Vertical root distribution in single‐crop and intercropping agricultural systems in Central Kenya

Abstract

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 using the trench wall profile method in single-crop systems of maize (Zea mays L.) and in intercropping systems of maize and legumes (common bean, Phaseolus vulgaris L.; 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 vertical 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) of the soil profiles (Y = 1 -b d ). 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.

Loss of deep roots limits biogenic agents of soil development that are only partially restored by decades of forest regeneration

“…The great depths to which tree roots extend Jackson et al, 1996;Maeght et al, 2013;Freycon et al, 2014;Fan (Acuna and Wade, 2013;Ahmadi et al, 2011;Gan et al, 2011;Neykova et al, 2011;Trachsel et al, 2013), and the centennial timescale over which forest roots continue to expand (Zangaro et al, 2008;Knops and Bradley, 2009;Devine et al, 2011;Yuan & Chen, 2012;Sun et al, 2015) are widely observed phenomena. However, to our knowledge the current study is the first to quantify root densities to such depths in replicated plots representing distinct disturbance histories, and to determine a meaningful influence of forest age on rooting depth distributions.…”

Variability of physical attributes in tropical weathered soil cultivated with irrigated beans (Phaseolus vulgaris L.)

“…Long-term soil degradation is reported with a greater intensity on the soil surface with the formation of compacted layers and superficial sealing. This effect might facilitate the erosion process, causing a decrease of essential soil functions, mainly those linked to structure stability, aggregated fractioning, density increase, microporosity (Mi) increase, and aeration porosity decrease, influencing root growth and, consequently, affecting yield (Neykova et al, 2011). Irrigation systems such as a central pivot cover large areas.…”

Interspecies Interactions in Relation to Root Distribution Across the Rooting Profile in Wheat-Maize Intercropping Under Different Plant Densities

“…Yield advantage is typically related to root growth and development (Xu et al, 2010; Wan et al, 2013), root distribution patterns across the rooting profile (Liu et al, 2015), and spatial variability in root traits. The root distribution patterns at the different soil depths vary with many factors, such as the morphological and physiological traits of the crops (Liu et al, 2010; Neykova et al, 2011), soil moisture (Smucker and Aiken, 1992) and nutrient contents, and plant density (Prasad and Brook, 2005). However, little information on the root characteristics of wheat-maize intercropping at different plant densities is available in the scientific literature.…”

“…Under dryland conditions, improving root distribution across the soil profile can enhance the crop water use efficiency (Wang et al, 2012) and thereby increasing crop productivity (Drew et al, 1973). Intercropping of crops with contrasting growth habits can improve primary resource use in both spatial and temporal contexts due to improved root distribution and connection between the species (Neykova et al, 2011). In many cases, the positive change in the soil environment brought about by one intercrop favors the growth of the other intercrop (Li et al, 2006).…”