Optimizing irrigation and nitrogen management for potato production under multi-objective production conditions

Abstract: Water is a determining factor in crop production, particularly with the increase of irrigation areas and crops in recent years. Water shortage has posed a great challenge to crop production in North China. Fortunately, the nitrogen (N) fertilizer can serve as another key factor for crop growth and yield formation. However, there is a severe unbalance between the supply of N fertilizer and crop demand. It is also a trade-off between the irrigation and N fertilizer in most parts of Agro-Pastoral Ecotone (APE), which is one of the staple production regions for potatoes in China. Therefore, it is necessary to optimize the irrigation and N management for potato sustainable production using various production goals under different precipitation years. In this study, 27 study sites in the APE were selected to explore the coupling impacts of irrigation and N on the potato yield, Water Use Efficiency (WUE), and economic benefits using the Agricultural Production Systems Simulator (APSIM) Potato model. A two-year field experiment was also carried out under different treatments of irrigation and N fertilizer at a typical site in the APE. Specifically, ten irrigation levels were set in the test, where the deficit values ranged from 10 to 100 mm with the interval of 10 mm, while the application amount of N fertilizer ranged from 30 to 210 kg/hm2 with the interval of 30 kg/hm2. Three types of precipitation years (dry, normal, and wet) were divided in the APE, according to the guarantee rate of precipitation. Subsequently, the WUE was calculated using the ratio of fresh potato yield to evapotranspiration. The economic benefit was the difference between the gross income and the total inputs, where the gross income was the product of the total fresh yield and unit price. Among them, the inputs included the cost of seeding, irrigation, fertilization, use of fungicides and pesticides, tillage, planting and harvesting, and labor. The results showed that the APSIM-Potato model performed well to simulate the phenology, the soil water content of 1m depth, potato N uptake, and yield. The yield of rainfed potato without the application of N fertilizer was ranged from 4 760 to 18 500 kg/hm2, from 9 200 to 20 900 kg/hm2, and from 11 900 to 21 500 kg/hm2 under dry, normal and wet precipitation years, respectively. More importantly, the yields were the lowest in the middle APE under all types of precipitation years. The maximum yield of potato was achieved under the dry year using different combinations of irrigation and N fertilizer. In addition, an optimal combination was achieved to maximize the yield, where the irrigation inputs were 589, 544, and 512 mm in dry, normal, and wet years, respectively, while the N application amounts were all 210 kg/hm2. The irrigation inputs were much higher in the eastern and western APE under all precipitation year types. The maximum WUEs were 85.9, 90.2, and 92.2 kg/ (mm·hm2) in the dry, normal, and wet years, respectively. An optimal combination was also achieved to maximize the WUE, where the irrigation inputs were 172, 107, and 87 mm in the dry, normal, and wet years, respectively, while the amounts of N were 60-120 kg/hm2. Among them, the proportion of sites with 60 kg/hm2 was the highest in the dry years. As such, the maximum economic benefits were 19 340, 18 610, and 18 470 Yuan/hm2 in dry, normal, and wet years, respectively. An optimal combination was also achieved to maximize the income, where the irrigation inputs were 226, 152, and 116 mm in dry, normal, and wet years, respectively, while the application amounts of N were 30-90 kg/hm2 in different year types. The proportion of sites with 90 kg/hm2 was the highest in the wet years. The finding can greatly contribute to formulating optimal management of irrigation and N fertilizer, according to various goals of potato production under different precipitation years.