Improving effect of planosol by deep tillage combined with subsoil mixed with ameliorative materials

Abstract: Planosol is one of the main agricultural soils in the northeast of China, in which Heilongjiang and Jilin Province are relatively concentrated distribution areas. In the Heilongjiang Province, its total area is about 3.31 million hm2; the Sanjiang Plain located in its eastern region is planosol concentrated area, and its cultivated land area is about 0.88 million hm2. Planosol is a kind of regional low yield upland soil, and 3 factors namely very thin black topsoil, naturally derived hard subsoil pan and over acidification after reclamation are considered as major obstacles triggering low yield. It was found that when its silt subsoil layer and clay subsoil layer were mixed while keeping the topsoil undisturbed, good soil improvement could be obtained. Since its subsoil is short of nutrient, its poor chemical property still remains unchanged by only using subsoil mixing method. In this paper, by making plot experiment, different ameliorative materials were input into the subsoil mixed to clarify the further effect on planosol improvement. The plot experiment included 6 treatments: common subsoil loosening (CK); subsoil mixed (SML) (operated by straw subsoil mixed plough); straw + subsoil mixed (S + SML); straw + subsoil mixed + phosphorus (P) fertilizer (S + SML + P); straw + subsoil mixed + lime (S + SML + L); straw + subsoil mixed + lime + P fertilizer (S + SML + L + P). The result showed that compared with the CK treatment, the rest treatments combined with ameliorative material achieved good results not only in the aspect of subsoil physical properties, but also in the aspect of subsoil chemical properties. Soil moisture in the depth from 20 to 40 cm beneath the soil surface was increased by 2.11-6.11 percentage point. Soil hardness at the same part was reduced by 40%-50%, and its peak of soil hardness disappeared. The soil three-phase ratio was improved with solid phase reduced by 8.5-9.97 percentage point, liquid phase increased by 2.82-5.41 percentage point and air phase increased by 3.89-6.65 percentage point. Its soil bulk density was decreased by 10.13%-17.09%. In the aspect of soil chemical properties, available nitrogen (N) was increased by 82.75%-121.63%; available P was increased by 190.91%-681.82%, and especially for the treatment of adding P, available P was 6.5-6.8 times as much as the CK; available potassium (K) was increased by 20.7%-40.74%. Organic matter was increased by 157.14%-185.71%. In the aspect of alleviating soil acidity, the pH value of the treatment for adding lime was increased by 0.45-0.47. Meanwhile, soil total N, P, and K were increased. Total N was increased by 45.76%-52.54%, total P was increased by 108.14%-144.19%, and total K was increased by 8.10%-26.34%. In the year of 2016, soybean yield was increased by 13.42%-24.46%, and in the year of 2017 maize yield was increased by 13.43%-19.17%. It achieved stable effect on increasing yield by once operation. From above mentioned, the mixed subsoil combined with application of straw, lime and P fertilizer can achieve better results on planosol improvement. This study can thus provide technical support for planosol improvement, and be useful for the improvement of other soils which have similar property of low yield.