Soil Fertility Studies with Compost and Igneous Phosphate Rock Amendments in Malawi

Oxide mineralogy of acid tropical soils contributes to the problem of phosphorus (P) deficiency due to P sorption. The objectives of this research were to evaluate composting methods for improving the availability of phosphorus in igneous low grade (low reactivity) Tundulu phosphate rock and to test their effect on maize (Zea mays L.) yield. The treatments included two composting materials (cattle manure and maize stover) which were applied at 3 t ha-1. Phosphate rock, was composted at three levels: 50, 75 and 100 kg P2O5 ha-1. Epigeic earthworms were introduced into phospho-composts of manure. Sole manure and crop residue composts were also prepared. Three levels of phosphorus were also applied as direct application of phosphate rock. Single super phosphate (SSP) was used as a standard treatment at the rate of 20 kg P2O5 ha-1. There were 16 treatments in total. The experiment was arranged as a Randomised Complete Block with 3 replications. Soil analysis for P has shown no significant differences among treatments in improving the status of P in the soil at both Lunyangwa and Bembeke experimental sites both at seedling and harvest stages of maize, and among sampling times during the first season (1997/98). All P values were below the critical value for P in the soil and therefore maize yield realised was far below the potential for all the treatments.La mineralogie des oxides de sols tropicaux contribue au probl\ue8me de d\ue9ficience du P due \ue0 sa fixation. Les objectives de cette recherche \ue9taient d\u2019\ue9valuer les m\ue9thodes de compostage pour am\ue9liorer la disponibilit\ue9 du phosphore dans l\u2019indig\ue8ne roche phosphat\ue9e de Tundulu \ue0 faible r\ue9activit\ue9 et de tester son effect sur le rendement du ma\uefs (Zea mays L.). Les traitements comprenaient deux materiels de compostage (fumure de vache et les r\ue9sidus du ma\uefs) \ue9taient appl\ueequ\ue9s \ue0 un taux de 3 tones ha-1. La roche phosphat\ue9e, qui \ue9tait compost\ue9e \ue9tait \ue0 trois niveaux: 50, 75 et 100 kg P2O5 ha-1. Les verres de terre \ue9taient incorpor\ue9es dans 3 additionnelles fumures de composte de phosphore. Seule la fumure et les compostes de r\ue9sidus de culture ont \ue9t\ue9 pr\ue9par\ue9s. Trois niveaus de phosphore ont \ue9t\ue9 aussi appliqu\ue9s comme une application directe de la roche phosphat\ue9e. Le superphosphate simple (SSP) a \ue9t\ue9 utilis\ue9e comme un traitement standard \ue0 un taux de 20 kg P2O5 ha-1. Les traitements \ue9taient 16 au total. L\u2019essai \ue9tait conduit dans un bloc compl\ue8tement randomis\ue9. L\u2019analysis du sol pour le P a montr\ue9 qu\u2019il n\u2019y avait pas de difference significative entre traitements dans l\u2019am\ue9lioration de la situation du P dans le sol des sites experimentaux de Lunyangwa et Bembeke \ue0 la germination et au stade de recolte du ma\uefs, et entre les p\ue9riodes d\u2019echantillonnage pendant la premi\ue8re saison (1997/98). Toutes les valeurs du P \ue9taient en dessous de la valeur critique du P dans le sol et ainsi le rendement du ma\uefs obtenu \ue9tait beaucoup inf\ue9rieur au rendement potentiel pour tous les traitements