Mechanisms And Mechanical Approaches Of Root-zone Management For Efficient Nutrient Use In Intensive Cropping System For Maize

Root system is essential for plants to acquire resources from the soil. The optimal root architecture and distribution in soil layers can improve nutrients and water use efficiency. It is great significance to take a deep understanding of the mechanisms of nutrient acquisition by roots and make the reasonable adjustment for realizing high yield and high nutrient use efficiency. We hypothesized that the target for high yield and high nitrogen use efficiency (NUE) can be achieved through properly manipulating root morphological and physiological traits as well as intensifying rhizosphere chemical processes and promoting root distribution under field conditions, which is critical for sustainable crop production. In the present study, two-year field experiments were conducted to test root morphological responses to soil penetrometer resistance and localized nutrient supply, which demonstrated the mechanisms of soil compaction restrictions on root and shoot growth of maize. By using a novel simulation method under field conditions, we determined the relationship between deep root and yield, and quantified the contribution of deep root to maize yield. Two-year field experiments were conducted to study the effects of soil cultivation and nutrient application patterns on root development, root distribution and maize growth. Based on this, the strategy of root management for efficient nutrient use in the intensive cropping system was developed and tested in the field experiment. Finally, we explored the mechanical approaches with the strategy of root management for efficient nutrient use in the intensive cropping system, which can be used to solve problems of agricultural labor shortage by coordinating integration of agricultural machinery and agronomic technology. Key points of the results and progress were summarized as follows:(1) Root growth was impeded to subsoil by the strongly-compacted layer (plow pan) in the soil, resulting in a decreasing shoot biomass. When the soil bulk density of the plow pan was greater than 1.55 g cm-3, root growth was largely restricted in the 0-20 cm soil layer, with a greater horizontal spread of roots in the top soil layer. The compacted layer impeded root growth to the deep soil, which made plant roots, soil nutrients and moisture not match in temporal and spatial, causing plant biomass decreased.(2) Deep roots were essential for maize growth and high yield. There was a linear-with-plateau model between the response of grain yield and the increased proportion of deep root (% of the root distributed in the 20-60/0-60 cm depth). The minimum proportion of deep root for achieving the maximum yield was 3.3% of root dry weight. When the proportion of deep root (20-60 cm depth) was over the critical value, the maize yield was stable at high level, which demonstrated that there was less positive effect of deep root to maize yield with increasing proportion of deep root.(3) Localized supply of ammonium sulphate plus superphosphate (ASP) significantly increased early root proliferation in the nutrient-rich zone compared with broadcast fertilizer application. Deep plowing integrated with localized application of ASP significantly improved maize root growth (both horizontally and vertically) and grain yield. Localized nutrient supply stimulating shallow root proliferation could be integrated with deep plowing to facilitate deep root distribution, which was an effective approach to improve maize yield and NUE in intensive production systems.(4) The relationship between deep root distribution and deep loosening area was established, which provided a theoretical basis for optimizing soil cultivation. Optimal deep plowing (deep loosening) integrated with localized application of ASP significantly improved maize root growth (both horizontally and vertically) and grain yield (10.7-19.5%).(5) By adjusting the parameters of agricultural machinery and optimizing agronomic techniques, we improved the integrated technology of mechanical sowing combined with mechanical fertilization technology at the later growth stage of maize. High yield and high NUE could be achieved simultaneously in the intensive cropping system through implementing the technology of agricultural machinery combined with agronomic approaches and the large-scale land operation. Comparing with farmers’practices, crop yield and PFPN increased by 10-20% and 15-25%, respectively. The work efficiency was improved, as well as the agricultural labor force was significantly saved.The match of roots with soil nutrients and water in spatially and temporally is critical for plants to acquire efficiently soil resources, and it is regarded as a key point to realize high yield and environment protection simultaneously in intensive farming system. By studying root response morphologically to soil mechanical resistance and heterogeneous nutrient, the mechanisms of soil compaction on restricting root distribution and shoot growth, and the contribution of deep root to maize yield were revealed. By integrating deep loosening combining with localized application of nutrients, maize yield and NUE were improved due to deep root penetration and shallow lateral root proliferation. The combination of agricultural machinery with agronomy and field validation demonstrated the potential and effectiveness of the mechanical approaches of root-zone management on saving labor force and increasing NUE and yield.