Fertilization Strategies in Conservation Agriculture Systems With Maize–legume Cover Crop Rotations in Southern Africa

Abstract

Multilocation experiments were established to determine the best strategy for using inorganic fertilizer in conservation agriculture (CA) systems that use green manure cover crops, namely sunhemp, velvet bean and cowpea grown in rotation with maize. The objectives of the study were to determine (i) the effect of half and full rates of basal fertilizer on maize and legume biomass yields, (ii) the residual effects of unfertilized, half and fully fertilized green manure legumes on maize grown after the legumes, and (iii) the residual effect of unfertilized, half and fully fertilized green manure legumes combined with basal and topdressing fertilizer on maize yields. Experimental design was a randomized complete block with basal fertilizer as a treatment in the green manure legumes phase. Previously, in the maize phase, green manure legume species were the main treatment with basal fertilizer as a subtreatment (sunhemp, velvet bean and cowpea: 0, 75, 150 kg ha −1 and 0, 50, 100 kg ha −1 , respectively). Nitrogen was applied in the maize phase at 0, 23, 46, 69 kg N ha −1 as a sub-subtreatment in Malawi. Results showed that inorganic fertilizer is the most effective when applied to the maize, not green manure legumes. Biomass of green manure legumes, sunnhemp 8084 kg ha −1 , velvet bean 7678 kg ha −1 and cowpea 4520 kg ha −1 , was not significantly affected by application of basal fertilizer. Maize production increased after the application of green manure legumes with maize-after-maize, maize-after-velvet bean, maize-after-sunnhemp and maize-after-cowpea, yielding 3804, 5440, 5446 and 5339 kg ha −1 , respectively. Nitrogen increased maize yield regardless of the previously used green manure legumes species. Our results suggest that farmers should apply fertilizer to maize and grow green manure legumes on residual soil in CA systems. Despite growing green manure legumes, smallholders should apply nitrogen topdressing to maize grown using the green manure legumes in some agro-ecologies.

Complementary practices supporting conservation agriculture in southern Africa. A review

“…Smallholders in southern Africa apply residues of different grass species, litter (mixture of leaves and twigs) from the indigenous trees, and litter from fruit trees planted around homesteads (Nyamangara et al 2009;Nyathi and Campbell 1993;Mtambanengwe and Kirchmann 1995;Musvoto et al 2000). Litter derived from Uapaca kirkiana (Benth), Brachystegia spiciformis (Benth), and Julbernardia globiflora (Benth) trees, and thatching grass (Hyparrhenia filipendula (Hochst (Stapf)) are commonly used by smallholders for soil fertility restoration and mulching in southern Africa (Nyathi and Campbell 1993;Mupangwa et al 2016b). Fully mature thatching grass is often not completely grazed by livestock because of its high lignin content, making it available for other purposes, including construction and mulching on the farm.…”

“…Residues can also be availed from leguminous species, such as pigeonpea (Cajanus cajan (L.) Millsp. ), sunnhemp (Crotalaria juncea L.), common rattlepod (Crotalaria grahamiana L.), and fish bean (Tephrosia vogelii L.), whose stover can be slashed and left on the soil surface after they have senesced (Sakala et al 2000;Nyamangara and Nyagumbo 2010;Mupangwa et al 2016b).…”

Bridging the disciplinary gap in conservation agriculture research, in Malawi. A review

“…There is a group of literature, which provides detailed technical prescriptions (n = 20) or information on additional agronomic practices and guidelines (n = 27) that are needed for successful functioning of CA. These practices include fertilizer, herbicide, organic manure (Mupangwa et al 2017b;Fisher et al 2018), agroforestry tree species (Andersson and D'Souza 2014) and seeding patterns including spacing and planting methods (Ngwira et al 2012c(Ngwira et al , 2013Thierfelder et al 2013bThierfelder et al , 2015cThierfelder et al , 2016aBunderson et al 2017;Mupangwa et al 2017b;Mutenje et al 2019), ripping (Thierfelder et al 2015c;Mutenje et al 2019) and basin planting (Thierfelder et al 2015c;Mutenje et al 2019). In the paper by Thierfelder et al (2016a), CA is defined as no-till with residue cover and dibble stick planted maize only in one treatment and maize (Zea mays L.)-cowpea (Vigna unguiculata L.) intercropping in the other-the later following the stringent definition of FAO with all three principles covered while the former being an "incomplete CA-based system".…”

Getting Down to Earth (and Business): Focus on African Smallholders' Incentives for Improved Soil Management

“…Selected evidence for soil-enhancing practices Productivity: Increased production and/or improved quality and value of production Increased yield Legume rotation/forage/cover cropping- (Lal et al, 1978;Sileshi et al, 2008;Franke et al, 2018;Zemek et al, 2018) Perennial intercropping- (Bayala, 2012;Bright et al, 2017) No-till, legume intercropping- (Thierfelder et al, 2016) Organic amendments/biochar addition- (Soma et al, 2018;Kätterer et al, 2019) Planting basins, ridging, weed management- (Dahlin and Rusinamhodzi, 2019) Fertilizer microdosing- (Bielders and, 2015) Precision agriculture, seed treatment- (Aune et al, 2017) Rhizobium inocula and phosphorus fertilization- (Belete et al, 2019) Tied ridging, crop residue incorporation, legume rotation- (Kouyaté et al, 2000) Zaï farming- (Schuler et al, 2016) Reduced costs of production: Decreased input (e.g., fertilizers; crop protection products) and/or labor costs Yield return on labor Planting basins, ridging, weed management- (Dahlin and Rusinamhodzi, 2019) Reduced fertilizer use Perennial intercropping - (Bright et al, 2017) Integrated soil fertility management- (Vanlauwe et al, 2015) Reduced fertilizer in green manure legume rotation- (Mupangwa et al, 2016) Starter nitrogen for cowpea- (Nurudeen et al, 2018) Phosphate rock-legume compost- (Shitindi et al, 2019) Organic amendments- (Soma et al, 2018) Reduced weed/pest pressure Ecological weed management- (Bàrberi, 2019) Legume intercropping/trap crop rotation- (Gbèhounou and Adango, 2003;Khan et al, 2006) Integrated pest management (push-pull)- (Hassanali et al, 2008) Resilience: Decreased variability of production; diversified income sources Increased resilience to drought No-till- (Jemai et al, 2013) Perennial intercropping- (Paterson et al, 1998) Environmental benefits: Accruing both on-and off-farm…”