Effects of irrigation and nitrogen application on soil water and nitrogen distribution and water-nitrogen utilization of wolfberry in the Yellow River Irrigation Region of Gansu Province, China

To address the problems of extensive field management, low productivity, and inefficient water and fertilizer utilization in wolfberry (Lycium barbarum L.) production, an appropriate water and nitrogen regulation model was explored to promote the healthy and sustainable development of the wolfberry industry. Based on a field experiment conducted from 2021 to 2022, this study compared and analyzed the effects of four irrigation levels [75%-85% θf (W0, full irrigation), 65%-75% θf (W1, slight water deficit), 55%-65% θf (W2, moderate water deficit), and 45%-55% θf (W3, severe water deficit)] and four nitrogen application levels [0 kg·ha-1 (N0, no nitrogen application), 150 kg·ha-1 (N1, low nitrogen application), 300 kg·ha-1 (N2, medium nitrogen application), and 450 kg·ha-1 (N3, high nitrogen application)] on soil water distribution, soil nitrate nitrogen (NO3 --N) migration, yield, and water-nitrogen use efficiency of wolfberry. The soil moisture content of the 40-80 cm soil layer was higher than those of 0-40 cm and 80-120 cm soil layer. The average soil moisture content followed the order of W0 > W1 > W2 > W3 and N3 > N2 > N1 > N0. The NO3 --N content in the 0-80 cm soil layer was more sensitive to water and nitrogen regulation, and the cumulative amount of NO3 --N in the soil followed the order of W0 > W1> W2 > W3 and N3 > N2 > N1 > N0 during the vegetative growth period. There was no evidently change in soil NO3 --N accumulation between different treatments during the autumn fruit. The yield of wolfberry under the W1N2 treatment was the highest (2623.09 kg·ha-1), which was 18.04% higher than that under the W0N3 treatment. The average water consumption during each growth period of wolfberry was the highest during the full flowering period, followed by the vegetative growth and full fruit periods, and the lowest during the autumn fruit period. The water use efficiency reached a peak value of 6.83 kg·ha-1·mm-1 under the W1N2 treatment. The nitrogen uptake of fruit and nitrogen fertilizer recovery efficiency of fruit first increased and then decreased with increasing irrigation and nitrogen application. The treatment of W1N2 obtained the highest nitrogen uptake of fruit and nitrogen recovery efficiency of fruit, which were 63.56 kg·ha-1 and 8.17%, respectively. Regression analysis showed that the yield and water-nitrogen use efficiency of wolfberry improved when the irrigation amount ranged from 315.4 to 374.3 mm, combined with nitrogen application amounts of 300.0 to 308.3 kg·ha-1. Additionally, the soil NO3 --N residue was reduced, making it an optimal water and nitrogen management model for wolfberry planting. The present findings contribute novel insights into the production of wolfberry with saving water and reducing nitrogen, which helps to improve the level of wolfberry productivity in the Yellow River irrigation region of Gansu Province and other areas with similar climate.

Water and Nitrogen Coupling on the Regulation of Soil Nutrient-Microbial Biomass Balance and Its Effect on the Yield of Wolfberry (Lycium barbarum L.)

Due to the problems of relatively fragile stability, the quality of soil in the drip-irrigated agricultural ecosystem has high spatial heterogeneity and experiences significant degradation. We conducted a two-year field plot study (2021-2022) in a typical region of the arid zone with the "wolfberry" crop as the research object, with three irrigation and three nitrogen application levels, and the local conventional management as the control (CK). Soil quality under experimental conditioning was comprehensively evaluated based on Principal Component Analysis (PCA) and Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS), and regression analyses were carried out between the soil quality evaluation results and wolfberry yield. The results showed that short-term water and nitrogen regulation enhanced the soil nutrient content in the root zone of wolfberry to some extent, but it did not significantly affect soil carbon:soil nitrogen (Csoil:Nsoil), soil carbon:soil phosphorus (Csoil:Psoil), and soil nitrogen:soil phosphorus (Nsoil:Psoil). When the irrigation quota was increased from I1 to I2, the soil microbial biomass carbon, nitrogen, and phosphorus (Cmic, Nmic, and Pmic) tended to increase with the increase in N application, but the microbial biomass carbon:nitrogen (Cmic:Nmic), microbial biomass carbon:phosphorus (Cmic:Pmic), and microbial biomass nitrogen:phosphorus (Nmic:Pmic) did not change significantly. The comprehensive evaluation of the principal components and TOPSIS showed that the combined soil nutrient-microbial biomass and its ecological stoichiometry characteristics were better under the coupled treatments of I2, I3, N2, and N3, and the overall soil quality under these treatment conditions was significantly better than that under the CK treatment. Under I1 irrigation, nitrogen application significantly increased the yield of wolfberry, while under I2 and I3 irrigation, the wolfberry yield showed a parabolic trend with the increase in nitrogen application. The highest yield was recorded in the I2N2 treatment in the first and second years, with yields of 9967 kg hm-2 and 10,604 kg hm-2, respectively. The coefficient of determination (explained quantity) of the soil quality based on soil nutrient-microbial biomass and the characteristics of its ecological stoichiometry for wolfberry yield ranged from 0.295 to 0.573. These findings indicated a limited positive effect of these indicators of soil on wolfberry yield. The short-term water and nitrogen regulation partly influenced the soil and soil microbial biomass in agroecosystems, but the effect on elemental balance was not significant. Our findings might provide theoretical support for managing the health of agricultural ecosystems.

[Coupling effect of water and nitrogen on mechanically harvested cotton with drip irrigation under plastic film in arid area of western Inner Mongolia, China.]

In order to understand the main and interactive effects of water and nitrogen on crop growth and development, yield, fiber quality, and water-nitrogen use efficiency of mechanically harvested cotton with drip irrigation under plastic film in arid area of western Inner Mongolia, a two-factorial experiment with irrigation water amount and nitrogen dosage in completely randomized block design was conducted in Alxa Left Banner of Alxa League in Inner Mongolia. The levels of water irrigation were 216 mm (W₁), 288 mm (W₂) and 360 mm (W₃), and the nitrogen dosages were 127.5 kg·hm^-2(N₁), 195 kg·hm^-2(N₂) and 262.5 kg·hm^-2(N₃). The results showed that water was the decisive factor for cotton growth, and plant height and dry matter accumulation increased rapidly with increasing the water irrigation level, but the ratio of reproductive organs to shoot biomass decreased. Compared with the treatments W₁ and W₂, the average boll number per plant in W₃ was increased by 25.4% and 17.5%, the seed cotton yield was improved by 18.1% and 11.9%, but the single boll mass was decreased by 5.8% and 4.6%, respectively. It indicated that an increase in boll number per plant was the determining factor in achieving high seed cotton yield. Moreover, there was also a significant interactive effect between water and nitrogen affecting the seed cotton yield. Under the condition with low-level irrigation (W₁ and W₂), the highest seed cotton yield was measured in N₁; while for the condition in W₃, the seed cotton yield in N₂ was greater than that in N₁ and N₃ by 8.5% and 31.9%, respectively. In general, the regulation of water and nitrogen had no significant effect on fiber quality. Water use efficiencyin W₁N₁ was 1.37 kg·m^-3, which was not significantly different with the value in W₃N₂, and the nitrogen partial factor productivityin W₃N₁ was the maximum (51.35 kg·kg^-1). Therefore, irrigation had a significant effect on yield increasing, but nitrogen application promoted the seed cotton yield only under well-watered conditions. The treatment with irrigation amount of 360 mm and nitrogen fertilizer of 195 kg·hm^-2 could promote the shoot biomass accumulation significantly and achieve the highest seed cotton yield, and its water use efficiency and nitrogen partial factor productivity were 1.37 kg·m^-3 and 36.41 kg·kg^-1, respectively, indicating the potential of water-saving and yield increasing. Therefore, it was recommended as a suitable water and nitrogen management for the mechanically harvested cotton in arid area of western Inner Mongolia.