On-farm evaluation of yield and economic benefit of short term maize legume intercropping systems under conservation agriculture in Malawi
Highlights
► Principles of conservation agriculture had an overriding effect on maize yield due to better soil water balance. ► Maize legume intercropping increased the quantity of residues produced and retained as surface mulch. ► Maize legume intercropping under CA resulted in more than double gross margin compared to conventional tillage. ► For extensive adoption, considerations on residues management; and markets for legume seed and produce are required.
Introduction
Agriculture in the next decade will have to produce more food from less area of land through more efficient use of natural resources with minimal impact on the environment in order to meet the growing population demands (Hobbs et al., 2008). This study was conducted in southern Africa, a region barely self-sufficient in food grains, with a net import of 10% if South Africa is excluded (FAOSTAT, 2010). Agriculture is the mainstay of Malawi's economy contributing 35% of the gross domestic product (GDP). Maize is the major staple crop occupying about 80% of the land area under cultivation (Ito et al., 2007) and accounting for more than 80% of the population's caloric intake (MoAFS, 2011). Currently farmers face four major constraints. First, over the past 25 years, average maize yields in Malawi have fluctuated around an average of about 1.1 t ha−1 until 2005 when there has been an increase in maize yields due to the launch of an ambitious smallholder Farm Input Support Programme (FISP) (Fig. 1). Degraded and infertile soils as a result of continuous monocropping and insufficient organic matter recycling coupled with occurrence of rainfall variability marked by frequent dry spells account for low crop yields (Kumwenda et al., 1997, Wall, 2007, Rockström et al., 2009). It is reported that the recent fertilizer and seed subsidy programs have had impressive effects on national yields. In the 2005/06 season, the national average maize yield jumped from 1.1 to 1.6 t ha−1. In the subsequent 2006/07, 2007/08, 2008/09, 2009/10 and 2010/11 seasons estimated average maize yields were 2.6 t ha−1, 1.6 t ha−1, 1.7 t ha−1, 1.8 t ha−1 and 2.1 t ha−1 respectively (Denning et al., 2009, MoAFS, 2011). However, even with subsidized inputs; the gap between actual and potential yield is still very wide. Second, smallholder farmers have limited access to adequate amounts of farm inputs such as fertilizer and improved seed due to low purchasing power and weak value chains (Chilowa, 1998). The price offered for maize grain is low compared to cost of production – providing little incentive to farmers to produce above subsistence. Third, the land area available for cropping is declining due to increase in population. Typical cultivated land holding sizes range between 0.2 and 3 ha (Ellis et al., 2003, World Bank, 2007). This implies that increasing agricultural production through area expansion is no longer feasible and therefore increasing efficiency of agricultural growth and crop productivity forms an essential component of improving food security. Fourth, labour availability for farming operations in the predominantly maize-based farming systems has become a critical issue due to combined effects of the HIV/AIDS pandemic and constant migration of rural labour to urban centres. Smallholder farmers spent a lot of energy in moving the soil during ridging (Materechera and Mloza-Banda, 1997).
The current cropping systems characterized largely by continuous monocropped maize are not sustainable – they degrade the natural base and are labour intensive (Mloza-Banda, 2005, Ito et al., 2007). There has been increasing realization that the solution to maintenance and improvement of soil fertility cannot be solely through use of inorganic fertilizers. This has led to the expansion of the FISP from 2008 to include legume seeds such as pigeonpea that can fix nitrogen biologically from the atmosphere. However, reducing soil degradation only through application of nutrients is not adequate (Wall, 2007). A shift towards more sustainable cropping systems such as conservation agriculture (CA) may help in reversing soil degradation; reducing labour time and improve production. CA is characterized by three principles which are linked to each other in a mutually reinforcing manner. CA is based on (a) minimum soil disturbance (b) permanent soil cover with living or dead plant material and (c) diversified crop rotations and associations with leguminous crops (FAO, 2009). CA systems have been adopted by farmers in the United States of America, Latin America, and Australia mainly on large scale commercial farms. For sub-Saharan Africa smallholder farmers this cropping system is still new and areas under CA are small (Derpsch et al., 2010). Important benefits of CA among others include greater rainfall infiltration resulting in increased rainfall use efficiency (Rockström et al., 2009, Thierfelder and Wall, 2010), early planting (Haggblade and Tembo, 2003), reduction in soil erosion (Chuma and Hagmann, 1995), enhanced soil biological activity (Nhamo, 2007, Thierfelder and Wall, 2010) and reduction in amount of labour hours (Ito et al., 2007). Yet most of the benefits have not considered economic analyses of CA and non-CA technologies. Recent studies in sub-Saharan Africa showed better economic returns in CA compared to traditional practices (Guto et al., 2011, Mazvimavi and Twomlow, 2009). Limited research has been conducted on CA systems in Malawi. One study (Chigowo and Saka, 2011) showed that reduced tillage plots had more nitrogen available to crops and higher soil organic matter. Short term research (studies of about two years each) has shown that reduced tillage on soil ridges, involving zone/spot tillage on existing ridges, or mini-mounds between ridges, has produced maize yields similar to those obtained on freshly remade ridges (Materechera and Mloza-Banda, 1997). Even though similar yields were obtained by Sasakawa Global 2000, conservation tillage practices resulted in savings in terms of labour and time (Ito et al., 2007). These past efforts concentrated on zero tillage and residue retention without any consideration of crop rotation or association. As stated earlier smallholder farmers in Malawi are constrained by small landholdings and are thus hesitant to dedicate part of their fields to other crops other than maize, their staple crop. Intercropping maize with leguminous crops may play an important role in enhancing productivity, increasing farmers’ incomes, sustaining and improving soil fertility; and reducing labour shortages. The objective of this study was to investigate the short term effects of different conservation agriculture cropping systems both monocropped and intercropped maize on soil quality, crop productivity and profitability.
Section snippets
Description of experimental sites
This study was conducted over three years (2008–2011) in two communities, i.e. Balaka market and Ntonda sections in Manjawira Extension Planning Area (EPA), Ntcheu district, Lilongwe Agricultural Development Division (ADD). Balaka market section is located between latitudes and longitudes of 14°56′S, 34°53′E and Ntonda section is located between latitudes and longitudes of 14°58′S, 34°44′E on altitudes of 744 and 908 m above sea level respectively. Both sections are characterized by unimodal
Total vegetative biomass production by maize and legumes
Total above ground biomass minus grain including maize and legume biomass for each cropping system over the study period are presented (Table 2). Average total biomass production over the study were 2414, 3360, 4896, 4501, 4368 kg ha−1 for CP, CAM, CAML, CAMM, CAMP respectively in Balaka market section. In Ntonda section, average total biomass production over the study were 2522, 4057, 4488, 3850, 4541 kg ha−1 for CP, CAM, CAML, CAMM, CAMP respectively. In Balaka market, in the first season only
Biomass production and retention
The total amount of vegetative biomass produced in farmers’ fields was highest when legume crops were intercropped with maize (4440 kg ha−1) followed by CA sole maize (3709 kg ha−1) and lowest in CP (2468 kg ha−1). Highest total biomass was obtained in CA maize–legume intercrops due to a larger or equivalent biomass production by maize and to the additional grain legume crop biomass. Crop residues were incorporated into the soil during ridging in CP plots and were retained as surface mulch in all CA
Conclusion
CA practices tested in farmers’ fields gave improved yield of maize with no tillage, residues retention and intercropping with legumes. It was possible to increase total biomass in farmers’ fields using intercropping systems with legumes without a reduction in yield of the main maize crop. Long term solutions involving communities on the role of crop residues in reversing soil degradation becomes an important aspect if crop residues are to be retained amidst fears of termites, rodent hunting,
Acknowledgements
We wish to thank the farmers and Government of Malawi Manjawira EPA Agricultural Extension Development Officers (AEDO) for their enthusiasm, collaboration and support during project implementation phase. We also wish to thank the Royal Norwegian Embassy through Agricultural Research and Development Programme (ARDEP) for funding the project. The opinions expressed in this paper are those of the authors.
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