The contribution of Stylosanthes guianensis to the nitrogen cycle in a low input legume-rice rotation under conservation agriculture

Abstract

Background and aims Legumes integrated in crop rotations are intended to improve crop nitrogen (N) supply and yield. In conservation agriculture (CA) systems under low input conditions on highly weathered tropical soils, experimental evidence for these benefits is lacking. To understand the mechanisms and evaluate the impact of the legume N on the subsequent crop, an in-depth study on N dynamics in the soil-plant system was conducted. Methods In Madagascar, a CA based crop rotation with the perennial forage legume Stylosanthes guianensis (stylo) and upland rice (rice/stylostylo -rice/stylo) was established under three fertilization regimes. In addition, rice was grown in a non-CA bare fallow rotation without fertilizer. Over the three years N 2 fixed in stylo shoots, the incorporation of stylo shoot (mulch) N into soil N pools and mulch N uptake by rice was quantified using 15 N techniques and mulch and stylo root residue decomposition was investigated in a litterbag study.Results N 2 fixed in stylo shoots ranged from 96 to 122 kg N ha −1 . Between 50 to 70% of stylo mulch and root residues decomposed during the third cropping season. Without fertilizer, grain yield of rice after the fallow with stylo was about 70% greater than after bare fallow, corresponding to 11 kg N ha −1 greater N uptake. Recoveries of stylo mulch N after rice harvest were on average 64% in soil, with about 3% in each of the microbial and mineral N pools, with 39% on the soil surface, and 6% in the rice crop. The N input via stylo seed, leaf litter and belowground N totalled about three times the amount of N contained in stylo mulch, which usually is considered as major rice N source. Conclusions Legumes, like stylo, can improve crop N supply and yield in low input CA cropping systems on highly weathered tropical soils. To explain the impact and mechanisms involved requires a consideration of all legume-N components beyond the mulch N present at the onset of the rice-cropping season. Keywords 15 N . Mulch . Symbiotic N 2 fixation . Madagascar . Litterbag study . Ferralsol . N recovery Abbreviations CA Conservation agriculture CA-NON CA based upland rice -stylo fallow rotation were rice received no fertilizer CA-FYM CA based upland rice -stylo fallow rotation were rice received farmyard manure CA-MIN CA based upland rice -stylo fallow rotation were rice received mineral fertilizer

Mixed outcomes from conservation practices on soils and Striga-affected yields of a low-input, rice–maize system in Madagascar

“…Compared to the conventional rice-maize rotation (CONV), the combination of no till, stylosanthes intercropping and crop residue mulching (CAST) led to a significantly higher total soil-N concentration over time, probably because of the species capacity of biological nitrogen fixation combined with the high biomass production. This confirms a previous study conducted in the same area, showing that intercropping with S. guianensis improved nitrogen supply to rice (Zemek et al 2018 prevailing soil P deficiencies. Indeed, soil nitrogen concentration can be significantly improved when residues from legumes are not removed from the field (Vanlauwe and Giller 2006).…”

Nitrogen and phosphorus uptake from isotope‐labeled fertilizers by sorghum and soil microorganisms

“…The 15 N atom excess in the extracts of fumigated and non-fumigated samples was determined using the oxidation-diffusion method as described in Zemek, Frossard, Scopel, and Oberson (2018). The 15 N atom excess in the SMB (% excess 15 N mic ) was then calculated using the 15 N mass balance as described in Douxchamps et al (2011).…”

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…”