Case Study 2 Kenya

Arid and semi-arid lands occupy two-thirds of Kenya (Nandwa et al., 1999). Erratic rainfall and poor fertility as a result of intensive cultivation are the main limiting factors of plant productivity. Droughts have also affected farming livelihoods.

Futchimiram

Kaska

KSS3 2+ NG, harvest only grain irmn IF(100 kg ha-1 urea), NG IT^l PR (0.5 t ha-1 y-1), NG

5y F, 5 y C, 2 applications FYM 3 t ha-1, GR IT~n CC, FYM 1.5 t ha-1 y-1, GR

WW CC: millet-cowpea ^^ C-F, FYM 3 t ha-1, to millet rmm CC, FYM 3 t ha-1, to millet

BSSSi NG, harvest aboveground

UTim CC, millet-cowpea rx^l FYM 1.29 t ha-1 y-1,F, GR, harvest only grain NGRs, harvest only grain

Tumbau m

TTTTK IF (110 kg ha-1 urea) 688888 FYM 3.75 t ha-1 y-' irmn FYM 6.75 t ha-1 y rx^l FYM 3.75 t ha-1 y P^l FYM 6.75 t ha-1 y ir~n FYM 6.75 t ha-1 y add nitrogen-fixing trees plant residues 2 t ha-1 harvest only grain

CP:

Current practice

PR:

Plant residues

CC:

Continuous cultivation

F:

Fallow

NG:

No grazing residues

C:

Cultivation

IF:

Inorganic fertilizer

FYM:

Farmyard manure

GR:

Grazing residues

Figure 21.1 Average annual change in soil carbon stock under various practice scenarios (CENTURY) for the case study 1: Nigeria.

Annual or multiple cropping is practiced with occasional fallow periods. CENTURY was run to equilibrium using a grassland tree scenario with grass fires every 10 years and major fires every 30 years at four farmland sites: Darjani, Kaiani, Kymausoi, and Athi Kamunyuni. CPs were compared with CC, burn residues (BR), inorganic fertilizers (IF), and FYM applications (Figure 21.2).

The practices that led to increased CS were the addition of organic material in the form of farmyard manure and plant residues, particularly when systems are at steady state or near. Removal of fallows resulted in losses of 0.1 metric tons C ha-1y-1. In this case, the use of inorganic fertilizers was also inadequate as a sole source of plant nutrients. The combination of legumes in rotations, 2 to 4 metric tons ha-1 year-1 of farmyard manure in addition to 0.6 metric tons ha-1 year-1 of plant residues results in the highest rate of CS in all dryland cases: 0.7 metric tons C ha-1 year-1.

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