Straw Mulching with Minimum Tillage Is the Best Method Suitable for Straw Application under Mechanical Grain Harvesting

Mechanical grain harvesting is a crop production development direction. However, the residue management methods suitable for mechanical grain harvesting have been not established. In order to study the effect of residue management modes on maize yield formation and explore the best residue management methods for mechanical grain harvesting, four crop field surveys were carried out in Southwest China. Crops were mechanically harvested, and the residues were shredded and returned to the field using various straw application methods including straw deep burial with plowing (SDBP), straw shallow burial with rotary tillage (SSBRT), and straw mulching with minimum tillage (SMMT). The first-season rape residues were returned to the field, and the second-season maize yield under SDBP and SSBRT was significantly higher than that under SMMT. However, with the increase in rounds of residue application, compared with SDBP and SSBRT, SMMT continuously increased the soil moisture content in the 0–30 cm soil layer at the early stage of maize growth, increased the soil alkaline-hydrolyzed nitrogen content in the 0–20 cm and 40–60 cm layers, and reduced the soil compaction under 40 cm layer, which were more conducive to the root system growth. Maize yield with the SMMT increased by 5.4% compared with that of the previous season, while the yields with SDBP and SSBRT decreased by 16.7% and 12.7%, respectively, compared with those of the previous season. In conclusion, it is recommended to employ the SMMT method during crop mechanical harvesting, which is of great significance to improve soil quality and increase maize grain yield.

Efficiency of Reductive Soil Disinfestation Affected by Soil Water Content and Organic Amendment Rate

Reductive Soil Disinfestation (RSD) is a good method which can restore degraded greenhouse soil and effectively inactivate soil-borne pathogens. However, the approach needs to be optimized in order to facilitate its practical application in various regions. In the present work, we investigated the effect of soil water content (60% water holding capacity (WHC), 100% WHC and continuous flooding) and maize straw application rates (0, 5, 10, and 20 g kg−1 soil) on the improvement of soil properties and suppression of soil-borne pathogens (Fusarium oxysporum, Pythium and Phytophthora). The results showed that increasing the soil water content and maize straw application rate accelerated the removal of excess sulfate and nitrate in the soil and elevated the soil pH. Elevating the water content and maize straw application rate also produced much more organic acids, which could strongly inhibit soil-borne pathogens. Soil properties were improved significantly after RSD treatment with a maize straw amendment rate of more than 5 g kg−1, regardless of the water content. However, RSD treatments with 60% WHC could not effectively inactivate soil-borne pathogens and even stimulated their growth by increasing the maize application rate. RSD treatments of both 100% WHC and continuous flooding could inactivate soil-borne pathogens and increase the pathogens mortality indicated by cultural cells relatively effectively. The inhibited pathogens were significantly increased with the increasing maize application rate from 5 g kg−1 to 10 g kg−1, but were not further increased from 10 g kg−1 to 20 g kg−1. A further increased mortality of F. oxysporum, indicated by gene copies, was also observed when the soil water content and maize straw application rate were increased. Therefore, RSD treatment with 60% WHC could improve soil properties significantly, whereas irrigation with 100% WHC or continuous flooding was a necessity for effective soil-borne pathogens suppression. Holding 100% WHC and applicating maize straw at 10 g kg−1 soil were optimum conditions for RSD field operation to restore degraded greenhouse soil.