African Journal of Agricultural Research Vol. 4 (4), pp. 278-288, April 2009 Available online at http://www.academicjournals.org/AJAR ISSN 1991-637X © 2009 Academic Journals Full Length Research Paper Spatial rooting patterns of gliricidia, pigeon pea and maize intercrops and effect on profile soil N and P distribution in southern Malawi Wilkson Makumba1*, Festus K. Akinnifesi2 and Bert H. Janssen3 1Department of Agricultural Research Services, Chitedze Agricultural Research Station, P. O. Box 158, Lilongwe, Malawi. 2World Agroforestry Centre, Chitedze Agricultural Research Station, P. O. Box 30798, Lilongwe. Malawi. 3Wageningen University and Research Centre, Department of Environmental Sciences, P. O. Box 8005, 6700 EC Wageningen, The Netherlands. Accepted 27 March, 2009 The concept of competition or complementarity between tree and crop roots for below ground resources have been a major debate in simultaneous systems. Root studies were conducted in three cropping systems, namely: sole maize, pigeon pea/maize intercropping and Gliricidia sepium (Gliricidia)/maize intercropping, with the objective of understanding the potential for competition or otherwise. Pigeon pea and maize root development was monitored at 21, 42 and 63 days after planting (DAP). Also soil mineral N and Olsen P were assessed along the soil profile up to 200 cm depth. Maize roots developed faster than those of pigeon pea during the first 42 days after planting and there was little overlapping of maize and pigeon pea roots. However, the roots of both pigeon pea and maize had its peaks at 63 DAP, suggesting potential competition during reproductive growth stage of maize. In Gliricidia/maize intercropping, maize had the highest root density averaging 1.02 cm cm-3 in the top 0 -4 0 cm soil layer, whereas gliricidia had lower root length density (0.38 cm cm-3) in the top 0 - 40 cm soil layer compared to 0.65 cm cm-3 in the subsoil (40 - 100 cm). In Gliricidia/maize intercropping, mineral N was increased by 34 - 44 kg ha-1 in the 0 - 100 cm soil layer, whereas Olsen P decreased by 32 kg ha-1 in the entire 0-200 cm soil profile compared to the sole maize plot. Pigeon pea may be the “loser” in an association that involved both maize and Gliricidia. Because maize had more roots growing within 0 - 40 cm soil layer than Gliricidia it is able to take advantage of the nutrients from the applied Gliricidia prunings in the ridges. The study confirmed root compatibility between Gliricidia and maize and nutrient pumping from deep soil layers. Key words: Fertilizer trees, roots, nutrient distribution, Makoka. INTRODUCTION Competition for both the above- and below-ground re- and physiological factors controlling plant growth and sources may arise between trees and crops growing in functioning, one species may gain at the expense of the the same space and soil mass, especially when the trees other, causing one species to be a winner (strong com- have more competitive advantage than the crops petitor) and the other a loser (weak competitor) (van (Schroth, 1999). In simultaneous systems interactions Noordwijk et al., 1996). These interactions may have between component species are essentially a response competitive (deleterious), complementary (beneficial) or of one species to the environment as modified by the pre- balanced-off (neutral) overall effects. Competition occurs sence of the other (Akinnifesi et al., 1999a, 2004). De- when species have to share the resources from a limited pending on the management, and or environmental and pool. Understanding and managing competitions is cru- cial for the success and sustainability of any simulta- neous agroforestry systems (Akinnifesi et al., 2004; *Corresponding author. E-mail: [email protected]. Schroth, 1999). Makumba et al. 279 Table 1. Initial topsoil (0-20 cm) characteristics at MZ12 and MZ21, their roots growing in the deeper soil layers. It has been Makoka Agricultural Research Station, Zomba. suggested that competition between the trees and crops for belowground resources could be minimized by (1) Soil parameter MZ12 MZ21 deep ploughing so that the tree roots growing in the top Physical characteristics soil layer are sloughed off (Kowar and Radder, 1994), (2) Clay (%) 42 38 root pruning along the tree hedges (Fernandes et al., Sand (%) 46 54 1993), (3) selecting trees that have most of their roots Silt (%) 12 8 growing below the crops rooting horizon (Akinnifesi et al., Bulk density (g/cm3) 1.42 1.55 1999a), (4) shoot pruning to reduce competition for water Chemical characteristics and nutrients (Miller and Pallardy, 2001), and (5) by pH in water (1:2.5) 5.9 5.6 growing crops in ridges and trees in furrows (Akinnifesi et Organic carbon (g/kg of soil) 8.8 9.3 al, 2004). P-Olsen (mg/kg of soil) 26.0 10.3 Smallholder farmers in southern Malawi intercrop pigeon pea in Gliricidia-maize intercropping system. Exchangeable K (mmol (+)/kg of soil) 3.0 3.7 Trees are grown in furrows and maize and pigeon pea on Exchangeable Ca (mmol (+)/kg of soil) 44.0 17.3 ridges. This practice further increases the harmony of Exchangeable Mg (mmol (+)/kg of soil) 16.0 4.2 intercropping tree and crops in a small piece of land. The information previously obtained from wider alleys (4 - 5 m) (Akinnifesi et al., 1995, 1999 b, c; Itimu et al., 1997) may not easily be extrapolated to Gliricidia intercropping system in Malawi with 1.5 m between rows. Since root Knowledge of root stratification of the trees/shrubs and characteristics of trees change with crop husbandry, tree the associated crops in an agroforestry system is needed management and site conditions (Akinnifesi et al., 1995, in order to ascertain the extent of competition or comple- 1999b, 2004; Schroth, 1999; van Noordwijk et al., 1991, mentarity or otherwise between the trees and the crops. 1996), it is essential to understand the rooting patterns of Previous root studies have revealed that trees having trees and crops in a simultaneous intercropping of Gliri- large and extensive roots will interfere with seedbed pre- cidia with maize and pigeon pea. paration or tillage operations (Akinnifesi et al., 2004). The premise of the study was that the simultaneous Tree species with lateral roots confined to less than 1 m intercropping agroforestry systems as practiced in Malawi distance from the tree trunk, are more desirable in will face competition for belowground resources, but that simultaneous agroforestry systems that require tillage of the practice of growing trees in furrows and crops on the inter-row spaces (Akinnifesi et al., 1999a, b; Ruhigwa ridges minimizes such competition. We further hypothe- et al., 1992). Shallow rooted tree species that exhibit size that rooting systems of Gliricidia are compatible with rapid decline in root mass, length or density with maize and pigeon pea in the intercropping system. This increasing soil depth may compete highly with crops on study was undertaken to (1) understand the vertical and soil nutrient resources, whereas trees with high con- horizontal root distribution of Gliricidia, pigeon pea and centration of their fine roots in the topsoil but at the same maize in a simultaneous system, (2) increase our under- time with a substantial proportion of their fine roots in the standing of pigeon pea and maize root development dur- deeper soil layers may compete less (Akinnifesi et al., ing the growing period in an intercropping system, and (3) 2004; Schroth, 1999; Schroth and Zech, 1995;) because understand the effect of Gliricidia and pigeon pea on they explore a large volume of soil. Tree roots at soil mineral N and Olsen P down the soil profile. depths below the feeding zone of most annual crops may capture nutrients from deeper resources and transfer them to the surface (Van Noordwijk et al., 1996). MATERIALS AND METHODS The success of the simultaneous intercropping of trees The studies were conducted in two separate fields of about 300 me- with crops in agroforestry system is dependent on the ters apart, that is, the MZ 12 and MZ 21, both at Makoka Agricu- temporal and spatial complementarity of resource capture ltural Research Station during 2000-01 and 2001-02 seasons. The by trees and crops (Akinnifesi et al., 2004; Cannell et al., at MZ12 trial was established in December 1991 for studying long- 1996). In simultaneous agroforestry systems, pruning term biophysical performance of Gliricidia intercropping system including nitrogen dynamics (Ikerra et al., 1999), P dynamics management of the aboveground part of the trees (Mweta et al., 2007), maize yield and tree biomass production reduces both the aboveground as well as below ground trends (Akinnifesi et al., 2006), and C sequestration (Makumba et competition (Akinnifesi et al., 1995). al., 2007). The MZ21 was established in December 1995 for under- Competition for belowground resources is high when standing the intercropping of Gliricidia intercropping and Cajanus the agroforestry trees have most of the fine roots con- cajan (pigeon pea) (Chirwa et al., 2006). The profile soil charac- fined in the same strata as the associated food crop teristics of both sites are presented in Table 1. The experiment is a randomized complete block design with three blocks. Each treat- (Akinnifesi et al., 1999a; Ruhigwa et al., 1992; Schroth, ment was replicated thrice. For the purpose of this study, the fol- 1995, 1999), and low when the trees have few roots lowing six treatments were selected: (1) Monoculture maize without growing in the rooting horizon of the crops and more of N-fertilizer (Control), (2) Monoculture maize with 50% of the recom- 280 Afr. J. Agric. Res. Tree row Maize rows Tree row Gliricidia Maize Pigeon pea Grid frame Figure 1. a) Spatial arrangement of trees and crops in the Gliricidia/maize intercropping system at Makoka; b) Mapping of roots at MZ21 in a Gliricidia-maize-pigeon pea intercropping system (Root trenches were dug parallel to the ridges and tree rows in each plot).