Vertical root distribution in single-crop and intercropping agricultural systems in Central Kenya
Obando, Joy Apiyo
Thomas, F. M.
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Intercropping is an important and widespread land-management system in the tropics. At two agricultural sites in Central Kenya differing in elevation and soil type Haplic Nitisols (eutric) and Vitric Gleysols (eutric, epiclayic, endoclayic), we investigated the vertical root distributions usingthe trench wall profile method in single-crop systems of maize (Zea maysL.) and in intercrop-ping systems of maize and legumes (common bean, Phaseolus vulgarisL.; pigeon pea, Cajanus cajan[L.] Millsp.) to test for possible differences in the use of water and nutrient resources. The physico-chemical soil properties of the sites were similar and imposed no restrictions to the verti-cal growth of the roots into soil depths of 1.4 m. The vertical distributions of the fine roots∅0.5–2 mm) and very fine roots (∅<0.5 mm) were quantified by calculating the parameter b which was computed from the cumulative fraction ( Y) of the root densities along the depth (d)ofthe soil profiles (Y=1–bd). We found no consistent differences between the single-crop and the intercropping systems in the rooting depth down to 1.4 m. However, higher B values for fine roots of the intercropping systems were indicative of a more homogeneous vertical root distribution than in the single-crop fields. In the intercropping fields, 50% of the total number of fine roots were distributed over the uppermost 36 cm of the soil, whereas in the single-crop fields, 50% of the fine roots were concentrated in the uppermost 15–21 cm. Medium-sized roots (∅> 2–5 mm) were detected in the intercropping fields only. The more homogeneous root distribution in the intercropping fields likely indicates a more efficient use of the limited resources nutrients and water. Keywords: cumulative root distribution / Mount Kenya / resource utilization / Zea mays / Phaseolus vulgaris / Cajanus caja