The efficiency of irrigation, as well as optimization of nutrients, affect spinach yield in all growth stages. In this study, the sensitivity of spinach (early and mature yields) to shallow saline groundwater and the effect of fertigation treatments on mature yield were experimentally investigated. The sprinkler irrigation experiments were conducted on 0.47 ha of silty clay soil at the University of California Desert Research and Extension Center (DREC) in Imperial Valley, California. Twelve beds in the experimental field were chosen randomly to investigate the effect of three fertigation treatments on spinach yield. Three rates of urea ammonium nitrate (UAN-32) fertilizer; T₁: 200 kg ha⁻¹ (150%), T₂: 133.3 kg ha⁻¹ (100%), and T₃: 66.7 kg ha⁻¹ (50%) in four replicates were applied. Soil samples to depths of up to 120 cm were collected at baby leaves and mature harvesting dates (17th October and 19th November 2019, respectively) for salinity measurements. Additionally, soil matric potential through the 120 cm soil depth was measured and groundwater levels in five observation wells were recorded during the growing season. Results showed that average soil salinity at baby leaves harvesting stage through the top 60 cm active root zone depth ranged from 0.61 to 1.48 dS m⁻¹, which is lower than the spinach salinity threshold limit (2 dS m⁻¹), while the average groundwater depth was 1.90 m with salinity ranging from 6.35 to 10.60 dS m⁻¹. Correlation analysis showed that the baby spinach leaves yield was weakly correlated (r = 0.40) to the average soil salinity in the top 60 cm soil depth. Although groundwater and top 60 cm soil salinity showed an increase at the mature yield harvesting stage, the mature yield was weakly correlated to soil salinity (p = 0.116). As the UAN-32 rate increased, the mature spinach yield increased. The mature spinach yields were 17.31, 14.00, and 12.54 ton ha⁻¹ for T₁, T₂, and T₃ fertigation treatments, respectively. However, only a 10% reduction in yield occurred in T₃ treatment corresponding to a 50% reduction in UAN-32 rate by 66.7 kg ha⁻¹. Based on the results of this study, shallow saline groundwater has little impact on spinach yield. In addition, the 50% increase in UAN-32 rate had a significant impact on mature spinach yield. The 150% UAN-32 rate resulted in an increase in spinach yield and could be used in arid and semiarid regions with similar conditions to the Imperial Valley but additional measures to minimize the leaching of nitrate from the root zone and to reduce the load of nitrogen in drainage water are needed to minimize the potential negative impact of over-fertigation on the environment.

灌溉效率以及营养成分的优化会影响所有生长阶段的菠菜产量。在这项研究中，菠菜（早期和成熟产量）对浅层咸水地下水的敏感性以及施肥处理对成熟产量的影响进行了实验研究。喷灌实验是在加州帝国谷的加州大学沙漠研究与推广中心 (DREC) 的 0.47 公顷粉质粘土上进行的。随机选择试验田12张床位，研究3种施肥处理对菠菜产量的影响。三率尿素硝酸铵（UAN-32）肥；T ₁ : 200 kg ha ^-1 (150%), T ₂ : 133.3 kg ha ^-1 (100%), 和 T₃：在四次重复中施用66.7 kg ha ^-1 (50%)。在幼叶和成熟收获日期（分别为 2019 年 10 月 17 日和 11 月 19 日）收集了深度达 120 厘米的土壤样本，用于盐度测量。此外，测量了 120 厘米土壤深度的土壤基质势，并在生长季节记录了五个观测井中的地下水位。结果表明，幼叶收获期至顶部 60 cm 活动根区深度的平均土壤盐度范围为 0.61 至 1.48 dS m ^-1，低于菠菜盐度阈值（2 dS m ^-1），而平均值为地下水深度为 1.90 m，盐度为 6.35 至 10.60 dS m ^-1. 相关分析表明，幼菠菜叶片产量 与表层60 cm土壤深度的平均土壤盐度呈弱相关（r = 0.40）。尽管地下水和前 60 cm 土壤盐分在成熟产量收获阶段显示出增加，但成熟产量与土壤盐分的相关性较弱（p  = 0.116）。随着 UAN-32 比率的增加，成熟菠菜产量增加。T ₁、T ₂和T ₃施肥处理的成熟菠菜产量分别为17.31、14.00和12.54吨ha ^-1。然而，在 T ₃处理中仅发生了 10% 的产量降低，对应于 UAN-32 率降低 50% 66.7 kg ha ^-1. 根据本研究的结果，浅层咸水地下水对菠菜产量影响不大。此外，UAN-32率增加50%对成熟菠菜产量有显着影响。150% 的 UAN-32 率导致菠菜产量增加，可用于干旱和半干旱地区，其条件与帝王谷相似，但采取了额外措施以最大限度地减少根区硝酸盐的浸出并减少氮负荷需要排水，以尽量减少过度施肥对环境的潜在负面影响。