Growth and yield of eight agroforestry tree species in line plantings in Western Kenya and their effect on maize yields and soil properties.

Abstract

Between October 1988 andAugust J992,field experiments were carried out in West Kenya to evaluate the suitability of Leucaena leucocephala, L. collinsii, Gliricidia sepium, Calliafuira calothyrsus, Sesbania. sesban, S.· giandiflora, Senna siamea and S. spectabilis to provide a range' of agroforestry products and services. The initial objective was to establish the growth rates ,md wood 'analeaf yields of these tree species, when planted in single rows. After the initial evaluation, it was evident that valuable additional information could be' collected if the trees were converted to hedges and their effe<:t.on intercroppedmaize and soils was studied. At 21 months after planting, different species and provenances ranged in height between 3.5 and 6 m and varied considerably in phenotypic; appearance. Wood production (I988-1990)variedfrom3to 3~.8t ha -I imdJeaf production.varied from 0.62 to. iO.I·.t ha-l. During intercropping (1990~ 1992), leaf prOductionvaried from 0 to '10.9t ha -1. Maize yields were higher in .association with Leucaena and Gliricidia than with. (:alliandra. Sesbania and Senna.Cumulatiyemaize grain and stover yields over four seasons were positively correlated with the total amouritof tree leaves applied (r2 range; 0.70-0.';15). The effect oftreeJeaf mulch on crop yields decreased over time for:all species. Leaves with high nutrient contents, which decompose fast (Leucaena. Gliricidia; Sesbania)are likely to helVebeen more effectivejnsustaining' c;ropyields •. thiln leayes with lower I)utrient contents (Senna) or more .cOmplex.decol11Positionpattellls ..• (Calliandra). iSimple ..~..'leaf il)put'"'-cfoP.output' ,.·budgets •t.o• ·caIcU~lltethe·.reserves for· N;.··P.·•.<lmt .Kin •d•ifferent·..sys~ms ••• explained crop yield differences in some' cases. Compated to the fertility status of "zero-mulch" control plots, the.status of .soil C,N,P, K, Ca, Mgarid S wilsto varying degrees improved under Leucaena. Gliricidiaand Sesbanici; much less under Calliandra but not under Senna. Firstseason grain yields were related to the soil fertility status at the end of the tree fallow. The results of these experiments suggest that under subhumidtropical conditions with soils of relatively poor nutrient statu:;, where light and water are not likely to be the major limiting factors to crop production,the application of sufficient quantities of high quality. tree mulch may positively influence maize yields. When agroforestry tree species with contrasting decomposition and nutrient release patterns are evaluated jointly, it is more difficult to demonstrate a general relationship between quantities of mulch applied and improvements in crop yields and soil fertility levels..Therefore, further chemical, physiological and phenotypic characterization of tree species with potential for fallow and intercropping systems is required.