Film mulch increases the crop grain yield via topsoil moisture and temperature improvement in cool, semi-arid areas, but little is known about the role of the hydrological and thermic relationship between early and later crop growth seasons in the improving grain yield. We conducted a field experiment to compare polyethylene film mulching (PM) with no mulching (CK) in 2014 and 2015 on the semi-arid Loess Plateau of China. Compared to CK, PM decreased evapotranspiration before the twelve-leaf stage (V12), but increased evapotranspiration after the V12 stage, and significantly increased the topsoil temperature before the six-leaf stage (V6) and the accumulation of soil growing degree days. Corn plants with PM treatment reached the V6 stage earlier, significantly enhancing the contemporary dry matter accumulation. The harvest index, 100-grain weight, and grain yield significantly increased in PM relative to CK in both years. The growing period to the whole growing season evapotranspiration ratio had a negative correlation with the grain yield before the V12 stage, but a positive correlation after the V12 stage. The grain yield had a negative correlation with the air growing degree days (GDD_air) before the V6 stage, but positive correlation from silking to harvest. Conclusively, film mulch promoted the early development of maize via an increased soil temperature before the V6 stage, saved soil water before the V12 stage, resulted in a longer grain-filling period, and increased the GDD_air and evapotranspiration during the grain-filling period, which is key to increasing the maize yield.

Soil organic carbon (SOC) storage and decomposability are crucial for soil quality. Film mulching and phosphorus (P) application are important agricultural practices on the semiarid Loess Plateau. This study analyzed the combined effects of film mulching and P application on SOC, its fractions, and mineralization kinetics under alfalfa (Medicago sativa L.). The six-year field experiment incorporated randomized blocks of split-plot design with two mulching treatments (no film mulching with flat planting and film mulching with ridges and furrows) as main plots and four P levels (P0: 0 kg ha⁻¹, P1: 9.73 kg ha⁻¹, P2: 19.3 kg ha⁻¹, P3: 28.9 kg ha⁻¹) as subplots. Mulching increased SOC content, SOC fractions (light and heavy fraction organic C, microbial biomass C, and dissolved organic C), and mineralization. After six years, mulching increased SOC content by 2.18, 2.60, 2.37, and 0.17 g kg⁻¹ at P0, P1, P2, and P3, relative to no mulching. With increasing P levels, SOC fractions and mineralization increased under no mulching but increased initially and then decreased under mulching. P1 with mulching displayed the highest SOC utilization efficiency and stability. Kinetic models divided SOC into an active and a slow SOC pool, with the latter showing the lowest decomposability and highest stability in P1 with mulching. Overall, film mulching with a low P level, especially 11.9 kg ha⁻¹ P fertilizer, promoted SOC storage under alfalfa on the semiarid Loess Plateau due to the high SOC content with high C utilization efficiency and stability and low decomposability.

Plastic film mulching is widely used in water and temperature-limited regions to enhance crop yields. Phosphorus (P) fertilization can address deficiencies in soil P availability. In this four-year field experiment conducted in an alpine agricultural area, we explored the effects of nitrogen (N) and P supply imbalance on faba bean cultivation, particularly examining intensified N competition between soil microbes and plants. The randomized block design comprised three film mulching treatments—no film mulching with flat planting (NMF), double ridges and furrows mulched with one plastic film (DRM), and three ridges and furrows mulched with one plastic film (TRM)—and three P levels—P₀ (0 kg P ha⁻¹), P₁ (9.10 kg P ha⁻¹), and P₂ (18.2 kg P ha⁻¹). The results indicated that NMF enhanced soil available N and microbial biomass N (MBN) during early growth stages, consequently improving faba bean yield, nodule weight, total N, and microbial biomass carbon (MBC) compared to DRM and TRM. DRM and TRM exhibited higher soil available N and MBN during later growth stages and higher soil temperature and water content, soil water storage (SWS), soil organic C (SOC), and soil C/N ratio than NMF. In NMF and DRM, P fertilization increased grain yield, nodule weight, SOC, total N, soil C/N ratio, soil available N, and MBC but decreased MBN during early growth stages, and decreased soil water content and SWS. TRM exhibited the opposite trend. P fertilization increased soil total P and available P. Overall, NMF combined with P fertilization (~18.2 kg P ha⁻¹) significantly improved faba bean yield. However, it may also accelerate SOC decomposition, highlighting the need to consider N fertilizer application in this alpine agricultural region.