Legume rotation effects on early growth and rhizosphere microbiology of sorghum in West African soils

Abstract

Cereal yield increases in legume rotations on west African soils were the subject of much recent research aiming at the development of more productive cropping systems for the mainly subsistence-oriented agriculture in this region. However, little has been done to elucidate the possible contribution of soil microbiological factors to these rotation effects. Therefore a pot trial was conducted using legume rotation and continuous cereal soils each from one site in Burkina Faso and two sites in Togo where cropping system experiments had been conducted over 4 yrs. All soils were planted with seedlings of sorghum (Sorghum bicolor L. Moench). From 21 days after sowing onwards relative growth rates in rotation soils were higher than in the continuous cereal soils, resulting in between 69 and 500% higher shoot dry matter of rotation sorghum compared to sorghum growing in continuous cereal soils. Across sites rotation soils were characterized by higher pH, higher microbial N and a lower microbial biomass C/N ratio and, with the exception of one site, a higher fungal biomass in the rhizosphere. The bacterial and eukaryal community structure in the soil, assessed by denaturing gradient gel electrophoresis (DGGE), differed between sites. However, only at one site differed the bacterial and the eukaryal community structure in the rotation soil significantly from that in the continuous cereal soil. Although the results of this study confirmed the marked plantgrowth differences between sub-Saharan legume-rotation soils and their continuous cereal counterparts they also showed the difficulties to differentiate possible microbiological causes from their effects.

Nematode infestation and N-effect of legumes on soil and crop yelds in legume-sorghum rotations

“…As observed by other studies, cowpea increased nematode infestation [14], while groundnut decreased the population of nematodes [3,15,16]. The biological effects of legumes are complex [17] but our results showed that the N-effect seemed to be the most important factor governing sorghum response to crop rotation. Nitrogen and P are known to be the most limiting factors of Alfisols and Ultisols of West Africa [1,5].…”

“…The quantity and quality (organic N) supplied by the residues of legumes improve soil N, biological properties and availability of other nutrients, leading to better growth and good health for the succeeding sorghum. As reported inprevious work, subsequent cereal yields are usually increased in legume-cereal rotations [3,4,18] as a consequence of mineral N provided by mineralization of legume residues [19][20][21][22] and the improvement of soil biological properties and availability of nutrients [17]. Then, despite the increase of the population of nematodes, the succeeding sorghum benefits from good nutriational conditions and has quicker and better growth, particularly during the first period of the season.…”

“…Nitrogen and P are known to be the most limiting factors of Alfisols and Ultisols of West Africa [1,5]. Legumes can also improve other soil properties such aspH of acid soils, microbial N and fungal biomass in the rhizosphere [17]. In the sensitive rainfed ecosystem of West Africa, the mineral N supplied by legume residues at the start of the season as a basal source of N can explain the good development and yields of sorghum.…”

Nutrient availability and management in the rhizosphere: exploiting genotypic differences

“…P availability had no effect on microbial community composition in the rhizosphere of, for example, Sorghum bicolor (Marschner et al ., 2004b).…”

Assessment of nutrient deficiencies in maize in nutrient omission trials and long-term field experiments in the West African Savanna

“…Other soil chemical properties, such as pH, may also be favourably affected by the cultivation of legumes (Alvey et al 2001;Sanginga 2003;Tian ?tul?> et al 2005). Rotations may affect soil microbial populations, arbuscular mycorrhizae and parasitic nematode populations (Bagayoko et al 2000;Alvey et al 2001Alvey et al , 2003Marschner et al 2004). However, it remains difficult to quantify to what extent changes in soil biota relate to variations in cereal yield.…”