Effects of mechanical compaction on soil physical properties, maize growth and yield in farmland

【Objective】The effect of large-scale agricultural machinery compaction on soil physical characteristics, and the growth and yield of maize in practical production was studied to provide the basis for improving tillage measures, achieving strong roots and high yields of crops and sustainable production of soil.【Method】Recompacted plot(JS) by grain combine harvester and conventional harvest without recompacted plot(CK) at wheat harvest time were selected in wheat-corn double cropping system, and using maize varieties Denghai 605(DH605) and Denghai 3(DH3) as materials, bulk density and water content of soil before maize sowing and agronomic traits, photosynthetic characteristics, dry matter accumulation and distribution, ear traits and yield of maize were measured.【Result】The soil bulk density and water content in the 0-50 cm soil layer of JS treatment were both higher than that of CK, and the soil bulk density of 0-10 and 10-20 cm soil layers were significantly higher than that of CK(P<0.05, the same below). That was to say, the effect of repeated compaction by large agricultural machinery on the soil bulk density was mainly concentrated in the 0-20 cm arable layer. Arable layer soil compaction resulted in the decrease of maize root number and root dry weight, the developmental dysplasia of root and overground parts, blocked stem and leaf differentiation, and the decrease of leaves number and internodes per plant, the decline ofleaf area index, plant height, photosynthetic rate, dry matter accumulation, the decrease of grains number per ear and 100-grain weight, ultimately led to more than 20% reduction in yield. Compared with two cultivars, the root growth of DH3 was greatly affected by compaction stress. Compared with CK, the root layer number, root number, root dry weight and root-top ratio of DH3 under JS treatment were significantly reduced by 17.9%, 26.9%, 45.2% and 32.9%, respectively, while DH605 were decreased by 0, 14.4%, 31.7% and 12.7%, respectively, and only the root dry weight was significantly different. Compared with CK, leaf area index and SPAD of ear leaf of DH605 were significantly decreased by 36.9% and 14.4%, respectively, ear coefficient was significantly increased, stem diameter and 100-grain weight were significantly decreased under JS treatment. Although DH3 root growth were greatly influenced by compaction stress, leaf area index of DH3 was 21.8% lower than CK, and the SPAD of ear leaf, ear coefficient, stem diameter, 100-grain weight of DH3 under JS treatment were not significantly different with CK(P>0.05), and the proportion of dry matter allocated to leaves, and grains increased than CK under JS treatment. Eventually, the yield reduction(20.8%) was not greatly different with DH605(24.4%). 【Conclusion】The phenomenon of surface soil compaction caused by repeated rolling of large farm machines in current production has been very serious, which inhibits the growth of no-tillage direct seeding maize and significantly reduced the yield. Different maize varieties have different responses to soil compaction stress. In production, the adverse effects of soil compaction on crop growth can be reduced by deep loosening(ploughing), straw returning to the field, and selection of soil compaction resistant varieties.