Winter rotational cover crops (WRCC) are often used to boost soil fertility and plant nutrition. However, selection and use of WRCC for soil physical improvement is usually overlooked. The objective of this study was to determine the effects of WRCC on soil strength, aggregate stability and water conservation of a hardsetting soil. The soil physical properties were determined after four rotations of growing monocultures of vetch (Vicia dasycarpa cv. Max), lupin (Lupinus angustifolius cv. Tanjil) and oats (Avena sativa cv. Sederberg) and after two rotations of growing bicultures of oats (Avena sativa cv. Pallinup) and vetch (Vicia dasycarpa cv. Max) across two soil layers, 0 to 15 cm and 15 to 30 cm. The individual WRCC and a weedy fallow constituted the treatments in the monoculture study whilst in the biculture study the various combinations of WRCC namely; 90% oat plus 10% vetch (O90V10); 70% oat plus 30% vetch (O70V30) and 50% oat plus 50% vetch (O50V50) and a weedy fallow constituted the treatments. After four rotations with cover crop monocultures, oats significantly (P ≤ 0.05) reduced penetration resistance (PR) whilst vetch increased PR in both soil layers compared to the weedy fallow control. The effect of the biculture treatments was only experienced within the 15 to 30 cm depth. The treatments O50V50 and O70V30 increased the PR compared to the control. The WRCC in monoculture significantly increased the soil aggregate stability relative to the control in both soil layers. Vetch, lupin and oats resulted in a 41.7%; 20.4% and 15.7% increase in MWD in the 0 to 15 cm soil layer and 47.2%; 44.2% and 39.7% in the 15 to 30 cm depth, respectively. An increase in aggregate stability was associated with increased macro-aggregation. Under the biculture, WRCC slightly increased, non- significantly, the aggregate stability. Both hot water and dilute acid extractable polysaccharides showed no significant correlation with aggregate stability in the two studies. Oats monoculture resulted in a significant difference (P ≤ 0.05) on cumulative infiltration compared to the control. However, after 2 h vetch and lupin showed no significant difference from the control on cumulative infiltration. Oats resulted in a 7.8% increase in final infiltration rate (FIR) whilst vetch and lupin reduced FIR by 9% and 16.7% respectively, compared to the control. Bicultures of oats and vetch significantly (P ≤ 0.05) increased cumulative infiltration compared to the weedy fallow control. A similar significant increase in FIR was also observed under bicultures. The treatments O50V50; O90V10 and O70V30 resulted in a 163.3%; 113.3% and 105.4% increase in FIR respectively, compared to the control. Cover crop monocultures significantly (P ≤ 0.05) increased plant available water (PAW) compared to the weedy fallow, with vetch, oats and lupin resulting in a 28.3%; 22% and 23.9% increase respectively, in PAW. However, no significant differences were observed on PAW after two rotations with bicultures. Compared with winter weedy fallow, WRCC improved most of the soil physical properties under study, with the most suitable results expected under bicultures compared to monocultures. Under CA, selection of WRCC like oats, vetch and lupin, one should therefore take into consideration their effects on soil physical properties as a selection criterion and not biomass and fertility alone.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufh/vital:11868 |
| Date | January 2012 |
| Creators | Mupambwa, Hupenyu Allan |
| Publisher | University of Fort Hare, Faculty of Science & Agriculture |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis, Masters, MSc Agric (Crop Science) |
| Format | xv, 91 leaves; 30 cm, pdf |
| Rights | University of Fort Hare |
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