Rétablissement de la capacité de production de sorgho (Sorghum bicolor [L.] Moench) d'un vertisol dégradé dans la région de l'Extrême Nord du Cameroun

Recovery of sorghum (Sorghum bicolor [L.] Moench) production capacity in degraded vertisols in the Far North Region of Cameroon. In Northern Cameroon, degraded soils represent 10 to 20% of arable land. Recovering the production capacity of these degraded soils is one of the main challenges faced by agriculture in the region. The objective of the present study, conducted from 2007 to 2009, was to examine the possibility of growing sorghum on degraded and bare vertisols. A combination of the following techniques was used in a randomized complete block design: two land preparation techniques (plowing or mounding), two levels of cow dung dust (6 or 12 t·ha-1) and three rates of urea application (0, 50 or 100 kg·ha-1). The soil was sampled at a depth of up to 25 cm and was analyzed for its properties following standard analytical procedures. Critical levels established for tropical soils were used to declare sufficiency or deficiency of soil nutrients within the samples. Sorghum straw and grain yields were obtained and analyzed. Soil characteristics were found to be similar to those of other degraded vertisols found in the Far North Region of Cameroon. The hard top soil layer was found to be unfavorable to the establishment of sorghum. On the other hand, levels of organic carbon (0.85%) and the sum of cations (4.91 meq·100 g-1 of soil) were found to be favorable. The ratio of cations was found to be unfavorable to Ca. Available phosphorus (5.35 mg·kg-1 of soil) and total N (0.04 g·kg-1) were very low. Following the application of treatments, 2.4 to 3.5 t·ha-1 of sorghum straw were produced and 1.3 to 2.8 t·ha-1 of grain were harvested during the experimental period. Soil plowing and mounding successfully disturbed the hard top soil layer. Soil mounding resulted into in a 16% increase in straw production in comparison with soil plowing alone. The application of 12 t·ha-1 of cow dung dust produced an additional grain yield of 17% in 2008 and of 39% in 2009 when compared to plots receiving only 6 t·ha-1. The sorghum yield response to urea was shown to be quadratic. These results suggest that it is possible to rehabilitate the degraded and abandoned vertisols of the Far North Region of Cameroon using appropriate cultural practices, including the application of cow dung dust, soil plowing and mounding, and nitrogen fertilization.