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Crop residue management strategies must be adapted for improving carbon (C) balance and soil C stock in agroecosystems in sub‐Saharan Africa with consideration of the crop residue availability and site‐specific soil characteristics. We conducted field experiments to determine the effects of crop residue application method (incorporation/mulching) and quality (maize/cowpea) and N fertilizer application on the soil respiration rate and soil C stock in the surface soil layer (0–15 cm) in maize croplands with contrasting soil textures (clay/sandy) over 2 years from 2012 to 2014 in Tanzania. At the clay site, the incorporation of maize residues showed a 38% increase in CO2 flux compared to mulching, whereas, at the sandy site, mulching showed a 16% increase compared to the incorporation. At the sandy site, mulching practice retained soil moisture content and apparently enhanced the decomposition of the original soil organic C in the surface layer. It is, therefore, suggested that mulching practice may accelerate a long‐term depletion of soil C stock at the sandy site. The cowpea residue incorporation led to rapid decomposition because of its high biodegradability at both sites. The N fertilizer application stimulated the decomposition of labile soil organic matter. The soil C stock in the surface layer did not significantly change after the 2‐year experiment, irrespective of crop residue treatment and soil type. In conclusion, adequate crop residue management in terms of suppressing CO2 flux during a cropping season depends on soil type, but the long‐term effect on soil C stock is unclear. [ABSTRACT FROM AUTHOR]

Soil phosphorus (P) forms have been practically defined as chemically fractionated pools. A knowledge of the abundance and diversity of P forms in soil, and the factors affecting them, will lead to better soil management. However, little is known about the differences in P forms among soils with different geological properties in tropical Africa. The aim of this study was to investigate the P forms in soils with different physicochemical properties formed under different geological conditions in southern Tanzania and to identify the factors affecting the P forms in these soils. In total, 37 surface soil samples were collected from three geological groups; the plutonic (mainly granite) rock (PL) group, the sedimentary and metamorphic rock (SM) group, and the volcanic ash (V) group. Soil P was sequentially extracted by NH4Cl, NH4F, NaHCO3, NaOH + NaCl, and HCl, and inorganic (Pi) and organic P (Po) in each fraction were determined. The lowest total P was in the PL group (average, 360 mg P kg-1) because of the high sand content. Iron (Fe)-P (NaOH-Pi) was the major form in this group, accounting for 8.4% of total P. In the SM group (average total P, 860 mg P kg-1), Fe-P was the major form in most, accounting for 7.8% of total P. Soils in the SM group occasionally had high calcium (Ca)-P due to application of chemical fertilizer at the collection site. The V group had the highest total P (average, 1600 mg P kg-1) and its major P form was Ca-P, which was possibly derived from primary minerals (i.e., apatite), accounting for 14% of total P. In addition, the high oxalate-extractable Al possibly caused the accumulation of Al-P in the V group. Oxalate-extractable Fe generally increased with increasing Fe-Pi, while oxalate-extractable Al increased with increasing organic P and Al-Pi in soils in all three geological groups. These results demonstrate that the soil P forms differ greatly among sites in southern Tanzania with different geological conditions and associated soil properties. [ABSTRACT FROM AUTHOR]

Abstract: Phosphorus deficiency is one of the largest constraints to crop production in tropical African soils owing to low native soil P and the high P fixation capacity of highly weathered soils. To achieve better soil P management, it is necessary to evaluate the effects of land management on soil P dynamics and P budget. We conducted a 4-year cultivation experiment in two dry tropical croplands in Tanzania at two sites with contrasting soil textures, viz. clayey and sandy. We then evaluated the effect of different types of land management (control plot, plot treated with crop residue only, plot treated with fertilizer only, and plot treated with both crop residue and fertilizer) on soil fractionated P and P budget at both sites. At the end of the experiment, fertilizer application (50kgPha−1 year−1) clearly increased NaOH-extractable inorganic P by 66.0–82.6kgPha−1 (soil depth 0–15cm) at the clayey site and was equivalent to 33.0–41.3% of applied P fertilizer. However, fertilizer application did not clearly increase NaOH-extractable inorganic P at the sandy site owing to its low content of Al and Fe oxides. On the other hand, the effect of crop residue application (7.5MgCha−1 year−1) on fractionated soil P was scarce, even with fertilizer application. Thus, applied crop residue increased soil C but did not significantly increase any P fractions, even with substantial P fertilization. On the basis of the P budget, we found that P was substantially unaccounted for only in the fertilizer treatment plots, i.e., 59.5–89.1 and 121.3–138.2kgPha−1 (soil depth 0–15cm) at clayey and sandy sites, respectively. Our results indicate that substantial P loss, possibly through leaching, seemed to have occurred at the sandy site in particular. Therefore, not only P fixation but also P loss from leaching of applied P should be reduced to achieve better P management in this region. [Copyright &y& Elsevier]

The members of the Editorial Board and management staffs of Soil Science and Plant Nutrition express their deep appreciation to the scientists listed below who reviewed the manuscripts submitted for publication from October 2021 until September 2022. Their critical comments and helpful suggestions have certainly contributed to the enhancement of the quality of articles published by the journal. [Extracted from the article]