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【Objective】 Nutrient uptake and its use efficiency by crops are modulated by many biotic and abiotic factors, and the objective of this paper is to investigate their change in response to planting density and irrigations amount in attempts to provide a guidance to help improve water use efficiency and reduce fertilizer usage without compromising crop yield. 【Method】 The experiment was conducted in a field in an arid warm valley in Yunnan province, with onion used as the model plant. We compared three irrigation amounts: 7 000 m3/hm2(I1), 4 550 m3/hm2 (I2) and 3 300 m3/hm2 (I3), and two planting densities: 21 200 plants/hm2 (D1) and 118 800 plants/hm2(D2). In each treatment, we measured the biomass and bolting percentage of the onion, its nutrient absorption and utilization, harvest traits, as well as water use efficiency (WUE). 【Result】 Irrigation amount had a significant effect on WUE, nutrient absorption and utilization efficiency. Compared with other irrigation treatments, I1 increased the uptake of P, K and Mg by the crop, but the use efficiencies of these minerals in I3 were the highest. Planting density also significantly affected biomass, bolting percentage, nutrient absorption and utilization efficiency of the crop. Compared with D2, D1 increased the uptake efficiency of N, P and Mg by the crop, whilst their utilization efficiency was higher in the D2. It was found D2 significantly increased the biomass but reduced the bolting percentage of the crop. We found irrigation amount and planting density interactively affected biomass, bolting percentage, WUE, nutrient absorption and utilization efficiency, harvest traits, absorption efficiency of N, P, K, Ca and Mg, with most of these entities peaking in I1+D1. The principal component analysis gave the highest score to I3+D2 followed by I1+D1. 【Conclusion】 Comparison of various combinations of irrigation amounts and planting densities revealed that I3+D2 was optimal for growing onion in the arid warming valley studied in this work.

【Objective】Cultivation of sweet corn has increased over the past decades in some areas of China, but its demand for water and the associated irrigation strategies are poorly documented. The objective of this paper is to plug this knowledge gap. 【Method】A two-year field experiment designed based on the principle of achieving high yield was conducted. During the experiment we measured the change in soil moisture and meteorological factors, and used them to calculate water requirement, water consumption and crop coefficient (kc) of the crops. These help us to optimize the irrigation strategy for sweet corn production. 【Result】The water requirement, daily water consumption during the growth season of the sweet corn in 2016 and 2017 were 197.7 and 212.9 mm, 3.0 mm/d and 3.1 mm/d respectively. The daily water consumption varied with growth stage, being highest in the tasseling stage and least in the seedling stage. The average crop coefficient in 2016 and 2017 was 0.63 and 0.67, respectively, and the optimal calculation showed that changing irrigations times to four could reduce irrigation water by 31.84% to 33.97% compared to the currently used irrigation strategy. 【Conclusion】Water requirement of the sweet maize was low and its water consumption was similar to normal corn. Appropriate irrigation is essential to safeguarding its production.

This study is conducted to further review the rationality of the standard for rice irrigation quotas in Jianshui of southern central Yunnan.On the basis of the observation data of Jianshui Meteorological Station from 1958 to 2013 and the rice-season test results of irrigation test sites in Jianshui from 2016 to 2018,the crop and soil parameters in the CROPWAT model are calibrated,and the processes of water in the rice soaking stage and irrigation amount in the prime field stage are simulated.With frequency arrangement results of irrigation amount in the whole growth stage,the rice irrigation schedule is drafted by the typical-year method.The results indicate that under the irrigation probability (P) of P=50%,P=75%,and P=90%,the irrigation quota of Jianshui rice in the whole growth stage is 510.1,591.1,and 651.2 mm,respectively,including the quota for the rice soaking stage of 185.3,209.2,and 213.9 mm,as well as the quota for the prime field stage of 324.8,381.9,and 437.3 mm,respectively.The irrigation frequency in the prime field stage is 8,9,and 10 times,respectively,and the irrigation quota is between 20.3 to 46.7 mm.The standard for rice irrigation quotas in Jianshui of southern central Yunnan is between 240.0 to 255.0 mm in the rice soaking stage,and under the conditions of P=50%,P=75%,and P=90%,the rice irrigation quota in the prime field stage is 427.5~435.0,487.5~502.5,540.0~562.5 mm,respectively.The current standard for rice irrigation quotas is basically reasonable,but from the viewpoint of water conservation and protection,there is still some water-saving space for rice irrigation.