Coupling scheme of water and fertilizer based on yield, quality, use efficiency of water and fertilizer in bag pepper growing

This study aims to establish a precise management model of water and fertilizer, in order to clarify the coupling effect of water and fertilizer on yield, fruit quality, water use efficiency (WUE) and fertilizer use efficiency (FUE) for pepper planting in bag. Taking "Bolong (37-94) Bolon RZ F1" pepper as the test material, 18 coupling treatments were conducted, with three levels of irrigation (control the relative water content of substrate in 70%-75% (W1), 55%-60% (W2), and 40%-45% (W3)), three levels concentration of nutrient solution (set up 150% (F1: each plant supplies N-P2O5-K2O, 8.42-3.96-13.93 g), 100% (F2: each plant supplies N-P2O5-K2O, 7.41-3.48-12.26 g), 80% (F3: each plant supplies N-P2O5-K2O, 6.36-2.99-10.53 g) Yamazaki pepper nutrient solution formula), and two supply amounts of nutrient solution (regular supply; reduce supply, where six days before each harvest reduced 40% nutrient solution supply). Randomized block design was used in the whole experiment, which was repeated for three times, where each block was 7 m×1.2 m with 24 plants. Pepper seedlings with five leaves were transplanted into the matrix bag, with 60 cm row spacing and 30 cm plant spacing, on March 20, 2019, and uprooted on July 28, 2019. A handheld matrix moisture meter (HH150, Delta-T Devices LTD, UK) was used to determine the relative moisture content of matrix. The irrigation was carried out according to the measured data at 8:00 am every day, whereas, the frequency of nutrient solution supply was once every two days, as well as the water and fertilizer integrated drip irrigation system was used for water and fertilizer management. A multi-objective model of yield, comprehensive fruit quality, WUE and FUE was established, according to the obtained data of the factors and the coupling effects, and then to be optimized using the genetic algorithm. The results showed that the single factor of irrigation, nutrient solution concentration, and their coupling effect can pose a significant influence on the yield, WUE and FUE of pepper. Specifically, the yield, WUE and FUE all increased first, and then decreased with the increase of irrigation and nutrient solution concentration. A Topsis method was used for the comprehensive evaluation of fruit quality. The reduction of nutrient supply amount before pepper fruit harvest can maintain the higher yield and WUE, while significantly improve the quality of pepper fruit and FUE. The combined W2F2 treatment under a reduced supply of nutrient solution can achieved the largest yield, WUE and FUE, whereas, the W2F1 treatment under a reduced supply of nutrient solution has showed the optimal comprehensive evaluation of fruit quality. The optimal coupling scheme of water and fertilizer was obtained using the genetic algorithm multi-objective optimization method, where the combined W2F2 treatment under a reduction supply of nutrient solution was the best management model. The specific coupling scheme of water and fertilizer can achieved high yield and quality of pepper in bag: Irrigation according to the relative moisture content of substrate 55%-60%, applying 100% Yamazaki pepper nutrient solution formula, and six days before each harvest reduced 40% nutrient solution supply. The pepper yield can reach 87 930.52 kg/hm2, where the fitness of fruit quality comprehensive evaluation reached 0.749, the WUE and FUE were 41.14 kg/m3 and 38.83%, respectively. The findings can provide an insightful guidance for high yield and quality of pepper production, and further for the scientific management of water and fertilizer in pepper farming.