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African Crop Science Journal
African Crop Science Society
ISSN: 1021-9730
EISSN: 1021-9730
Vol. 6, No. 1, 1998, pp. 19-28
Bioline Code: cs98003
Full paper language: English
Document type: Research Article
Document available free of charge

African Crop Science Journal, Vol. 6, No. 1, 1998, pp. 19-28

 en Soil organic carbon fractions in a long-term experiment and the potential for their use as a diagnostic assay in highland farming systems of Central Kenya
Kapkiyai, J.J.; Karanja, N.K.; Woomer, P. & Qureshi, J.N.

Abstract

Soil organic matter fractions provide insight into soil quality and the maintenance of crop productivity in smallhold cropping systems. Soil organic carbon (SOC) pools were measured and compared to crop performance during the eighteenth year of a long-term field experiment established on a Humic Nitisol at the Kenya Agricultural Research Institute. Maize stover retention (+S), cattle manure (+M, 10 t ha-1 yr-1) and fertilizer inputs (+F, 120 kg N and 23 kg P ha-1 yr-1) were compared in a 2 x 3 factorial arrangement in a manner that is broadly reflective of farmer resource management options. Maize (Zea mays) and beans (Phaseolus vulgaris) were cultivated in rotation during the long (March-June) and short (October-December) rains of each year, respectively. Maize yields ranged between 1.21 (+S) and 5.21 t ha-1(+SMF). Beans produced between 0.14 (-S) and 0.77 t ha-1(+SMF). Total crop yields were significantly affected by manure and fertilizer addition (P<0.001) but not stover retention (P = 0.13). Soil microbial biomass carbon (MBC, r = 0.63), particulate organic carbon (POC, r = 0.82) and its density fractions varied significantly with combined maize and bean yields in plots not receiving fertilizers. Only MBC was significantly correlated with crop yields in the inorganically fertilised treatments (r = 0.50). Livestock manure contributed to POC to a greater extent than did retention of maize stover or the addition of fertilizers. Of the different Ludox density fractions of POC, the lightest (<1.13 g cm-3) was best correlated with crop yields (r = 0.73) and the heaviest fraction (>1.37 g cm-3) least correlated with yield (r = 0.37). When 190 Central Kenyan smallhold 'households' were surveyed, 79% were classified as maize-bean farmers and 79% of these relied on combinations of stover, manure and fertilizers to maintain soil fertility. Thus, the long-term experiment at Kabete is broadly applicable to the surrounding farming community. Soil organic matter fractions were more favourably influenced by addition of livestock manure than the retention of maize stover, suggesting that the widespread farmer practice of harvesting maize stover as animal feed and returning animal wastes may effectively contribute to soil fertility management.

Keywords
Particulate organic carbon, Ludox fractions, soil microbial biomass, East African Highlands, Kenya, long-term experiment

 
 fr
Kapkiyai, J.J.; Karanja, N.K.; Woomer, P. & Qureshi, J.N.

Résumé

Les fractions de la matiere organique du sol constituent un element important pour la qualite des sols et pour le maintien de la productivite des cultures dans les sysemes de production de petits fermiers. Les poold de carbone organique du sol etaient determines et correle avec la performance des cultures a la huiteme annee d'un essai de longue duree installee sur un Nitosol restitution des chaumes de mais (+S), l'apport du fumier de fer,e (+M), 10t ha-1 an-1)etaient testes dans un essai factoriel 2 x 3 conccu de maniere a ressembler le plus aux options d'amenagement de ressource par l'agriculteur. Le mais (Zea mays) et la haricot (Phaseolus vulgaris) etaient cultives en rotation chaque anne, respectivement pendant la longue (mars-juin) et la petite (octobre-decembre) saisons de pluie. Les rendements de mais ont varie de 1.21 (+S) et 5.21t ha-1(+SMF). Le haricot a produit entre 0.14 (+S) et 5.21 t ha-1(+SMF). Les rendements totaux des cultures etaient tres significativement affectes par l'application du fumier et des engrais mineraux (P<0.001); les chaumes de maiz pa contre n'avait pas d'effeet significatif. Le carbone dans la biomasse microbienne du sol (MBC, r = 0.63), le carbone organique dans les particules de sol (MBC, r = 0.82) et ses fractions a base de densite variaient significativement avec le rendement du mais et du haricot dans les parcelles n'ayant pas recu d'engrais mineraux. Seul, le MBC etaint significativement correle avec le rendement des cultures dans les parcelles fertilisees aux ebgrais mineraux (r = 0.50). Le fumier de ferme a miux contibue au POC que les chaumes de mais ou les engrais mineraux. Parmi les differentes fractions Ludox du POC, la fraction la plis legere (<1.13g cm-3) etait la mieux correlee avec le rendement des cultures (r = 0.73) tandis que la plus lourde (>1.37 g cm-3) montraint la plus faible correlation avec le rendement (r -0.37). Lors de l'enquete de 190 petits exploitants du Kenya Centre, 79% de fermiers ont ete identifie comme planteur de Mais-haricot, 79% de ces fermiers utilisaient a la fois les chaumes de mais, le fumier et l'emgrais, mineral pour ,aintenir la fertilite des terres. Ainsi, l'essai de longue duree de Kabete est largement applicable au systeme de production des agriculteurs d'aux environs. Les fractions de la matiere organique du sol etaient plus favorablement influencees par l'application du fumier que la restitution des chaumes de mais. Ceci monte que la pratique repandue des agriculteurs de recolter les chaumes de mais pour les utiliser comme fourrage et de collecter ensuite le fumier pour fertiliser les champs peut effectivement contribuer a la gestion de la fertilite des sols.

Mots Clés
Carbone organique en particules de sol, fractions Ludox, biomasse microbienne du sol, hautes terres d'Afrique de l'Est, Kenya, essai de longue duree.

 
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