Impact of different levels of soil compaction and soil amendments on the growth and yield of maize and soybean

Two factorial pot experiments arranged in a Completely Randomised Design (CRD) with three replications were carried out to assess the impact of different levels of soil compaction and soil amendments on root growth and biomass yield of maize (Zea mays L.) and soybean (Glycine max L.). The treatments were soil compactions (bulk densities as proxy) of 1.3, 1.5 and 1.7 Mg m-3 and soil amendments of control (no soil amendments), poultry manure, NPK fertilizer and ½ rate each of PM and NPK fertilizer. The soybean and maize were grown in plastic buckets filled with the test soil (Ferric Acrisol). At the bulk density of 1.7 Mg m-3, aeration porosity was reduced below the critical level of 10 % favourable for gaseous exchange. Soil compaction reduced plant height of maize and soybean. Increasing soil compaction resulted in the accumulation of most of the root biomass in the uncompacted soil above the compacted layer. Addition of soil amendments increased the relative root biomass of maize in the uncompacted soil while that in the compacted soil was reduced. In the case of soybean, although the relative root biomass in the uncompacted soil was relatively greater than that of maize, application of soil amendments tended to slightly decrease the relative root biomass over that of the Control. High soil compaction induced more root growth in the uncompacted soil and periphery of the soil core than the compacted zone. The applied soil amendments significantly increased the RPR of both crops in relation to the control. The shoot biomass of both crops decreased with increasing soil bulk density. All the applied soil amendments significantly increased the shoot biomass of maize and soybean over the Control. The magnitude response of the crops to the soil amendments was greater in soybean than in maize. Soil compaction and amendments significantly influenced root: shoot ratio of both crops. At the bulk density 1.3 to 1.5 Mg m-3, the root: shoot ratio decreased with increasing iii compaction. Beyond the bulk density of 1.5 to 1.7 Mg m-3, the root: shoot ratio increased with increasing soil compaction. The soil amendments applied significantly influenced the root: shoot ratio of maize but not soybean. The soil amendments increased the biomass of both root and shoot but more so in the former than the later. The amendment x compaction interaction showed that the root: shoot ratio was influenced by the type of crop (cereal legume) and the confounding effects of factor interactions on the relative increases/reduction in shoot and root growth. The uptake of N, P and K by maize and soybean decreased with increasing bulk density in the order of 1.3> 1.5> 1.7 Mg m-3. The adverse soil conditions created by increasing soil compaction accounted for the reduction in mineral uptake. Apart from the potassium, application of the soil amendments increased the nutrient uptake of the crops. Soil compaction accounted for 52 to 100 % of the variations in the magnitude of the measured parameters of maize and 62 to 98 % were for soybean while soil porosity accounted for 78 to 97 % of the variation in maize and 50 to 86 % to variations observed in soybean. The ideal bulk density for shoot biomass production of both crops should be within the range of 1.3 to < 1.5 Mg m-3. At soil bulk density of 1.5 Mg m-3 and above, soil amendment should be added to ameliorate the negative impact of soil compaction.

Source: KNUST