Inclusion of legumes in cropping systems is essential for sustainable management of farming systems and reducing the nitrogen (N) fertilizer requirement for maize production. The study evaluated the effect of growing legumes (soybean, cowpea and velvet bean) and maize the same year in rotation, on maize yield and soil fertility indices. The agronomic practices implemented were residue management (residue added and residue removed) and fertilizer N application (0 kg N ha −1 and 60 kg N ha −1 ) under four rotation systems. The result showed that growing velvet bean the same year in rotation with maize was effective in increasing maize yield and improving some soil fertility indices over growing maize after maize the same year in the same location. Compared to maize monocropping, over 100% increase in maize yield was obtained with velvet bean-maize rotation even in absence of residue incorporation. In addition, velvet bean-maize rotation increased maize yield over cowpea- and soybean- maize rotations. The rotation effect occurred as a result of improvement in soil nitrogen, avail phosphorus (P), exchangeable magnesium (exch Mg) and effective cation exchange capacity (ECEC). Grain legumes-maize rotations equally increased maize yield over sole maize. Generally legume-maize rotations increased total N, avail P, exch K, Mg and effective cation exchange capacity over sole maize. Crop residue incorporation and N fertilizer application significantly improved soil N and maize grain yield (0.18%, 2.74 tha −1 in 2008; 0.22%, 1.16 tha −1 in 2009 and 0.19%, 2.72 tha −1 in 2008; 1.35 tha −1 in 2009 respectively) over non-residue incorporation (0.16% and 1.84 tha −1 in 2008, 0.66 tha −1 in 2009) and zero N application (0.16% and 1.83 tha −1 in 2008 and 0.17% and 0.85 tha −1 in 2009). Therefore, velvet bean could be planted the same season with subsequent maize in rotation cropping for intensive sustainable maize production in sandy-loam soils without fertilizer N. For grain legumes such as soybean and cowpea to be effective in rotation cropping with maize, the grain legumes have to be planted early before the full set of rain because excess rain would affect their growth and development.

Core Ideas N–P–K fertilizer microdosing increased maize yields by 99% in the humid forest zone. Gleyic Plinthic Acrisol produced higher maize grain yield than the Plinthic Acrisol. Microdosing increased N, P, and K use efficiency of maize in rotation vs. sole cropping. Maize grain yield and net returns were optimal with N20P40K20 and N0P40K20 microdoses. High fertilizer costs pose a challenge in smallholder farming; optimizing fertilizer recommendations that are affordable to resource‐poor farmers could increase crop yield and income. The study aimed to determining the yield and economic effects of N–P–K fertilizer microdosing on maize (Zea mays L.) crops on Gleyic Plinthic Acrisol (GPA) and Plinthic Acrisol (PA) in the semideciduous rainforest zone of Ghana using a split‐plot randomized complete block design with three replications. The field trial included two cropping systems (continuous maize cropping [CMC] and cowpea [Vigna unguiculata (L.) Walp.]–maize rotation [CMR]) as main plots with four treatments (N0P0K0, N0P20K20, N0P40K20, and N20P40K20) and the recommended fertilizer rate (N90P60K60) as subplots. Fertilizer treatment effects on maize stover and grain yields were assessed. The microdose treatments increased maize yields by 32 to 99% across cropping systems and soil types. Maize grain yield increase was higher on the GPA than on the PA. The N90P60K60 and N20P40K20 treatments resulted in higher grain and stover yields than the other treatments across cropping systems and soil types. Among the treatments maximum grain yield increases of 76 and 99% were obtained with N20P40K20 on the PA and the GPA, respectively, under CMC. Under CMR, grain yield increased by 46% with N0P40K20 (PA) and 74% with N0P20K20 (GPA). The largest net return was obtained with N20P40K20 under CMC across both soil types and with N0P20K20 (GPA) and N0P40K20 (PA) under CMR. These fertilizer microdoses can be considered appropriate for increasing maize yield and the income of smallholder farmers.

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This study aims to investigate soil organic carbon (SOC) and total nitrogen (TN) contents and stocks, CO2 emissions and selected soil properties in croplands, grazing lands, exclosures and forest lands of semi-arid Ethiopia. Sampling was done at 0–30, 30–60 and 60–90 cm soil depths and concentration and stocks of SOC, TN and selected soil properties were determined using standard routine laboratory procedures. There were variations in distribution of SOC and TN stock over 90 cm depth across land use types and locations, decreasing from topsoils to subsoil, with average values ranging from 48.68 Mg C ha−1 and 4.80 Mg N ha−1 in Hugumburda cropland to 303.53 Mg C ha−1 and 24.99 Mg N ha−1 in Desa’a forest respectively. Forest sequestered significant higher SOC and TN stock, decreasing with depth, compared with other land use types. In Desa'a and Hugumburda, the conversion of forest to cropland resulted in a total loss of SOC stock of 9.04 Mg C ha−1 and 2.05 Mg C ha−1, respectively, and an increase in CO2 emission of 33.16 Mg C ha−1 and 7.52 Mg C ha−1 yr−1, respectively. The establishment of 10 years (Geregera) and 6 years (Haikihelet) exclosures on degraded grazing land increased SOC stock by 13% and 37% respectively.

Soil organic carbon (SOC) and total soil nitrogen (TSN) dynamics have both pedological and agronomic basis. Knowledge of their retention within aggregate hierarchies of varying soil textures as influenced by land use change is limited. The capacity of loam (L), clay loam (CL), sandy loam (SL) and sandy clay loam (SCL) soils to retain SOC and TSN in water-stable aggregate (WSA) at 10-cm intervals of 0-30 cm topsoil depths under cultivated and bushfallow/ uncultivated systems was investigated. The soils showed high dispersion ratio and great variations in aggregate silt and clay indices (CL > L > SCL > SL) under both land uses. Across soil depths, the uncultivated CL, SL and SCL soils had moderate to high > 2.00 mm WSA whose reduction due to cultivation impact was more pronounced in SL than in CL soil. Across soil depths and land uses, SOC content seemed higher in the macro- (> 0.50 mm) than in the micro- (< 0.50 mm) aggregates of all the soils while the reverse marked aggregate TSN content in almost all the soils. Cultivation mostly reduced macro-aggregate-associated SOC and TSN in L > CL > SL and in L > SL > CL > SCL soils, respectively. However, cultivation showed no reduction influence on micro-aggregate-associated SOC of all the soils. Cultivation-related reduction in micro-aggregate-associated TSN was more pronounced in the generally more ‘clayey’ CL and SCL than the L and SL soils. So, the potential of bush-fallowing to enhance micro-aggregateassociated TSN storage and stabilization against adverse influence of cultivation depends on soil texture.