Efforts have been made in recent years to improve knowledge about soil greenhouse gas (GHG) fluxes from sub-Saharan Africa. However, data on soil GHG emissions from smallholder coffee-dairy systems have not hitherto been measured experimentally. This study aimed to quantify soil GHG emissions at different spatial and temporal scales in smallholder coffee-dairy farms in Murang’a County, Central Kenya. GHG measurements were carried out for one year, comprising two cropping seasons, using vented static chambers and gas chromatography. Sixty rectangular frames were installed on two farms comprising the three main cropping systems found in the area: 1) coffee (Coffea arabica L.); 2) Napier grass (Pennisetum purpureum); and 3) maize intercropped with beans (Zea mays and Phaseolus vulgaris). Within these fields, chambers were allocated on fertilised and unfertilised locations to capture spatial variability. Cumulative annual fluxes in coffee plots ranged from 1 to 1.9 kg N2O-N ha− 1, 6.5 to 7.6 Mg CO2-C ha− 1 and − 3.4 to − 2.2 kg CH4 -C ha− 1, with 66% to 94% of annual GHG fluxes occurring during rainy seasons. Across the farm plots, coffee received most of the N inputs and had 56% to 89% higher emissions of N2O than Napier grass, maize and beans. Within farm plots, two to six times higher emissions were found in fertilised hotspots – around the perimeter of coffee trees or within planted maize rows – than in unfertilised locations between trees, rows and planting holes. Background and induced soil N2O emissions from fertiliser and manure applications in the three cropping systems were lower than hypothesized from previous studies and empirical models. This study supplements methods and underlying data for the quantification of GHG emissions at multiple spatial and temporal scales in tropical, smallholder farming systems. Advances towards overcoming the dearth of data will facilitate the understanding of synergies and tradeoffs of climate-smart approaches for low emissions development.
Tag: pennisetum purpureum
Contour grass strips and tillage affect corn production on Philippine steepland oxisols
Cultivated steeplands in the humid tropics require better soil management systems to meet increasing food demands. The objective of this 4-yr study was to evaluate the following four contour soil management systems for corn (Zea mays L.) production: (i) contour moldboard plowing (CP); (ii) ridge tillage (RT); (iii) natural grass barrier strips plus moldboard plowing (GCP); and (iv) grass strips plus ridge tillage (GRT). Eight successive corn crops were grown in limed and fertilized soil from 1992 through 1995. On a total land area basis (cropped area plus the area occupied by the grass strips), the 1995 mean grain yields for RT (10.8 Mg ha1) and GRT (10.3 Mg ha1) were significantly greater than yields for CP (10.0 Mg ha1) and GCP (9.6 Mg ha1). The corn grain yields for the CP and RT systems before 1995 ranged from 1.3 Mg ha1 in 1992 to 8.4 Mg ha1 in 1993, while comparable GCP and GRT yields ranged from 1.4 to 7.6 Mg ha1 Excluding the area occupied by the grass strips, the GRT system had the highest 4-yr average corn yield (7.3 Mg ha1) followed by the GCP (7.2 Mg ha1), RT (6.9 Mg ha1) and CP (6.7 Mg ha1) systems. Yields improved during the 1994 and 1995 growing seasons when the grass was not permitted to grow as tall. The combination of contour ridge tillage and contour grass strips has potential for sustaining crop productivity on highly erodible steepland soils in the humid tropics.
Leguminous fodder trees: boosting milk production and income for farm families in Kenya
Genetic diversity in Napier grass (Pennisetum purpureum) cultivars: implications for breeding and conservation
Napier grass is an important forage crop for dairy production in the tropics; as such, its existing genetic diversity needs to be assessed for conservation. The current study assessed the genetic variation of Napier grass collections from selected regions in Eastern Africa and the International Livestock Research Institute Forage Germplasm-Ethiopia. The diversity of 281 cultivars was investigated using five selective amplified fragment length polymorphism (AFLP) markers and classical population genetic parameters analysed using various software. The number of bands generated was 216 with fragments per primer set ranging from 50 to 115. Mean percentage polymorphic loci was 63.40. Genetic diversity coefficients based on Nei’s genetic diversity ranged from 0.0783 to 0.2142 and Shannon’s information index ranged from 0.1293 to 0.3445. The Fst value obtained was moderately significant (Fst = 0.1688). Neighbour-joining analysis gave two distinct clusters which did not reflect geographical locations. Analysis of molecular variance showed all variance components to be highly significant (P < 0.001), indicating more variation within (91 %) than between populations (9 %). Results suggested moderate genetic differentiation among Napier grass populations sampled, which could imply a high germplasm exchange within the region. The AFLP markers used in this study efficiently discriminate among cultivars and could be useful in identification and germplasm conservation.
Availability and use of dry season feed resources on smallholder dairy farms in central Kenya
A cross-sectional survey on 41 farms followed by six weeks monitoring of dairy cattle feeding on ten smallholder dairy farms in central Kenya was conducted to investigate the use, availability and quality of dry season feed resources. Fodder production was largely from Napier grass (Pennisetum purpureum) grown on small plots and contour strips where it acts both as a fodder source as well as a biological barrier to soil erosion. There is a need to broaden the choice of fodder crops on such farms to provide a wide range of harvesting management options and to avoid total loss in case of pest or disease outbreaks. Intercropping of Napier grass with leguminous fodder trees could boost the quantity and quality of herbage production especially during the dry season. Roughage from a variety of sources was utilised during the dry season in addition to Napier grass. Among the herbages, leguminous feeds had the lowest potential dry matter degradability while weeds harvested from cropland and roadsides had the highest. Energy and protein intake from the roughage fed to grade dairy cattle during the dry season may be insufficient to meet the requirements of these animals due to the high levels of fibre concentration (acid detergent fibre and neutral detergent fibre (ADF and NDF)) in them. It is recommended that the scope for alternative sources of improved roughage such as Napier/calliandra mixtures, to boost the energy, protein and overall dry matter provision on the farms should be investigated further.
Combining napier grass with leguminous shrubs in contour hedgerows controls soil erosion without competing with crops
We established hedges/barriers of calliandra (Calliandra calothyrsus Meissner), leucaena (Leucaena trichandra (Zucc.) Urban)) and napier grass (Pennisetum purpureum Schumach) and combination hedges of either calliandra or leucaena with napier grass on slopes exceeding 5% to study the effect of vegetative barriers on productivity of arable steeplands in central Kenya. Hedges/barriers were pruned regularly and biomass incorporated into the plots.Hedge plots were monitored for soil fertility, soil losses and maize crop yield changes. Inorganic-N concentration in the tree hedge plots was higher than in the control and napier barrier plots after 20 months. Napier grass barriers were the most effective in reducing erosion losses across the two seasons. The effectiveness of napier grass to significantly reduce soil erosion was detectable in one year old napier barriers. Soil loss from all the other one year old vegetative treatments was similar to soil loss from the control. Seventeen month old combination hedge plots recorded lower soil losses than tree hedges of the same age (P = 0.012). Maize crop yields throughout the trial period were high and similar for leguminous and combination hedge plots, but lower in the napier grass and control plots.Overall, we observed that the combination hedges seemed to provide a win-win scenario of reduction in soil erosion combined with improvement of maize crop yields and soil fertility enhancement.We conclude that vegetative hedges have a potential for improving soil productivity in arable steep-lands of the central highlands of Kenya, and that in adoption of vegetative hedges for this purpose there are trade-offs between soil conservation, soil fertility and maize crop yields to be considered.