The impacts of crop rotation and inorganic nitrogen fertilization on soil microbial biomass C (SMBC) and N (SMBN) and water-soluble organic C (WSOC) were studied in a Guinea savanna Alfisol of Nigeria. In 2001, fields of grain legumes (soybean and cowpea), herbaceous legume (Centrosema pascuorum) and a natural fallow were established. In 2002, maize was planted with N fertilizer rates of 0, 20, 40 and 60 kg N ha )1 in a split-plot arrangement fitted to a randomized complete block design with legumes and fallow as main plots and N fertilizer levels as subplots. Surface soil samples were taken at 4 weeks after planting and tasselling stage of the maize. Inorganic N fertilization had no significant (P>0.05) effect on SMBC, SMBN and WSOC, while crop rotation significantly (P<0.0001) affected both SMBC and WSOC. These results demonstrate that crop rotation do not necessarily influence the gross soil microbial biomass, but may affect physiologically distinct subcomponent of the microbial biomass. The soils under the various rotations had a predominance of fungi community as indicated by their wide biomass C/N ratio ranging from 9.2 to 20.9 suggesting fungi to be mainly responsible for decomposition in these soils. Soil microbial biomass and WSOC showed significant (P<0.05) correlation with both soil pH and organic carbon but no relationship with total N. Based on these results, it appears that the soil pH and organic carbon determined the flux of the soil microbial biomass and amount of WSOC in these soils.

Striga possesses an ominous obstacle to the African continent that is struggling with food security as it affects the livelihood of more than 300 million people. The control of Striga has proved exceptionally difficult. Two fallows, namely natural fallow (NF) and A. histrix fallow (AF) were maintained in 2012, such that the field was divided into two parts and each part was further divided into three replicates. Each part was separated from one another by a strip of 2 m width and the fallow factor was randomly assigned to each part which constituted the main plot. In 2013, the inorganic N fertilizer levels (0, 60, 90 and 120 kg ha-1) were applied to the fallow plots and assigned to the sub-plot. These treatments were laid out in a split plot arrangement fitted to a randomized complete block design with three replicates. The two fallows significantly (P < 0.05) reduced Striga infestation similar to application of N at 60 – 120 kg N ha-1. The two fallows significantly (P< 0.05) increased SOC. Only natural fallow significantly (P<0.05) increased the STN by 36 %. Maize grain yield after natural fallow (1527 kg ha-1) was not significantly (P>0.05) different from that after A. histrix (1943 kg ha-1). Inorganic N application had highly significant (P<0.05) effect on grain yield. Lowest grain yield of 1253 kg ha-1 was obtained without inorganic N application, which was significantly different from those fertilized with inorganic N. Inorganic N fertilizer rate of 60 kg ha-1 seems to be optimum for maize. The Nitrogen Fertilizer Replacement Value of A. histrix was low, 13 kg N ha-1. The effect of both fallows on grain yield was due mainly to increased SOC content.

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The distribution of various forms of phosphorus was evaluated along a toposequence located in an Alfisol in Teaching and