The Effect Of Topsoil Depth And Bulk Density On Soybean Growth And Yield

Soybean is an important grain and oil crops, occupies a very important position in the national economy. Tillage can adjust topsoil structure which soybean could grow in an suitable environment of the soil. Deep plowing can reduce soil bulk density and increase topsoil depth, but depth is too great not only for farming farm machinery requirements increase and unnecessary waste. Therefore, The study of most suitable topsoil depth and bulk density indicators for growth of soybean so that so that the soybean crop could reach the maximum is practical significance.The experiment was conducted in 2013-2014. The cultivars is Heinong 66 which planted using soil box method. Set plow layer thickness of 5cm and the bulk density is 1.60 g / cm3, 10 cm, 15 cm, 20 cm, 25 cm, 30 cm, 35 cm and no plow as seven different topsoil depth treatment. Soybean plants by measuring dry matter accumulation, and accumulation of nutrient contents in R1, R5 and R8 to study the effects of the topsoil depth on soybean growth. Then by setting plow layer thickness of 5cm and the bulk density is 1.60 g / cm3, 1.00g/cm3,1.15g/cm3,1.30g/cm3 and 1.45g/cm3 four bult density topsoil treatment and measure the dry matter accumulation, and the accumulation of nutrient contents amount of soybean in R1, R5 and R8 to study the effects of the bult density on soybean growth. Also through the indoor and outdoor experimental simulation study alternating wet and freezing and thawing effect on soil bulk density and plow impact. The results showed that:There is a significant impact on the topsoil depth to the dry weight P, K content and accumulation of soybean in each period. The deeper topsoil depth soybean dry weight accumulation, NPK content and accumulation will be higher. Typically early soybeans grown in soil plow the indicators to be significantly higher than the growth in the plow layer soil. As soybean grown to full maturity, the deeper topsoil treatment in accumulation of dry matter and nutrient accumulation is not significant to the no plow treatment. In addition, there is a positive correlation between topsoil depth and yield, yield of the topsoil depth above 25 ~ 30 cm is the highest, on this basis, add topsoil depth has little effect on soybean yield.Soil bulk density of soybean dry weight, P, K content and accumulation will also have a significant impact. Soybean dry weight, P, K content and accumulation increases with the density of the soil first and then increase the downward trend. Between soil bulk density 1.00g/cm3,1.15 g/cm3 and 1.30g/cm3 treatment was not significant, but significantly higher than the bulk density of 1.45 g / cm3. When the soil bulk density reaches 1.30 g / cm3, the highest index of soybean yield components, but the influence of soil bulk density for soybean seed kernel weight is not significant.A certain impact between the bulk density and soil freezing and thawing. Generally makes smaller bult density increased soil compaction, leaving the compaction of soil bulk density through the large decline. Bulk density of 1.15g/cm3 treatment and soil 1.30g/cm3 treatment increased by 6.09% and 2.31%, respectively; bulk density of 1.45g/cm3 treatment and soil 1.60g/cm3 of bulk density decreased after thawing 2.07% and 3.13% respectively. Generally, the influence of soil freezing and thawing will more obvious when soil bulk density is larger or smaller.After wetting and drying cycles soil bulk density will decrease, the largest decline of the bulk density was the first wetting and drying cycles. When the number of wetting and drying cycles reaches four, then add the wetting and drying cycles have little effect on soil bulk density. When the initial soil bulk density reached 1.50g/cm3, alternating wet and dry bulk density and the number of linear equations for y = 1.495(x+1)-0.07 R2 = 0.987. Under natural precipitation alternating wet and dry conditions that affect soil bulk density and indoor simulation similar to the larger soil bulk density with alternating wet and will decline, while the smaller soil bulk density of soil bulk density will rise. When the soil bulk density reached 1.30 g / cm3, the bulk density will rain with wetting and drying cycles naturally be a slight increase, but the magnitude of the rise is not obvious.The plough density will be as the change of soybean growth process and produce a certain. The plough layer density of 1.15g/cm3 will gradually increase, 1.45g/cm3 and 1.60g/cm3 plough layer density will increase obviously, and the plough layer density changes very little when the bulk density 1.30g/cm3. Shows that when the soybean growth to late, soil bulk density differences between bulk density of the plough will decrease obviously.