Given the shortage of water resources and excessive application of nitrogen fertilizers in irrigated areas, we explored the effect of water–nitrogen coupling on soil microbial diversity in maize fields irrigated using shallow buried droppers. A field experiment (split-plot design) was used with irrigation amounts set at 40%, 50%, and 60% of the conventional amount; furthermore, 13 water and nitrogen coupling treatments were designed. The secondary area was the nitrogen application level, corresponding to 50%, 70%, and the original conventional application amounts. The results showed that the effect of irrigation amount on bacterial community composition was greater than that of nitrogen, whereas the effect of nitrogen on fungi was greater than that on bacteria. No significant difference was detected in the α diversity index or species richness of bacteria and fungi. Available phosphorus and organic carbon contents significantly correlated with the community structure of soil bacteria (p < 0.05). The relative abundances of bacteria and fungi were stable with the decrease of nitrogen application rate at the irrigation rate of 2000 m³ ha⁻¹. With the decrease of irrigation amount, the relative abundance of bacteria and fungi was stable under the treatment of 210 kg ha⁻¹ nitrogen fertilizer. Moreover, the relative abundance of nitrogen-fixing bacteria related to the nitrogen cycle was increased by irrigation of 2000 m³ ha⁻¹ and nitrogen application of 210 kg ha⁻¹. Moderate reduction of subsequent N supply should be as a prior soil management option in a high N input agroecosystem.

Reduced fertilizer efficiency caused by excessive use of nitrogen (N) fertilizer is a major problem in agriculture and a hot topic of research. Most studies have focused on the effect of N application rate on N efficiency, whereas there are limited studies on changing the N form to improve N yield and efficiency. Here, the effects of different N application rates and nitrate-to-ammonium N ratios on post-anthesis carbon (C) and N metabolism and maize yield under shallow-buried drip irrigation were investigated. Two rates of N application (210 kg·ha⁻¹ (NA1) and 300 kg·ha⁻¹ (NA2)) and three nitrate-to-ammonium N ratios (2:1 (NF1), 3:1 (NF2), and 4:1 (NF3)) were utilized. Post-anthesis photosynthetic characteristics, activities of key enzymes in photosynthetic C and N metabolism, nonstructural carbohydrate content, post-anthesis N accumulation and transportation, yield, and N-use efficiency were determined. At both N application rates, NF2 treatment enhanced photosynthetic activity in the ear-leaf at silking stage and promoted key enzyme activities of C and N metabolic pathways, compared with NF1 and NF3. Furthermore, NF2 significantly increased nonstructural carbohydrate accumulation (4.00–64.71%), post-anthesis N accumulation and transportation (11.00–38.00%), and grain yield (2.60–13.08%). No significant differences between NA1 and NA2 were observed under NF2 in most of the measured variables; however, NA1 had higher N-use efficiency. Thus, the optimal treatment under shallow-buried drip irrigation was a N application rate of 210 kg ha⁻¹ and a nitrate-to-ammonium N ratio of 3:1. These findings provide theoretical guidance on appropriate N applications for high-yield maize production.

Biochar application can alter soil properties and enhance soil quality. However, the effects of the regulatory mechanisms underlying nitrogen fertilizer application on soil physicochemical properties and microbial characteristics remain unclear. We conducted a three-year maize field experiment to investigate the effects of four biochar application rates (0, 8, 16, and 24 t/ha) and three nitrogen fertilizer rates (0, 150, and 300 kg/ha) on soil physicochemical properties, enzyme activities, microbial community structure, and maize yield. In the 0–20 cm soil layer, the combined application of biochar and nitrogen fertilizer significantly increased soil porosity (SP) and soil water content (SWC), reduced soil bulk density (SBD), and increased soil organic carbon (SOC) and total nitrogen (TN) levels. Additionally, β-D-cellobiohydrolase and leucine aminopeptidase activities were enhanced, along with nitrogen acquisition potential. The relative abundance of Proteobacteria was highest at a biochar application rate of 16 t/ha. The combined 16 t/ha biochar and 150 kg/ha nitrogen treatment exhibited the highest maize yield. Maize yield was positively correlated with SP, SWC, SOC, and TN. Consequently, the combined application of 16 t/ha biochar and 150 kg/ha nitrogen improved soil physicochemical properties, enhanced soil enzyme activities, regulated key soil microbial taxa, and increased maize yield.

A field research was conducted in the Agricultural High-tech Demonstration Park in Horqin District of Tongliao, Inner Mongolia, using the maize variety Nonghua 101 with two cropping modes, including strip-till with staggered planting (seeding strip tillage, 15 cm + 45 cm narrow-double row staggered sowing, TGCW) and conventional tillage with equal row space (rotary tillage with row space of 60 cm, CK), and three planting densities (67,500 plants hm^–2, 82,500 plants hm^–2, and 97,500 plants hm^–2) in 2017 and 2018 to study the effect of strip-till with staggered planting on regulating spring maize yield formation and coordination characteristics of shoot-root in irrigation areas of Xiliao river plain. The model of that strip-till with staggered planting enhanced maize yield by 13.1% and 13.8% in 2017 and 2018, under the planting density 82,500 plants hm^–2 compared with CK, respectively. The strip-till with staggered planting showed a distinct advantage on the amount and rate of dry matter accumulation after silking, which obviously delayed the senility of leaves in later growth stage, meanwhile, compared with CK, the light transmittance significantly increased in or above panicle layers. The leaf area index, net photosynthetic rate and population photosynthetic potential in the model of strip-till with staggered planting were higher than those in CK in late growth stage. At later growing stage, the strip-till with staggered planting had significantly higher root dry weight than CK in different soil layers, with the highest root ratio in 20–60 cm, especially under higher planting density. The grain yield against per unit of root weight at silking and root-shoot ratio at maturity had a distinct advantage. In conclusion the strip-till with staggered planting combined with high planting density can increase light transmission rate in above-spike layer in late growing stage, alleviate leaf area decline, increase production capacity, facilitate root growth and increase root ratio in deeper soil layers. Shoot-root coordination under dense planting is one of the main reasons facilitating yield increase of spring maize in irrigation areas of Xiliao river plain.

In order to explore the effects of shallow drip irrigation on the yield and root decay characteristics of spring corn after silking, in the Agricultural and Animal Husbandry High Tech Demonstration Park of Horqin District, Tongliao City from 2017 to 2020, traditional border irrigation conventional nitrogen application (W: 4000 m3 hm-2, N: 300 kg hm-2) was used as the control (CK), and drip irrigation quotas were used as the main treatments. Three levels of traditional border irrigation conventional irrigation were set: 40% (W1: 1600 m3 hm-2), 50% (W2: 2000 m3 hm-2), and 60% (W3: 2400 m3 hm-2), Using nitrogen application rate as the secondary treatment, three levels of conventional nitrogen application rate [50% (N1: 150 kg hm-2), 70% (N2: 210 kg hm-2), and conventional nitrogen application rate (N3: 300 kg hm-2)] were set up to determine the changes in spring maize yield under different water and nitrogen treatments. In 2019 and 2020, the BTC-100 micro root monitoring system was used to continuously monitor root system of spring maize in the 0-100 cm soil layer at the 0-50 days stage after silking. The results showed that the yield of spring maize was significantly higher in W3N3 than CK for four consecutive years, and there was not significant difference compared with W3N2, W2N3, and W2N2 treatments. The nitrogen agronomic efficiency of W3N2 was also the highest at the same time. Compared with CK, root length density, the total root surface area, and the average root diameter of W3N3 all increased in 0-60 cm soil layer while root length density, the total root surface area, and the average root diameter were less in 80-100 cm soil layer; the decrease in root length density, the total root surface area, and the average root diameter was lower from 0 d to 50 d after silking in two years, in which the root length density of W3N3 and CK decreased by 10.29% and 8.83%, and 15.04% and 14.08% and the average root decay rate of W3N3 decreased by 5.23% and 4.43% compared with CK. Under the shallow buried drip irrigation, the root length density, the average diameter, and the total root surface area of W3N3 and W3N2 were both higher than those of other treatments, whose decrease extent of average root decay rate were lower in 0-60 cm soil layer and differences were less in 80-100 cm soil layer from 0 day to 50 days after silking; During the 0-50 day stage after silking, the difference of average root decay rate between W3N3 and W3N2 was not significant, and W3N2 decreased by 5.68% and 5.44%, 9.75% and 11.98%, 7.16% and 6.77%, respectively, compared with W3N1, W2N2, and W1N2 in two years. The variance analysis showed that both drip irrigation and nitrogen application had a significant impact on yield and nitrogen fertilizer agronomic efficiency. The drip irrigation amount had a significant impact on the root length density, the total root surface area, and the average root decay rate of the 0-60 cm soil layer at the 0-50 day stage after silking. Nitrogen application amount had a significant impact on root length density of the 0-60 cm soil layers at the 0-50 day stage after silking, the total root surface area of the 0-60 cm soil layers at the 0-30 day stage after silking, and the average root decay rate of the 0-40 cm soil layer at the 0-50 day stage after silking. In summary, the root length density, the total root surface area, and the average root diameter of the 0-60 cm soil layers of W3N3 and W3N2 under shallow burying drip irrigation were relatively higher, and the decrease was lower within the 0-50 day stage after silking, the average root decay rate was low, and the yield difference between the two was not significant, however, W3N2 had higher nitrogen agronomic efficiency, which could be recommended as a suitable water and nitrogen application mode for water-saving, high-yield, and efficient cultivation of corn for the irrigation area of the Xiliaohe plain.