This 2-year field study analyzed plastic film mulching (PFM) effects on nitrogen use efficiency (NUE), and soil N pools under rainfed dryland conditions. Compared to no-mulching (NM, control), maize yields under PFM were increased by 36.3% (2515.7 kg ha⁻¹) and 23.9% (1656.1 kg ha⁻¹) in the 2020 and 2021 growing seasons, respectively. The PFM improved (p < 0.01) the water use efficiency (WUE) of maize by 39.6% and 33.8% in the 2020 and 2021 growing seasons, respectively. The 2-year average NUE of maize under the PFM was 40.1, which was 30.1% greater than the NM. The average soil total N, particulate organic N, and microbial biomass N contents under the PFM soil profile were increased by 22.3%, 51.9%, and 35%, respectively, over the two growing seasons. The residual ¹⁵N content (%TN) in soil total N pool was significantly higher (p < 0.05) under the PFM treatment. Our results suggest that PFM could increase maize productivity and sustainability of rainfed dryland faming systems by improving WUE, NUE, and soil N pools.

Soil extracellular enzymes are pivotal for microbial nutrient cycling in the ecosystem. In order to study the effects of different nitrogen application rates under plastic film mulching on soil extracellular enzyme activities and stoichiometry, five nitrogen application levels (i.e., 0, 90, 150, 225 and 300 kg·hm⁻²) were set based on two treatments: plastic film mulching (PM) and no film mulching (LD). We measured the soil extracellular enzyme activities (EEAs) and stoichiometry (EES) of four enzymes (i.e., β-1,4-glucosidase (βG), leucine aminopeptidase (LAP), β-1,4-N-acetylaminoglucosidase (NAG) and alkaline phosphatase (AP)) involved in the C, N and P cycles of soil microorganisms in surface soil at five maize growth stages (seedling stage, jointing stage, trumpet stage, grout stage and harvest stage). The results showed that there were significant differences in soil EEA at different maize growth stages. The soil nutrient content and soil EEA were significantly improved under PM, and the stoichiometric ratio of extracellular enzymes (E_C:N:P) was closer to 1:1:1, which indicated that PM was beneficial to the balance of soil nutrients and the activity of microorganisms. At each stage, with the increase in nitrogen application levels, the soil EEA showed a trend of increasing first and then decreasing (or remained unchanged), and both LD and PM treatments reached their highest activity at the 225 kg·hm⁻² nitrogen application rate. When the nitrogen application level was less than 225 kg·hm⁻², the soil enzyme activity was mainly limited by the N nutrient, and when the nitrogen application level reached 300 kg·hm⁻², it was mainly limited by the P nutrient. RDA and correlation analysis showed that the soil C:P, C:N, N:P and pH had significant effects on soil βG, NAG + LAP and AP activities as well as E_C:N, E_C:P and E_N:P.

Nitrogen (N) fertilization plays a pivotal role in the nitrogen transport process and yield formation of field-grown Tibetan barley (Hordeum vulgare L., qingke in Chinese); however, little is known about its interaction with irrigation regimes. Here, we performed a control experiment to investigate the effects of irrigation regimes (primary irrigation and double irrigation, mentioned as W1 and W2) and N levels (0, 90, 120, and 150 kg ha⁻¹, mentioned as N0, N9, N12, and N15) on the nitrogen accumulation, translocation, and utilization of Tibetan barley in the Tibetan Plateau during the spring barley seasons in 2022. The results showed that the highest yield (6242.28 kg ha⁻¹) and aboveground biomass (12,354.13 kg ha⁻¹ for anthesis; 15,827.9 kg ha⁻¹ for maturity) were achieved in W2N15 as compared to other treatments. The maximum grain N accumulation (117.66 kg ha⁻¹), the N translocation (54.16 kg ha⁻¹), and the post-anthesis N accumulation (63.5 kg ha⁻¹) were achieved in the W1N15 treatment. The N utilization efficiency increased with irrigation frequency and decreased with N application; however, the conclusion given by the N agronomic efficiency is contrary to this trend. The grain yield had significant positive correlations with the grain N accumulation (W1: r = 0.98; W2: r = 0.97) and N translocation (W1: r = 0.84; W2: r = 0.94), but significant negative correlations with the N harvest index (W1: r = −0.95; W2: r = −0.95) and N utilization efficiency (W1: r = −0.9; W2: r = −0.85). The path analysis revealed that the factors related to N utilization (β = 0.875) and the factors related to N translocation (β = −1.426) were the significant direct contributors towards grain yield. The influence of N application (total effect = 0.922) on the grain yield was much stronger than that of the irrigation regime (total effect = 0.324). Our findings can guide future efforts in designing sustainable water and N fertilizer management strategies for Tibetan barley in the Tibetan Plateau.

As plastic mulching is widely used for maize production on Loess Plateau, study of the fate of fertilizer nitrogen (N) in rain-fed croplands is of great significance. Field experiments were conducted during 2015–2016 at a typical dry-land farm on the Loess Plateau, China. The stable isotope tracer technique was applied to analyze the effects of plastic mulching on the maize crop yield, N content in the grain, and mechanism of N uptake and utilization in maize plants with plastic mulch (PM) and without plastic mulch (CK) on the Loess Plateau. Maize yield, aboveground dry matter, grain N concentration, and N uptake in aboveground biomass for PM significantly increased, in addition to fertilizer nitrogen recovery and nitrogen production efficiency. Compared to CK, PM improved the total N uptake from the soil in the aboveground biomass by 16.39 and 27.75 kg ha⁻¹ and fertilizer nitrogen recovery by 10.89 and 22.02 kg ha⁻¹, respectively. Furthermore, PM increased in-season fertilizer N retention in the soil by 11.9–24.8 kg ha⁻¹, and the uncountable fertilizer N decreased by approximately 33.8 kg ha⁻¹ on average. In conclusion, PM simultaneously improved the maize yield and N utilization, which provides a scientific basis for nitrogen management in maize croplands.