Nutrient cycling in an agroforestry system with runoff irrigation in Northern Kenya |
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| Authors: | J Lehmann D Weigl K Droppelmann B Huwe W Zech |
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| Institution: | (1) Institute of Soil Science and Soil Geography, University of Bayreuth, D-95440 Bayreuth, Germany;(2) Blaustein Institute, University of the Negev, Sde Boqer, Israel;(3) Soil Physics Group, University of Bayreuth, D-95440 Bayreuth, Germany |
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| Abstract: | A nutrient balance was determined for sole and alley cropped Sorghum bicolor and Acacia saligna in a runoff irrigation system
in Northern Kenya. Nutrient input including precipitation and runoff, and output through harvest and leaching were measured
for N, P, K, Ca and Mg using adsorption resins, tensiometry and suction cups. Various management scenarios are discussed with
respect to nutrient return. Nutrient input with rainfall was generally low in comparison to nutrient uptake or leaching losses.
The irrigation water, however, constituted an important nutrient input, especially for Ca and Mg. Nutrient export with the
harvest was large for N and K, but can effectively be reduced by a nutrient return with mulch. Nutrient leaching losses from
the topsoil (0–30 cm) were lower in the sorghum monoculture than in the tree-based systems. In the subsoil (120 cm), however,
leaching was effectively reduced by the trees. In the agroforestry system, leaching losses of N under the sorghum were 53%
lower than in the sorghum monoculture. This could be attributed to a higher root abundance and a higher ratio of nutrient
uptake-to-leaching in the agroforestry system than in the monocultures indicating a higher nutrient efficiency. The lower
leaching losses in the agroforestry system compared to the crop monoculture could not compensate for the additional nutrient
export in tree biomass. A nutrient return by mulching crop residues and acacia leaves was essential for a positive nutrient
balance in the agroforestry system. Combining annual and perennial crops provided a higher internal nutrient cycling than
the monocultures.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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| Keywords: | Acacia saligna nutrient balance nutrient leaching resin core soil solution Sorghum bicolor |
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