Reduced tillage, mulching and rotational effects on maize (Zea mays L.), cowpea (Vigna unguiculata (Walp) L.) and sorghum (Sorghum bicolor L. (Moench)) yields under semi-arid conditions

Abstract

Proponents of conservation agriculture (CA) argue that the CA approach offers the greatest opportunity to increase the productivity in smallholder agro-ecosystems. This study was designed to assess (1) first year maize, cowpea and sorghum yield responses to a combination of reduced tillage and mulching and (2) maize yield responses to rotation with cowpea and sorghum in reduced tillage systems. Two conservation tillage methods (ripping and planting basins) combined factorially with seven mulch levels (0, 0.5, 1, 2, 4, 8 and 10 t ha −1) were compared with conventional mouldboard ploughing. The experiment was run for four consecutive growing seasons allowing for a rotation of maize, cowpea, sorghum and maize in some fields used in the study. Crop yields were determined across all tillage and mulch combinations in each year. Tillage system had no significant effect on maize yield while maize grain yield increased with increase in mulch cover in seasons that had below average rainfall. Mulching at 2-4 t ha −1 gave optimum yields in seasons with below average rainfall. Tillage system and mulching had no significant effect on cowpea yield when soil moisture was not limiting. However, the ripper and basin systems had 142 and 102% more cowpea grain than the conventional system in 2006/2007 because of differences in planting dates used in three systems and poor rainfall distribution. The conventional and ripper systems gave 26 and 38% more sorghum grain than the basin system. Rotating maize with cowpea and sorghum resulted in 114, 123 and 9% more grain than first year maize, maize-maize monocrop and maize-cowpea-maize in the conventional system. In the ripper system, maize-cowpea-sorghum-maize rotation gave 98, 153 and 39% more grain than first year maize, maize-maize monocrop and maize-cowpea-maize rotation. In the basin system, maize-cowpea-sorghum-maize rotation gave 274, 240 and 43% more grain than first year maize, maize-maize monocrop and maize-cowpea-maize rotation. However, long term studies under different soil, climatic and socioeconomic conditions still need to be conducted to substantiate the observations made in the reported study.

Conservation agriculture in Southern Africa: Advances in knowledge

“…In Zimbabwe, the positive impact of CA on soil aggregate stability was observed on both light and heavy textured soils under semi-arid and sub-humid conditions 30 . In the semi-arid southern regions of Zimbabwe, bulk density of a clay loam soil decreased over time in CA systems (rip-line seeding systems and planting basins) compared with the conventional practice 68 . Soil bulk density is a function of soil texture, SOC content and aggregate stability 69 .…”

“…Under semi-arid conditions of southern Zimbabwe, CA (planting basin and rip-line seeding systems) produced 102-142% more cowpea grain compared to conventional practice in a drought year 68 .…”

“…However, these past researches were largely conducted within experimental stations and did not take into account socio-economic constraints in real farm situations that could hinder the widespread adoption of CA. Recently, more studies reporting results from onfarm and on-station trials have been published concentrating on some of the above-mentioned challenges and constraints 28,37,68,73,86,94,96,97,99,101,102,104,[113][114][115][116] .…”

Fodder production, yield and nodulation of some elite cowpea (Vigna unguiculata [L.] Walp.) lines in central Malawi

“…The crop forms an excellent crop cover for suppressing weeds while at the same time providing soil erosion control (Valenzuela and Smith, 2002). Cowpeas are also considered suitable as cover crops in conservation agriculture systems (Mupangwa et al, 2012). Like many legumes, cowpeas are also important in the rotation or intercropping cereal crops where cowpea serves as a trap crop by helping to reduce the seed bank of striga spp, parasitic weed of cereals (Berner et al, 1996;Kabambe et al, 2005;Carsky et al, 1994).…”

Evidence and Lessons Learned from Long-Term On-Farm Research on Conservation Agriculture Systems in Communities in Malawi and Zimbabwe

“…These constraints for example lack of access to critical inputs (improved seed, fertilizers, herbicides and specialized tools or machinery) and dysfunctional markets [18,19] which are general limitations to all farming enterprises in the area. More specifically to CA, these constraints are competition for crop residues in mixed crop-livestock systems [20][21][22], weed control in the absence of effective herbicides [23][24][25][26][27] and also the mindset of farmers that agriculture is only possible and adequate if the soil is tilled [1,28].…”