The impact of tillage, cowpea-maize rotation and mulching on the physicochemical properties of a Haplic Plinthosol in Ghana

The study was carried out on a Haplic Plinthosol at the Faculty of Agriculture Research station, Anwomaso in the semi-deciduous forest zone of Ghana for two years to assess the impact of tillage, crop rotation and mulching on selected soil physical, hydrophysical and chemical properties, grain and stover yields of maize and cowpea. The experiment was a split-split plot arranged in randomized complete block design (RCBD) with three replications. Tillage treatments were assigned to the main plots and consisted of conventional-no-tillage rotation (CT – NT) and continuous conventional tillage (CT – CT). In the sub plots were, cowpea-maize rotation (C – M), maize monoculture (M – M) and cowpea monoculture (C – C). Crop residue mulch that is, mulch (+R) and no mulch (-R) were assigned to the sub-sub plots. Maize and cowpea were used as test crops. The results of soil physical parameters indicated significantly (P < 0.05) lower soil bulk density and higher total porosity under the treatment interactions, conventional-no-tillage rotation x cowpea-maize rotation or maize monoculture x mulch. Soil penetration resistance increased with time and ranged between 500.1 and 1079.6 kPa with practices that included conventional-notillage rotation and mulch recording significantly (P < 0.05) lower values in both years of study. On the other hand, treatment effect on dry and wet aggregate size distribution and stability followed a consistent trend with conventional-no-tillage rotation x maize monoculture or cowpea-maize rotation x mulch recording higher fraction of large aggregates and stability than continuous conventional tillage x cowpea monoculture x no-mulch at both the 0 – 15 and 15 – 30 cm depths. Saturated hydraulic conductivity ranged between 5.40 and 16.74 cm h-1. Continuous conventional tillage x maize monoculture x mulch significantly increased saturated hydraulic conductivity than conventional-no-tillage rotation x cowpea-maize rotation x mulching. Sorptivity, vii steady state infiltrability and cumulative infiltration amount ranged between 24.7 and 167.1 mm s-1/2, 0.14 and 0.53 mm s-1, and 377 and 2823 mm respectively. These were significantly higher under conventional-no-tillage rotation x cowpea-maize rotation and mulching. Soil moisture storage increased with soil depth and was significantly higher in the 0 – 15 cm depth under continuous conventional tillage x cowpea-maize rotation x mulching. Meanwhile in the 15 – 30 cm depth, significantly higher soil moisture was noted under conventional-no-tillage rotation x cowpea-maize rotation x mulching. Soil organic carbon ranged between 1.54 – 1.86 % and 1.06 – 1.48 % respectively in the 0 – 15 and 15 – 30 cm depths. The effect of treatment interactions on soil organic carbon indicated significantly (P < 0.05) higher values under conventional-no-tillage rotation x cowpea-maize rotation x mulching at the 0 – 15 and 15 – 30 cm depths. Particulate organic carbon decreased with soil depth and was 3.71 g kg-1 (0.371 %) soil and 2.44 g kg-1 (0.244 %) soil at the 0 – 15 and 15 – 30 cm depths respectively. Water extractable organic carbon decreased with soil depth and was 13.95 mg kg-1 (0.01395 %) soil and 10.73 mg kg-1 (0.01073 %) soil at the 0 – 15 and 15 – 30 cm depths respectively. Water extractable organic carbon was significantly (P < 0.05) higher under conventional-no-tillage rotation x cowpea-maize rotation x mulch at the two depths, the former treatment interaction together with conventional-no-tillage rotation x maize monoculture x mulch and conventional-no-tillage rotation x maize monoculture x no mulch showed significantly (P < 0.05) higher impact. Mineralized carbon also decreased with soil depth and was 0.85 mg CO2 g-1 (0.085 %) and 0.54 mg CO2 g-1 (0.054 %) in the 0 – 15 and 15 – 30 cm depths respectively. It was significantly (P < 0.05) higher under continuous conventional tillage x cowpea-maize rotation x mulch, continuous conventional tillage x cowpea monoculture x mulch and continuous viii conventional tillage x cowpea monoculture x no mulch in the 0 – 15 cm soil depth. In the 15 – 30 cm depth, however, significantly (P < 0.05) higher mineralized carbon was noticed under conventional-no-tillage rotation x maize monoculture x mulch, conventional-no-tillage rotation x cowpea-maize x mulch and continuous conventional tillage x cowpea monoculture x mulch. Maize grain yield increased in the second year of the study with values ranging between 3.32 and 4.69 Mg ha-1 compared to 1.83 and 4.13 Mg ha-1 in the first year. The results showed significant differences in the impact of treatment interactions with higher values recorded under conventional-no-tillage rotation x cowpea-maize rotation x mulch and continuous conventional tillage x cowpea-maize rotation x mulch in both years of study. Cowpea grain yield ranged from 0.17 – 3.32 Mg ha-1 in 2013 and 0.61 – 2.03 Mg ha-1 in 2014 with significantly higher values recorded under conventional-no-tillage rotation x cowpea monoculture x no mulch and continuous conventional tillage x cowpea-maize x mulch in the former and latter years respectively. Conventional-no-tillage rotation in combination with cowpea-maize rotation or maize monoculture and mulch is recommended for the potential of its attributes for sustained crop production in the semi-deciduous forest zone of Ghana.

Source: KNUST