Monitoring Phosphorus Nutrition Of Maize On Four Land Form Technologies In The Vertisols Of The Accra Plains

ABSTRACT A field trial was started in August 1994, during the minor cropping season to investigate the efficiency of four Landforms in the production of maize with special emphasis in phosphorus (P) management in Vertisols at three localities in the Accra Plains of the Coastal Savanna zone of Ghana. The four Landforms were: Flat, Ridged, Ethiopian and Cambered beds. Generally, the soils were low in available P. Raising available P levels in the soil by the addition of fertilizer led to significant increase in dry weight of maize in all the Landforms. On the Cambered bed, however, raising the fertilizer above 50 % of the recommended rate did not cause significant yield increase. The Landforms had significant influence on P uptake and dry matter production. In all instances, the raised beds, i.e. Ridged (R), Ethiopian (EB) and Cambered (CB) significantly outperformed the Flat (F) bed in terms of P uptake and dry matter production. Among the raised beds, the Cambered bed had significantly higher dry matter yield than the Ridged and Ethiopian beds. The relative agronomic efficiency (RAE) of the four landforms were in the order of CB > EB = R > F (P < 0.05). Unlike the Ridged and the Ethiopian beds, the RAE of the Cambered bed at 50 % fertilizer application was higher than the 100 % fertilizer application. Soil organic P formed about 25 % of the total P and this value did not change significantly throughout the growing season. Calcium bound phosphate (Ca-P) was the dominant inorganic P and constituted about 78 % of the active inorganic P in the soils. Iron bound phosphate (Fe-P) was the least and constituted 2 % of the total active inorganic P. The two inorganic P fractions significantly correlated with P uptake and dry matter production. Though both Ca-P and Aluminium bound phosphate (Al-P)_ did not change significantly during the maize growing period, the Fe-P on the other hand reduced to about one-half its initial value. Generally, increase in fertilizer application increased P uptake, with the highest P uptake on the CB and least on the F. A significant Landform x fertilizer interaction was observed for dry matter production when 50 % fertilizer application on the CB out yielded 100 % fertilizer on the F. Generally, there was negative soil available P balance in all the Landforms and at all the rates of fertilizer application at the end of the season.