Emissions of N 2 O were measured after application of NH 4 NO 3 fertilizer and incorporation of winter wheat and rye green manures in two ®eld experiments in southeast England. Incorporation of green manure alone resulted in temporary immobilization of soil N, small N 2 O emissions and also low availability of N for the following crop. Emissions were increased after application of inorganic fertilizer, and were further increased from integrated management treatments whereby green manure residues were incorporated after fertilizer application. The highest emission was from the incorporated winter wheat green manure plus fertilizer treatment, with 1.5 kg N 2 O-N ha ±1 (0.6% of N applied) being emitted over the ®rst 55 days after incorporation. This high emission was attributed to the supply of C in the residues providing the energy for denitri®cation in the presence of large amounts of mineral N and the creation of anaerobic microsites during microbial respiration.

Soil erosion is a multifactor threat to crop production and the environment. Most studies on soil erosion characterization have not focused on soil nutrient loss associated with erosion. The aim of this study was therefore to quantify the magnitude of nutrient loss through soil erosion under different cropping systems and amendments to inform agronomic practices in sub-Saharan Africa (SSA). A field experiment was carried out on runoff plots with different cropping systems (sole maize, sole cowpea, sole maize and maize intercropped with soybean) as main plots and soil amendments (biochar, NPK (Nitrogen +Phosphorus +Potassium) fertilizer, NPK + biochar and a control (no amendment)) constituting the subplots in a randomized complete block design. For each block, a bare plot was included to assess the efficiency of the different crop and soil management practices on soil erosion. The study was carried out in three consecutive cropping seasons in the semi-deciduous forest zone of Ghana. The bare plots had the highest amounts of nitrogen (N), phosphorus (P), and potassium (K) eroded: 33.88, 12.35 and 12.75 kg ha-1 respectively followed by the control plots with magnitude of 20.43, 8.42 and 7.87 kg ha-1 respectively for N, P and K. Sole maize had the highest amounts of nutrient loss: 19.71, 8.12 and 7.27 for N, P and K respectively compared to all the other cropping systems where the losses varied respectively from 12.38 to 17.12, 6.67 to 7.49 and 5.81 to 6.75 kg ha-1 The legume-based cropping systems under inorganic fertilizer and biochar management effectively reduced nutrient loss more than all other treatment combinations. The off-site effect of soil erosion expressed as enrichment ratio (ER) was higher for all plots, which received inorganic fertilizer inputs varying from 1.93 to 3.06 while the other treatments had ERs of 1.51 to 2.03. The ERs of fine soil particles were greater than 1 (ranging from 1.14 to 3.6) being relatively higher than that of coarse particles (sand) with values below 1 (ranging from 0.62 to 0.88). The least cumulative monetary value of nutrient loss (30.82 US$ ha-1) was observed under cowpea cropping system which received NPK + BC treatment. Soil erosion affected directly soil nutrient depletion through nutrient loss; however, integrated soil fertility management associated with legume-based cropping systems can be alternative options to reducing its effects on croplands in SSA.

A field experiment was conducted during the major cropping season of 2014 at the Plantation Section of the Department of Crop and Soil Sciences, Kwame Nkrumah University of Science and Technology, Ghana to evaluate the effect of tillage and different application rates of phosphorus fertilizer on the growth and yield of sweet potato variety Okumkom. The tillage methods are ridge & mound while the different rates of phosphorus fertilizers are 0, 30, 60, 90 and 120 kg P2O5/ha in triple superphosphate (46% P2O5) form. Factorial experiment was used and treatments were arranged in a Randomized Complete Block Design with three replications. All the treatments were supplemented by 30 kg N/ha in the form of Urea (46% N). Results of this study indicated that plant growth was not significantly affected by tillage, but root yield was affected significantly with ridging produced the highest root yield. Further, highest growth and yield was observed from the 60 kg P2O5/ha treatment.

The need to obtain crop varieties that are tolerant to heat and drought cannot be overemphasised especially with the threat of climate change to agricultural productivity in sub-Saharan Africa. Bambara groundnut has been identified as a drought tolerant crop; however, variations exist among landraces with respect to drought tolerance. An experiment was therefore conducted to evaluate the performance of five bambara groundnut landraces: Black eye, Burkina, NAV 4, NAV Red and Tom, to drought and heat stress, at the Irrigation Company of Upper East Region (ICOUR) at Tono-Navrongo in the Upper East Region of Ghana. The experiment was arranged in a Randomized Complete Block Design with three replicates. The heat trial was irrigated once weekly to field capacity until crop maturity. The drought trial was irrigated once weekly until 30 DAS, after which irrigation ceased. Burkina, a landrace from Burkina Faso produced the highest pod yield of 1.2 t/ha under the heat treatment. Tom did not produce any pod yield. Under drought, Burkina exhibited the greatest root dry weight and leaf area at 120 DAS, and had the longest leaf area duration (LAD). Burkina exhibited bunch canopy architecture, while NAV 4, NAV Red, and Black eye had an intermediate canopy type and Tom a spreading type. Burkina proved the most drought and heat tolerant among the five landraces evaluated. Though a drought tolerant crop, temperatures beyond 38°C and low relative humidity can negatively affect pod yield of bambara groundnut even when irrigation is provided. It is important to test the performance of a crop under a new environment before money is invested into its production in that environment.

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Soil erosion is a major constraint to crop production on smallholder arable lands in Sub‐Saharan Africa (SSA). Although different agronomic and mechanical measures have been proposed to minimize soil loss in the region and elsewhere, soil management practices involving biochar‐inorganic inputs interactions under common cropping systems within the framework of climate‐smart agriculture, have been little studied. This study aimed to assess the effect of different soil and crop management practices on soil loss characteristics under selected cropping systems, typical of the sub‐region. A two‐factor field experiment was conducted on run‐off plots under different soil amendments over three consecutive cropping seasons in the semi‐deciduous forest zone of Ghana. The treatments, consisting of three soil amendments (inorganic fertilizer, biochar, inorganic fertilizer + biochar and control) and four cropping systems (maize, soyabean, cowpea, maize intercropped with soyabean) constituted the sub‐plot and main plot factors, respectively. A bare plot was included as a soil erosion check. Seasonal soil loss was greater on the bare plots, which ranged from 9.75–14.5 Mg ha−1. For individual crops grown alone, soil loss was 31%–40% less under cowpea than under maize. The soil management options, in addition to their direct role in plant nutrition, contributed to significant (p < 0.05) reductions in soil loss. The least soil loss (1.23–2.66 Mg ha−1) was observed under NPK fertilizer + biochar treatment (NPK + BC) over the three consecutive cropping seasons. Biochar in combination with NPK fertilizer improved soil moisture content under cowpea crops and produced considerably smaller bulk density values than most other treatments. The NPK + BC consistently outperformed the separate mineral fertilizer and biochar treatments in biomass yield under all cropping systems. Biochar associated with inorganic fertilizers gave economic returns with value–cost ratio (VCR) > 2 under soyabean cropping system but had VCR < 2 under all other cropping systems. The study showed that biochar/NPK interactions could be exploited in minimizing soil loss from arable lands in SSA.

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