen. Simulations predicted sugarcane yields of about 120-170 t/hm2 and 17%-18% sugar for planting in late February or late October with 120-180 kg/hm2 nitrogen and 360-720 mm irrigation. These results provide supports for improving sugarcane high efficiency production and manage decision by optimizing sowing date, irrigation, and nitrogen management, especially in a humid sugarcane planting region of Yunnan.