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Soil penetration resistance (SPR) is one of the major indicators of soil physical properties. Crop residue managements, tillage practices and their interactions exert significant effects on the SPR. However, rare information is available in the sloping farmland of Mollisols. Field experiments were conducted to investigate the variations of the SPR as affected by crop residue managements and tillage practices on the sloping land in Northeast China from 2015 to 2019. The split-plot experiment was arranged with two crop residue managements (removed, REM and retained, RET), and three tillage practices (no tillage, NT; rotary tillage, RT; plow tillage, PT). SPR data in 0-80 cm soil depth was measured at the end of harvest of maize monoculture. Results showed that the two crop residue managements induced significant variations in the SPR at 0-15 cm, 15-30 cm and 0-80 cm soil depths under NT, RT, and PT treatments, respectively. In comparison with RET treatment, the average values of the SPR under REM treatment were 10.9% and 8.9% higher in 45-60 cm and 60-80 cm soil depths, respectively. The average values of the SPR under PT treatment were 12.4% and 14.1% lower in 0-15 cm soil depth, and 23.9% and 10.4% lower in 15-30 cm soil depth than those under NT and RT treatments. However, the average value of the SPR under PT treatment was 11.2% and 22.0% higher in 60-80 cm soil depth than those under NT and RT treatments, respectively. The SPR generally decreased with the slope position declined in the deeper soil depth (except for the NT+RET treatment). The findings from this research can provide a scientific reference for the establishment of rational cultivation and the sustainable development of productivity on the sloping land of Mollisols in cold regions. [ABSTRACT FROM AUTHOR]

Appropriate mechanized straw returning and tillage sowing techniques were effective means to optimize soil physical properties and enhance agricultural productivity, as well as important measures for the conservation and restoration of mollisols region in Northeast China. Under the condition of full-scale maize straw returning, four mechanized tillage and sowing modes were set, including plough tillage and sowing (PTS), combined tillage and sowing (CTS), no-tillage and sowing (NTS), and no-tillage and sowing with straw mulching (NTSM). In 2020 and 2021, the study investigated the effects of different mechanized tillage and sowing modes on soil physical properties, soybean yield and economic benefits. The results showed that during the pod-setting and pod-filling period of soybean, the NTS and NTSM treatments exhibited better effects on deep soil insulation and shallow soil moisture retention, the soil physical structure of PTS and CTS treatments were relatively ideal. Compared with PTS and CTS treatments, NTS and NTSM treatments significantly increased soil gravimetric water content (SWC) by 2.35% to 7.98% in the 5-15 cm soil layer and increased soil temperature (ST) by 3.94% to 10.42% in the 2535 cm soil layer (p<0.05), significantly increased soil bulk density (SBD) by 2.98% to 6.72% and significantly reduced soil total porosity (STP) by 3.88% to 6.53% in the 5-25 cm soil layer, and significantly reduced soil gas phase ratio by 8.26% to 6.27% at the 15-25 cm soil layers, which caused soil three-phase ratio (STPR) of PTS and CTS treatment in 15-25 cm soil layer were relatively ideal. The soybean yield of NTSM treatment in 2020 was not significantly different from PTS and CTS treatment (p>0.05), the soybean yield of NTSM treatment in 2021 significantly increased by 7.30% and 5.84% over PTS and CTS treatments, respectively. And the average annual profit per unit area of NTSM treatment increased by 12.84%, 12.41% and 8.57% compared with PTS, CTS and NTS treatments, respectively. Therefore, it was recommended to combine NTSM technique with PTS or CTS technique in a maize-soybean rotation system in mollisols region. The research results provided reference for the selection of appropriate mechanized tillage and sowing techniques in Northeast China's mollisols region and had important guiding significance and practical value for the construction of rational plow layers and the implementation of conservation tillage. [ABSTRACT FROM AUTHOR]