The efficient nutrient management is essential for agricultural green development. With the increase of farm land scale and the development of agricultural mechanization, the mismatch between agricultural machinery and agronomy in nutrient management becomes increasingly obvious. There is a requirement to coordinate agronomic techniques and machinery operation. This paper analyzed the current situation and improvement direction in nutrient management techniques and agricultural machinery in the cropping system of spring maize in northeast China, winter wheat-summer maize in north China, and rice planting system in south China. It is indicated that efficient fertilizer application technology needs suitable fertilizer application machinery as guarantee, new fertilizer products need new fertilizer application machinery, changing cultivation and tillage methods generates new demand for agricultural machinery, and fertilizer application mechanization to be upgraded by using information and automatic intelligent techniques. At the same time, the fertilizer products and fertilizer application technology innovation need to take into consideration of the feasibility of mechanization. This paper described the research progress of starter fertilizer, synchronized fertilizer application and sowing technology, and straw mulching strip tillage technology in maize, within-season mechanized fertilizer application technology in wheat, mechanized side-depth fertilizer application technology in rice, and mechanized variable fertilizer application technology in China. The suggestions were provided to enhance the integration of agricultural machinery and agronomic technology, so as to upgrade the level of nutrient management of field crops.

Strip-till (ST), including straw mulching in the inter-row and localized fertilization in the intra-row, is a conservation tillage system for improving soil quality and crop growth. However, the yield advantage of maize under ST compared to conventional tillage (CT) remains unstable, and the strategies to increase maize yield under ST are unclear. This study aims to understand the physiological mechanism underlining maize yield formation under ST by comparing two maize cultivars, DKM753 and DK517, with contrasting yield performance in ST versus CT systems. Compared to CT, ST resulted in a 4.5% yield increase for DKM753 but a 5.6% decrease for DK517. These yield differences were primarily attributed to variations in grain number per ear (GN). During the rapid growth stage (V14-R3), i.e., two weeks before and after silking, DKM753 showed a 6.7% increase in maximum growth rate (V_max) and a 6.3% increase in average growth rate (V) under ST, whereas DK517 exhibited decline of 8.5% in V_max and 12.3% in V. Significant positive correlations are observed between V_max and V with GN under ST (R² = 0.79 and R² = 0.90, respectively). Enhanced dry matter accumulation in DKM753 under ST was attributed to increased leaf expansion rates, contributing to a larger photosynthate source. The straw mulching and localized nitrogen fertilization increased root-zone nitrogen availability at silking in ST compared to CT. DKM753 had a greater root system which made better use of the soil N and lead to an increased leaf nitrogen accumulation by 14.9% under ST. It is concluded that maize yield under the strip-till system is determined by grain number per ear, which can be increased by increasing nitrogen accumulation, plant growth, and ear development around silking stage. A sound root system can efficiently utilize soil nitrogen resources under the strip-till system, increasing plant nitrogen accumulation and thereby promoting plant growth.

Nitrogen (N) deficiency is one of the main factors limiting maize (Zea mays L.) productivity. Genetic improvement of root traits could improve nitrogen use efficiency. An association panel of 461 maize inbred lines was assayed for root growth at seedling emergence under high-nitrate (HN, 5 mmol L⁻¹) and low-nitrate (LN, 0.05 mmol L⁻¹) conditions. Twenty-one root traits and three shoot traits were measured. Under LN conditions, the root-to-shoot ratio, root dry weight, total root length, axial root length, and lateral root length on the primary root were all increased. Under LN conditions, the heritability of the plant traits ranged from 0.43 to 0.82, a range much wider than that of 0.27 to 0.55 observed under HN conditions. The panel was genotyped with 542,796 high-density single-nucleotide polymorphism (SNP) markers. Totally 328 significant SNP markers were identified using either mixed linear model (MLM) or general linear model analysis, with 34 detected by both methods. In the 100-kb intervals flanking these SNP markers, four candidate genes were identified. Under LN conditions, the protoporphyrinogen IX oxidase 2 gene was associated with total root surface area and the DELLA protein-encoding gene was associated with the length of the visible lateral root zone of the primary root. Under HN conditions, a histone deacetylase gene was associated with plant height. Under both LN and HN conditions, the gene encoding MA3 domain-containing protein was associated with the first whorl crown root number. The phenotypic and genetic information from this study may be exploited for genetic improvement of root traits aimed at increasing NUE in maize.