Introduction Rice (Oryza sativa L.)-wheat (Triticum aestivum L.) is one of the world's largest agricultural production systems. Intensive farming techniques, unbalanced application of chemical fertilizers without proper review of soil nutrient status, poor soil management and high-yielding crop varieties have resulted in a substantial decrease in soil organic matter (SOM) and crop productivity over the past decades. [1, 2]. A useful strategy to feed the rapidly growing population is to increase the unit area production by using existing agricultural area and resources [3]. This can be accomplished by growing improved crop varieties [4], site specific way of fertilizer application [5], integrated

A field experiment was conducted 2010 cropping season at the Institute for Agricultural Research Farm, Samaru, (11 0 , 11' N, 07 0 38'E). Experimental site was 686 m above sea level in the northern Guinea savanna ecological zone of Nigeria. Study focused on to assess the effects of poultry manure rates (0, 4, 8 and 12 t ha-1) and seedling age (2, 3 and 4 weeks after sowing) at transplanting on growth and yield of amaranth (Amaranthus caudatus L.). Treatments consisted of factorial combinations of four levels of poultry manure and three transplant ages in a randomized complete block design (RCBD) with three replicates. Results indicated that plant height (cm), shoot fresh weight (kg) and number of leaves and branches per plant were significantly (P<0.05) higher with the application of 8 t ha-1 of poultry manure compared with no-manure than the other treatments. However, in most cases, the difference in growth characters using poultry manure rates varying from 4 to 12 t ha-1 were non-significant. Seedlings transplanted at 4 weeks of age were significant taller with shoot fresh weight than 2-weeks old seedlings at the initial growth stage. Transplant age had no effect on these parameters at later stage. All the other growth parameters were not affected (P<0.05) by transplant age. Study suggested that marketable yield increased significantly with increasing poultry manure (4 t ha-1) with transplanting age (2-3 weeks) after emergence to benefit farmers the highest.

Soil microbial biomass (SMB) is the main driving force in nutrient cycling and good indicator of soil productivity. A greenhouse experiment was designed to assess the effect of soil compaction, cropping system [sole maize, rotation 1 (inoculated soybean-maize), rotation 2 (un-inoculated soybean-maize) and intercrop 1(inoculated soybean-maize)and intercrop 2(un-inoculated soybean-maize)] and nitrogen fertilizeron soil microbial biomass C (SMB-C) and N (SMB-N) and their proportion to soil organic C and total N. SMB-C and SMB-N were higher in un-compacted than compacted soils with percent differences of 2.63 and 6.04% respectively. However, they were 19.32 and 36.36% lower in sole maize compared to rotation 1, 7.83 and 15.36% for rotation 2, 22.19 and 20.06% for intercrop 1 and 14.62 and 12.54% for intercrop 2. The results also showed that the application of 120 kg N ha -1 produced the highest soil microbial biomass as a percent of soil organic carbon, followed by 80 kg N ha -1 , while the least value was obtained under zero application of nitrogen. Microbial biomass carbon and nitrogen as a percent of soil total nitrogen was significantly higher up to 80 kg N ha -1 before it decline at 120 kg N ha -1 suggesting better soil productivity improvement at 80 kg N ha -1 under the cropping systems with inoculated soybean. The findings indicate the need for inoculation in soybean-maize cropping systems to improve soil microbial biomass especially under less soil disturbances.