Plant Residue-Derived Organic Carbon Input into Soil in African Indigenous Vegetable Production Systems
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Date
2016
Authors
Onyuka, Enos
Nambafu, Godfrey
Bessler, Holger
Adam, Anna
Andika, Darius O.
Gweyi-Onyango, Joseph P.
Mwonga, Samuel
Engels, Christof
Journal Title
Journal ISSN
Volume Title
Publisher
Tropentag
Abstract
Food production in sub Saharan Africa is constrained by low soil fertility, whereby soil organic
matter (SOM) is key factor regulating many soil functions that determine the yielding ability
of soils. SOM content is influenced by the mass and quality of organic carbon input into soil. In
smallholder farming systems manure and composts are scarce, and only small fractions are allocated
to soil amendment due to alternative use as feed and fuel. Therefore, organic matter input into soil
is often restricted to plant residues remaining in the field. In this study, we quantified the effects of
species and harvesting method on the mass and quality of plant-derived carbon input into soil with
the aim to improve soil fertility management in African indigenous vegetable (AIV) production
systems.
Five AIV species (amaranthus - Amaranthus cruentus, cowpea - Vigna unguiculata, African kale
- Brassica carinata, African nightshade - Solanum scabrum, spider plant - Cleome gynandra) and
common kale (Brassica oleracea acephala) were grown in a field experiment. Plants were harvested
by two different methods, which are both commonly used in Kenya: Plants were either pulled out
with some coarse roots adhering to the stems or cut about 5 cm above the soil surface. Leaf litter,
above-ground plant residues and below-ground residues (coarse root, fine roots in 0–0.3m and 0.3–
0.6m soil depth) were quantified and analysed for C content. The humification efficiency of plant
residues was determined in incubation studies under controlled conditions.
Input of plant residue-derived organic carbon into the soil significantly differed among species
with minimum of 0.3 kg C m−2 for cowpea and maximum of 0.8 kg C m−2 for amaranthus. In all
species, input with leaf litter was negligible, while the contribution of fine roots to C input varied
between about 40% in spider plant and 80% in cowpea. Pulling out instead of cutting plants
reduced carbon input by 14% in cowpea and nearly 60% in African kale and spider plant.
It is concluded that in AIV production systems with low availability of organic fertilisers species
selection and harvesting method are important determinants for soil C dynamics and fertility.
Description
Research Article
Keywords
Coarse roots, Fine roots, Harvest method, Humification, Leaf litter, Stubble
Citation
Tropentag, September 18-21, 2016, Vienna, Austria