Banana leaf pruning to facilitate annual legume intercropping as an intensification strategy in the East African highlands
Introduction
Banana-legume intercropping is important in several countries of the African Great Lakes region (AGLR) including Uganda, Rwanda, Burundi, Democratic Republic of Congo (DR Congo) and north-western Tanzania (Wortmann and Sengooba, 1993; Nzawele et al., 2009; Ntamwira et al., 2013a, b; 2014). Banana-legume intercropping is widely practiced due to high population pressure on the land. The region is characterized by high population densities estimated at between 300 and 350 inhabitants per km2 (DSRP, 2005; CIALCA, 2010), with each household typically living on less than 0.5 ha of land. The incorporation of food and/or fodder legumes into banana cropping systems in AGLR could increase the use efficiency of land (Sileshi et al., 2007) and other resources in smallholder banana farms (Ouma, 2009). It is aimed at maximizing productivity and minimizing risks related to, for example, climate change, pests and diseases (Nyabyenda, 2006; Dapaah et al., 2003; Zinsou et al., 2004) and helps in suppression of weeds (Amanullah et al., 2007). Furthermore, intercropping with nitrogen-fixing legumes may also be a strategy to offset the depletion of soil nitrogen (Chakeredza et al., 2007), thereby contributing to increasing productivity of the system. For example, intercropping with grain legumes (common beans, cowpea, groundnut, pigeon pea or soybean) has been reported to increase productivity with land equivalent ratios of 1.2–1.9 (Pypers et al., 2010).
Wortmann and Sengooba (1993) compared the performance of 16 non-climbing bean genotypes intercropped with East African highland banana with that in their respective sole crop systems. Intercropping reduced the bean yields to only 50% of the sole bean yields yet the intercrop bean density was 68% of the sole crop. This incongruous response to reduction in the bean density in the intercrop compared with that in the sole crop suggests that the banana-bean intercrops were affected by competition for light, water and nutrients, which if well understood can guide the optimization of the system for productivity. Below ground competition for moisture and nutrients in the banana-bean intercrop probably limits bean productivity since both banana and bean species are shallow-rooted (Wortmann and Sengooba, 1993) and require large amounts of nitrogen (N), phosphorus (P) and potassium (K) for growth and development (Maria et al., 2002; Ganeshamurthy et al., 2011; Marschner, 2011; McGrath et al., 2013). Above ground shading of the shorter legume plants by the banana canopy could reduce light interception, growth and yield of the legumes (Nyambo et al., 1982; Davis et al., 1987). Consequently, farmers e.g. in eastern Democratic Republic of Congo, often prune banana leaves to enhance sunlight penetration to the understory component crop so as to improve their growth and yield (Mirindi, 2011; Ntamwira et al., 2013a, b; 2014; Ocimati et al., 2013; Blomme et al., 2017). However, leaf pruning perpetuates the spread of the bacterial wilt disease of banana (Blomme et al., 2017) and is potentially detrimental to the banana yield (Robinson et al., 1992), hence the need to analyze the leaf pruning effects in banana-legume intercrop systems.
Ntamwira et al. (2013a; 2014) observed no significant differences in banana yield when leaves of fully-grown plants were reduced to seven on farmers’ fields and five in controlled field experiments compared with non-pruned controls over four annual cropping seasons. In these experiments, leaves were only cut once when plants were at the flowering stage. In contrast, significant declines in banana plant crop growth and yield were observed when leaves were reduced to four or 7 leaves starting from the third month of planting in controlled field experiments (Ntamwira et al., 2013b). The different legume species (soybeans, bush and climbing beans) performed better when banana leaves were pruned across the three experiments. The Ntamwira et al. (2013b) study reported findings of two bean cropping seasons and the banana plant crop (i.e. first crop established from plantlets or suckers) planted at a spacing of 2 m x 2 m. Our work builds on Ntamwira et al. (2013b) taking into account the significantly higher growth vigor and canopy cover of the banana ratoon crops (new shoots in a banana stool retained for the following crops) compared to those of the plant crop (e.g. Robinson et al., 1993). This study analyzed the interaction of the annual crops with the banana crop under different pruning levels over a three years period (i.e. two banana cropping seasons). Higher shade and competition levels were anticipated in additional season compared to those observed by Ntamwira et al. (2013b).
The specific objective of this study was to determine the requisite banana leaf pruning intensity to optimize productivity of the intercrops. It was hypothesized that there is no effect of banana leaf pruning intensity on the overall land use efficiency and net returns from banana-legume intercropping regardless of banana crop cycle and component legume species. The findings of this study could be relevant for guiding farmers’ decisions on banana intercropping and leaf pruning practices.
Section snippets
Study location description
This study was conducted at the Institut National d’Etudes et Recherches Agronomiques (INERA), Mulungu research station in the South Kivu Province in eastern Democratic Republic of Congo. Banana is an important food and cash crop in eastern DR Congo, accounting for 70% of the total crop production landscape (Bakelana and Ndungo, 2004). In this region, the crop is predominantly cultivated on smallholdings and in mixtures, with bush beans and taro as the predominant intercrops. To integrate the
Banana plant characteristics at flowering and harvest
Table 1 shows that the reduced model was the best predictor for the banana plant characteristics (i.e. the lowest value for BIC and p < 0.05 for significance of difference with the null model), and was thus used in the subsequent determination of the fixed effects. The fixed effects did not profoundly affect the time to harvest in banana plants (Table 1). Despite this observation, a lower mean time to harvest was observed in banana plants in which four leaves had been retained (Fig. 1a) while
Discussion
Intercropping of bananas in East Africa has increased due to the currently increasing land pressure (Bekunda and Woomer, 1996; Bekunda, 1999; Ntamwira et al., 2013b; Ocimati et al., 2013; Tittonell and Giller, 2013). To intercrop shorter crops such as the legume crops within banana fields, pruning banana leaves is one of the intensification practices applied by smallholder farmers, mainly to meet their household food security and nutritional needs. This practice is aimed at increasing the
Conclusions
Banana leaf pruning despite its current role in the spread of XW disease of banana, is a common practice to allow for banana-legume intercropping and mainly driven by the small land/farm sizes. Leaf pruning improved light penetration to legumes and their yield while it negatively affected the growth and yield of the banana crop. More severe yield reductions occurred when only four leaves were retained, a practice that also resulted in the least land use efficiency compared to when all leaves
Acknowledgement
We are grateful for the financial support from the Belgian Directorate General for Development through the Consortium for Improving Agriculture-based Livelihoods in Central Africa. This research was conducted in the framework of the Roots, Tubers and Banana program of the CGIAR (CRP RTB).
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