Phosphorus sorption capacity in relation to soil properties in profiles of sandy soils of the Keta sandspit in Ghana

The sandy soils of Anloga in the Volta region form part of the Keta basin. The soils are infertile and of low productivity but are intensively cultivated for vegetables such as shallot (Allium cepa).  Farmers have augmented the fertility of the soils by adding cow dung and poultry manure for the past seventy years. To study the P dynamics in the soils, three profiles were dug on cultivated (F) and two on uncultivated (U) fields to study P accumulation and sorption after decades of cultivation. The results showed that total P content was 533 mg P kg-1 at the depth of 50cm and below in the F-profiles compared to 416 mg P kg-1 of similar depthof the uncultivated soils, suggesting some movement of P from the surface soil into the subsoil. The maximum P sorption capacity of the U soils was low (92 6 mg kg-1) but higher than those of the F soils (58.8 mg P kg-1). Multiple regression analyses showed that pH and Ca were the two major determinants of P sorption in the soils. The degree of P saturation (DPS) of the surface soils of the cultivated soils was higher than the average critical value of 25% DPS of an arable land but in the lower depths of the cultivated soils, the DPS decreased tremendously below the critical level of 25% which meant that these depths were not saturated well enough to enhance leaching of P to the underground waters

Long-Term Cropping Effect on Phosphorus Fractions in an Ultisol of the Humid Forest Zone in West Africa

The nature of phosphorus (P) pools in soils after application of P fertilizers should be considered when designing management practices to raise P fertility. Five rates of P: 0(P0), 45(P45), 90(P90), 135(P135) and 180(P180) kg ha−1 in the form of triple superphosphate (TSP) were applied once in 1993 on a Typic Paleudult at Man in Côte d'Iviore and the soil was cropped successively for five years (i.e., up to 1998) with four upland rice cultivators. At the end of the cropping season in 1998, soil samples were collected from the various P treated plots and the following P fractions were analyzed: resin-P, NaHCO3-Pi, NaOH-Pi, HCl-P residual P and organic P. The P fractions were compared with those of stored soil samples collected in the field before the initiation of the experiment in 1993. Five years of cropping the soil reduced labile Pi (resin-P+NaHCO3-Pi) from 10.8 mg P kg−1 in the uncultivated soil to 7.62 mg P kg−1 in the control (P0) and to 9.71 mg kg−1 in the P45 treatment. Labile Pi in P90 was the same (10.7 mg P kg−1) as in the uncultivated soil but in the P135 and P180 soils, labile Pi increased by 1.3 and 2.7 mg P kg−1 above that of the uncultivated one. The NaOH-Pi and residual P fractions of lower availability increased with increasing rates of P application. The results suggested that on the Ultisol studied, P applied once to a field, cropped successively over a period of time was not an adequate management option. Frequent P application at low rates at each cropping season is suggested and merits investigation on the Ultisol studied

Phosphate retention and extractability in soils of the humid zone in West Africa

Phosphate adsorption and desorption studies provide insight for developing P management strategies. Very few studies have concentrated on P desorption which provides information on the reversibility of adsorbed P. Phosphate adsorption and desorption studies were carried out on seven rice-growing soils from three countries in West Africa, with the objective of relating these processes to P management strategies for the soils. The standard P requirement (SPR) of soils, defined as the amount of P to be added to attain an equilibrium solution concentration of 0.2 mg P l−1, varied from 42 to 175 mg P kg−1. Out of the seven soils, four required low amounts and the other three needed relatively higher P applications. The extractability of the adsorbed P in different extractants was: 0.01 M KCl 32–78%, Olsen P 21–112%, and Bray 1 P 15–40%. Differences in the amounts of P desorbed by the soils suggested that the critical P levels needed for P management must be different. Management options to increase P availability in the soils are suggested

Assessing the Effect of Seedling Age and Time of Urea Supergranule Application on Rice Growth, Yield and Nitrogen Use efficiency

Nitrogen is the most limiting nutrient in tropical soils and nitrogen fertilizer application to rice is subject to losses. Good synchrony of nitrogen availability to crop’s need is a strategy to reduce losses and improve efficiency. A pot experiment was conducted to assess the effect of seedling age and time of urea supergranule application on rice growth, yield and nitrogen use efficiency. The experiment consisted of 10, 14, 21 and 28-day old seedlings and urea supergranule applied at 0, 7, 14 and 21 days after transplanting with a check treatment without nitrogen application. Results indicated significant effect of seedling age on growth, yield and nitrogen use efficiency. Highest grain yield, nitrogen uptake, agronomic use efficiency of nitrogen and nitrogen recovery efficiency were obtained with 10 and 14-day old seedlings, while the lowest values were observed for 28-day old seedlings. Urea supergranule applied at 7 or 14 days after transplanting gave the highest rice growth parameters while the lowest performances were obtained with urea supergranule applied at 0 and 21 days after transplanting. The interactive effect showed better growth, yield and nitrogen use efficiency of rice when urea supergranule was applied at 7 or 14 days after transplanting seedlings of 10 and 14-day old. The results suggested that even though application of urea supergranule at 7 and 14 days after transplanting increased rice yield over 0 and 21 days after transplanting, for the aged seedlings of 21 and 28-day old, the variation of urea supergranule application time could not compensate for the decrease of yield due to old seedlings transplanting

Phosphorus adsorption, rice dry matter yield, and P use efficiency as influenced by phosphorus fertilizer rates in rainfed lowland soils in Togo

The study focused on improving phosphorus (P) fertilizer recommendation in rainfed lowland rice soils in Togo. Phosphorus adsorption was conducted on four soils to determine their P adsorption characteristics and standard phosphorus requirement (SPR). The adsorption maximum ranged from 143 to 200 mg P/kg. The amount of P adsorbed range from 62.70 to 74.85 mg P/kg. Greenhouse experiment was conducted to determine rice response to phosphorus rates based on the SPR values, and to assess rice P uptake and use efficiency. Five phosphorus rates, Control: 0 mg P kg−1, P recommended rate (RR): 5 mg P kg−1, 4 × RR: 20 mg P kg−1, 50% SPR and 100% SPR were used. Results indicated no significant difference between the Control treatment and the P recommended rate (RR), and between the 50% SPR and the 100% SPR with reference to shoot dry matter yield. P uptake and P use efficiency were significantly and positively influenced by the various P fertilizer rates. From the study, the blanket P recommended rate is inappropriate, however, site-specific P fertilizer rate of 50% SPR may be recommended to improve rainfed lowland rice yields in Togo

Sustainable P-enriched biochar-compost production: harnessing the prospects of maize stover and groundnut husk in Ghana’s Guinea Savanna

Farmers in resource-poor areas of the Guinea Savanna zone of Ghana often face declining soil fertility due to the continuous removal of nutrient-rich harvested produce from their fields. This study focuses on the Lawra Municipality in the Guinea Savanna zone of Ghana, where low soil fertility, specifically, limits phosphorus (P) bioavailability and hinders crop production. The objective of this research is to formulate P-enhanced biochar-compost from maize stover (MS) and groundnut husk, which abound in the area, to close the nutrient loop. MS was co-composted with groundnut husk biochar at varying rates of 0, 10, 20, 30, and 40% by volume. To facilitate decomposition using the windrow system, the composting heaps were inoculated with decomposing cow dung, and the moisture content was kept at 60% throughout the monitoring period. The addition of biochar shortened the lag phase of composting. However, rates above 20% resulted in reduced degradation of MS. Biochar incorporation enriched the available phosphorus content in the final compost from 286.7 mg kg−1 in the non-biochar-compost to 320, 370, 546, and 840.0 mg kg−1 in the 10, 20, 30, and 40% biochar-compost, respectively

Application of inorganic phosphorus fertilizer

Phosphorus deficiency has been identified as a major constraint to crop production on highly weathered, low activity clay soils in the humid and subhumid zones of sub-Saha-ran Africa. Phosphorus deficiency is further accentuated on many of the soils, especially Ul-tisols and Oxisols, because of fast reversion of soluble P into insoluble forms through reactions with iron and aluminum oxides. Phosphorus fertilization is of fundamental importance for sustaining crop production, maintaining soil fertility, and enhancing the fertility of degraded soils. Recent research indicates that the application of inorganic P through soluble and relatively reactive phosphate rock (PR) sources can be effective in increasing crop production and productivity, enhancing the replenishment of N through biological fixation, and in the maintenance of improvement of the overall fertility of soils. The effectiveness of PR and the residual value of fertilizer P from soluble and rock P sources can be enhanced by amending them with locally available organic and crop residues or by the recycling of P from rock RP through leguminous crops. It is suggested that an approach in which the use of P-efficient genotypes and P management are integrated is more practical and sustainable

DataSheet1_Sustainable P-enriched biochar-compost production: harnessing the prospects of maize stover and groundnut husk in Ghana’s Guinea Savanna.docx

Farmers in resource-poor areas of the Guinea Savanna zone of Ghana often face declining soil fertility due to the continuous removal of nutrient-rich harvested produce from their fields. This study focuses on the Lawra Municipality in the Guinea Savanna zone of Ghana, where low soil fertility, specifically, limits phosphorus (P) bioavailability and hinders crop production. The objective of this research is to formulate P-enhanced biochar-compost from maize stover (MS) and groundnut husk, which abound in the area, to close the nutrient loop. MS was co-composted with groundnut husk biochar at varying rates of 0, 10, 20, 30, and 40% by volume. To facilitate decomposition using the windrow system, the composting heaps were inoculated with decomposing cow dung, and the moisture content was kept at 60% throughout the monitoring period. The addition of biochar shortened the lag phase of composting. However, rates above 20% resulted in reduced degradation of MS. Biochar incorporation enriched the available phosphorus content in the final compost from 286.7 mg kg−1 in the non-biochar-compost to 320, 370, 546, and 840.0 mg kg−1 in the 10, 20, 30, and 40% biochar-compost, respectively.</p