Soil organic carbon (SOC) management for sustainable productivity of cropping and agro-forestry systems in Eastern and Southern Africa

In Eastern and Southern Africa, the shifting from the no-external input agriculture (shifting cultivation through slash and burn) to intensified agricultural systems has resulted in widespread agro-ecosystems with high soil organic carbon and nutrient depletion. This is quite evident in farming systems with reduced fallow period or those that practice continuous cropping without or with little inputs. Long-term experiments indicate that losses of up to 0.69 t carbon ha⁻¹ yr⁻¹ in the soil surface layers are common. Such losses are commonly reported by farmers engaged in participatory community-based research development projects. This calls for judicious strategies for recapitalization or replacement of these depletions. Such strategies include direct SOC replenishment through addition of organic materials, notably manures, wastes, residues and plant litter; biomass transfer; incorporation of improved fallows in the farming systems. Indirect contribution to SOM replenishment or recapitalization may be achieved through inorganic fertilizations and amendments; legume integration in the production system; and combined inorganic and organic inputs. Research is required to identify inputs that help meet both nutrients availability while contributing to SOC build up at the same time. This revised version was published online in June 2006 with corrections to the Cover Date.     

Integrated soil management for the savanna zone of W. Africa: legume rotation and fertilizer N

Integrated soil management with leguminous cover crops was studied at two sites in the northern Guinea savanna zone of northern Nigeria, Kaduna (190 day growing season) and Bauchi (150 days). One-year planted fallows of mucuna, lablab, and crotalaria were compared with natural grass fallow and cowpea controls. All treatments were followed by a maize test crop in the second year with 0, 30, or 60 kg N ha^–1 as urea. Above ground legume residues were not incorporated into the soil and most residues were burned early in the dry season at the Kaduna site. Legume rotation increased soil total N, maize growth in greenhouse pots, and dry matter and N accumulation of maize. Response of maize grain yield to 30 kg N ha^–1 as urea was highly significant at both sites and much greater than the response to legume rotation. The mean N fertilizer replacement value from legume rotation was 14 kg N ha^–1 at Kaduna and 6 kg N ha^–1 at Bauchi. W ith no N applied to the maize test crop, maize grain yield following legume fallow was 365 kg ha^–1 higher than natural fallow at Bauchi and 235 kg ha^–1 higher at Kaduna. The benefit of specific legume fallows to subsequent maize was mostly related to above ground N of the previous legume at Bauchi, where residues were protected from fire and grazing. At Kaduna, where fallow vegetation was burned, maize yield was related to estimated below ground N. The results show that legume rotation alone results in small maize yield increases in the dry savanna zone.     

Characterization of microbial communities in a fluidized-pellet-bed bioreactor for wastewater treatment

In order to make clear the microbiological characteristics of the fluidized-pellet-bed bioreactor (FPB) which is a newly developed wastewater treatment device to perform coagulation, particle pelletization, biological degradation and solid-liquid separation in a single unit, the method of denaturing gradient gel electrophoresis (DGGE) was applied in this study paying attention to the microbial diversity of the granular sludge. Spread plate method was also used for enumeration of aerobic bacteria in unit weight of granular sludge. As a result, slight difference was found between the total aerobic bacteria at the bottom, middle, and top sections though the dissolved oxygen (DO) concentration decreased from about 3.5 mg/L at the bottom inlet to 0.23 mg/L at the top of the FPB bioreactor. From the DGGE finger printing, 17 common species were identified from all these sections, and certain specific species were also identified from each section. The comparability of the microbial communities in the three sections was 83.1%, indicating a very stable structure of the microbial communities. The 16 S rRNA sequence analysis results revealed that the 18 operational taxonomic units (OTUs) obtained all belong to Eubacteria. Among them 11 are Proteobacteria, 3 are Actinobacteria, 2 are low G + C gram-positive bacteria and the remaining 2 belong to other bacteria branches. The dominant microbial communities are typical aerobes or facultative anaerobes commonly encountered in conventional activated sludge.     

Sintering and characterisation of ceramics containing paper sludge, glass cullet and different types of clayey materials

The present paper reports on the sintering behaviour of several ceramics prepared using a previously selected mixture of incinerated paper mill sludge and glass cullet in the ratio 60/40 which was blended with 10, 20, 30 and 40 wt.% of three different natural materials. The three natural products were: a red quartzitic clay, a yellow quartzitic clay and a kaolin. All mixtures were blended by attrition milling and dried; powders were sieved, pressed into specimens and fired for 1 h at temperatures ranging from 1040 to 1140 °C. The resulting materials were characterized by water absorption, shrinkage, crystallographic composition, microstructure and physico-mechanical properties. It was observed that materials containing kaolin display the best overall behaviour independently of the quantity of kaolin introduced. Conversely the optimal sintering temperature, and consequently the best properties of the materials prepared using red or yellow clay were measured on products fired at temperatures above 1080 °C; materials and temperatures are affected by the amount of clay added.     

Evaluation of relationship between biogas production and microbial communities in anaerobic co-digestion

Anaerobic co-digestion (ACD) has been used to treat various organic wastes because nutrient balance in the feed can be improved by mixing different organics. Until now, the correlation between characteristics of feedstocks and biogas production by ACD has been studied mainly in terms of biochemical methane potential. It has been rarely tried to understand the co-digestion process in terms of microbial community development. This study aimed to evaluate the performance of batch anaerobic digestion (AD) reactors fed with activated sludge (AS), swine slurry (SS) and food waste (FW) individually or in a mixture of the three wastes (FW: SS : AS=1 : 3 : 2). The AD reactors fed with the mixture showed better performance than those fed with a single substrate. Microbial communities of the batch AD reactors fed with a single substrate or the mixture were analyzed and the result was related to the performance of the AD reactors.     

Soil phosphorus pools and cycling as affected by changing land-uses in a semi-steppe ecosystem

Nutrient Cycling in Agroecosystems - Land-use changes in native rangelands can greatly affect nutrient cycling processes. While phosphorus (P) is the second most important macronutrient that limits...     

Fertility status of soils of the derived savanna and northern guinea savanna and response to major plant nutrients, as influenced by soil type and land use management

Although the fertility status of soils in the West African moist savanna is generally believed to be low, crop yields on farmers' fields vary widely from virtually nil to values near the potential production. The soil fertility status was evaluated for a number of farmers' fields selected at random in 2 villages (Zouzouvou and Eglimé) representative for the derived savanna (DS) benchmark area and in 2 villages (Danayamaka and Kayawa) representative for the Northern Guinea savanna (NGS) benchmark area. The relation between soil fertility status and soil type characteristics and fertilizer use was explored. In an accompanying missing nutrient greenhouse trial, the most limiting nutrients for maize growth were determined. While soils in the DS villages were formed on different geological units, soils in the NGS villages could be differentiated according to their position on the landscape. Generally, soils in the DS contained a smaller amount of silt (104 vs. 288 g kg^–1), a larger amount of sand (785 vs. 584 g kg^–1), C (9.3 vs. 6.3 g kg^–1), N (0.7 vs. 0.5 g kg^–1), Olsen-P (10.7 vs. 5.4 mg kg^–1), and had a higher CEC (7.0 vs. 4.8 cmolc kg^–1) than soils in the NGS villages. The large silt content of the soils in the NGS is a reflection of the aeolian origin of the parent material. Within the benchmark areas, general soil fertility characteristics were similar in the villages in the NGS, except for a larger amount of particulate organic matter in Kayawa than in Danayamaka. This may also have led to a significantly larger amount of ammonium-N content in the 0–20 and 20–40 cm soil layers in Kayawa compared to Danayamaka (42 vs 24 kg N ha^–1 in the 0–20 cm soil layer). Differences in topsoil soil characteristics between the DS villages were a reflection of differences in clay quality (kaolinitic vs. 2:1 clay minerals) of the parent material and past fertilizer use. The Olsen-P and exchangeable K contents were observed to increase with increased fertilizer application rate in both benchmarks, while fertilizer application rate had no significant effect on the organic C or total N content of the soil nor on its ECEC. The response of maize shoot biomass production to applied N was similar for both benchmarks (biomass accumulation in the treatment without N was, on average, 55% of the biomass production in the treatment which received all nutrients), while soils in the NGS responded more strongly to applied P than soils in the DS (37% vs 66% of biomass production in the treatment which received all nutrients). The more favourable P status of soils in Eglimé (DS) was attributed to the more intense use of P fertilizers, as a result of government-supported cotton production schemes. Response to cations, S or micronutrients were neglegible. A significant linear relationship was found between the soil Olsen-P content and the response to applied P up to levels of 12 mg kg^–1 in the topsoil. Above this level, a plateau was reached.     

The roles of nitrogen,phosphorus and Potassium in the production of sugarcane in South Africa

The amounts of N and K fertilizers used in the South African sugar industry have increased dramatically in the past four decades, due partly to an increase in the area under sugarcane but also to large increases in the amounts of N and K fertilizers applied per hectare. There has also been an increase in the amount of P fertilizer used but this has been more gradual. The main fertilizer carriers for cane and their relative efficiency are discussed. During this period there has been considerable research into the nutrient requirements of sugarcane. Correlations established between soil and leaf analysis and crop responses to N, P and K fertilizers, and their effects on cane quality, are reviewed. While fertilizer recommendations based on soil and leaf analysis have provided a useful guide for determining the nutrient requirements of cane, they are continually being modified in the light of current research.     

Nitrogen use efficiency by maize as affected by a mucuna short fallow and P application in the coastal savanna of West Africa

Maize is the primary food crop grown by farmers in the coastal savanna region of Togo and Benin on degraded (rhodic ferralsols), low in soil K-supplying capacity, and non-degraded (plinthic acrisols) soils. Agronomic trials were conducted during 1999–2002 in southern Togo on both soil types to investigate the impact of N and P fertilization and the introduction of a mucuna short fallow (MSF) on yield, indigenous N supply of the soil, N recovery fraction and internal efficiency of maize. In all plots, an annual basal dose of 100 kg K ha^–1 was applied to the maize crop. Maize and mucuna crop residues were incorporated into the soil during land preparation. Treatment yields were primarily below 80% of CERES-MAIZE simulated weather-defined maize yield potentials, indicating that nutrients were more limiting than weather conditions. On degraded soil (DS), maize yields increased from 0.4 t ha^–1 to 2.8 t ha^–1 from 1999 to 2001, without N or P application, in the absence of MSF, with annual K application and incorporation of maize crop residues. Application of N and P mineral fertilizer resulted in yield gains of 1–1.5 t ha^–1. With MSF, additional yield gains of between 0.5 and 1.0 t ha^–1 were obtained at low N application rates. N supply of the soil increased from 10 to 42 kg ha^–1 from 1999 to 2001 and to 58 kg N ha^–1 with MSF. Application of P resulted in significant improvements in N recovery fraction, and greatest gains were obtained with MSF and P application. MSF did not significantly affect internal N efficiency, which averaged 45 kg grain (kg N uptake)^–1. On non-degraded soils (NDS) and without N or P application, in the absence of MSF, maize yields were about 3 t ha^–1 from 1999 to 2001, with N supply of the soil ranging from 55 to 110 kg N ha^–1. Application of 40 kg P ha^–1 alone resulted in significant maize yield gains of between 1.0 (1999) and 1.5 (2001) t ha^–1. Inclusion of MSF did not significantly improve maize yields and even reduced N recovery fraction as determined in the third cropping year (2001). Results illustrate the importance of site-specific integrated soil fertility management recommendations for the southern regions of Togo and Benin that consider indigenous soil nutrient-supplying capacity and yield potential. On DS, the main nutrients limiting maize growth were N and probably K. On NDS, nutrients limiting growth were mainly N and P. Even on DS rapid gains in productivity can be obtained, with MSF serving as a means to allow farmers with limited financial means to restore the fertility of such soils. MSF cannot be recommended on relatively fertile NDS.     

Comparison of net ecosystem CO2 exchange in cropland and grassland with an automated closed chamber system

Field measurements of net ecosystem CO₂ exchange (NEE) with high temporal resolution are essential to construct a meaningful ecosystem C balance. The objectives of this study were to monitor NEE in high temporal resolution in cropland and grassland between middle August and middle November (2006) at Kleinhohenheim, Germany and to evaluate NEE in autumn. A fully automated temperature controlled closed chamber system with an infrared CO₂ analyzer was used to measure NEE. The measured NEE varied between the two ecosystems depending on changes in above-ground vegetation and environmental factors. The diurnal NEE pattern of daytime CO₂ uptake and night time CO₂ release was evident in the grassland, but not in the cropland as the crops were harvested at the beginning of the measurement period. The grassland generally showed higher night time NEE, but lower daytime NEE than the cropland. Night time NEE showed exponential dependence on air and soil temperature, resulting in Q₁₀ of 1.8 and 1.9 (for air temperature), 2.3 and 2.4 (for soil temperature) in the grassland and cropland, respectively. The average daily NEE was 2.77 and 1.86 g CO₂-C m^?2 day^?1 in the cropland and grassland, respectively. Both ecosystems were sources of CO₂, during 3 months in autumn, but the grassland emitted less CO₂ by 87.9 g CO₂-C m^?2 than the cropland.     

The distribution of phosphorus fractions and desorption characteristics of some soils in the moist savanna zone of West Africa

The fractionation of soil P into various organic and inorganic pools with differing levels of bioavailability, coupled with knowledge of the P adsorption and desorption characteristics of the soils, provides insights into management strategies that enhance P availability to crops. Sequential soil P fractionation was conducted on samples from 11 soil profiles and different experimental fields selected from the derived savanna (DS) and northern Guinea savanna (NGS) zones of the West African moist savanna to assess the influence of soil characteristics and management on soil P pools. Phosphorus adsorption and desorption studies were conducted on samples from the surface horizon of the soil profiles. The total P content varied within and among the soil profiles and tended generally to decrease as depth increased. The total P content in topsoil varied from 90 to 198 mg kg^–1 of which about 30% was organically bound P. The resin P fraction was generally low (mean = 5 mg kg^–1, topsoil) and decreased with depth. These low resin P levels indicate low P availability. Within the DS, where the organic resource (OM) was Senna siamea residues, the effects on soil P fractions of OM and soluble P fertilizer (PF), whether sole or in combination, were site-specific. While resin P was significantly increased by OM in some sites, no significant differences were observed in others. In the NGS fields, farmyard manure (organic resource, OM) combined with PF and PF applied alone increased the inorganic P (Pi) fractions extractable with resin, bicarbonate, and NaOH by about 400% but had no significant effect on the organic P (Po) pools and the more stable Pi forms. The P sorption capacities were low, with the adsorption maximum deduced from the Langmuir equation ranging from 36 to 230 mg kg^–1. The amount of P sorbed to maintain 0.2 mg l^–1 in solution ranged between 0.6 and 16 mg kg^–1. Phosphorus desorption with anion exchange resin differed among the soils, with the recovery of added P ranging from 17 to 66% after 96 h. On average, more of the applied P was recovered in the DS soils than in the NGS soils. Because of the relatively low sorption capacity and the relatively high percentage recovery, small additions of P to most of the soils studied might be adequate for crop growth. In essence, quantities of P fertilizer needed in these soils might be estimated based on considerations of P uptake by crops rather than on sorption characteristics.     

Fluxes of nitrous oxide from soil under different crop rotations and tillage systems in the South of Brazil

The zero tillage (ZT) system is used in a large area (>24 Mha) of crop production in Brazil. This management system can contribute to soil C sequestration, but many studies in other countries have registered greater nitrous oxide emissions under ZT compared to conventional tillage (CT), which may reduce greenhouse gas mitigation benefits. The aim of this study was to estimate the emission of N₂O from cropping systems under conventional and zero tillage in an 18-year-old experiment conducted on a Rhodic Ferralsol in the South of Brazil. Fluxes of N₂O were measured over two years using static-closed chambers in the two tillage systems with three crop rotations. Soil water filled pore space (%WFPS) and soil mineral N were monitored along with rainfall and air temperature. Estimates of N₂O emissions were obtained by integrating the fluxes with time and also by applying the IPCC direct emission factor (EF1 = 1%) to the amounts of N added as fertilisers and returned as crop residues. Fluxes of N₂O were relatively low, apart from a short period at the beginning of measurements. No relationship between N₂O fluxes and %WFPS or mineral N were observed. Nitrous oxide emissions were not influenced either by tillage system or crop rotation. For the crop rotation receiving high rates of N fertiliser in the second year, field-measured N₂O emissions were significantly underestimated by the IPCC emission factor 1 (EF1). For the other treatments measured N₂O emissions fell within the EF1 uncertainty range, but always considerably lower than the EF1 estimate, which suggests IPCC EF1 overestimates true N₂O emissions for the Ferralsol under evaluation.     

Factors influencing the utilization of cattle and chicken manure for soil fertility management by emergent farmers in the moist Midlands of KwaZulu-Natal Province, South Africa

The study established the factors that influence the use of cattle andchicken manure for managing soil fertility by surveying a random sample of 224farm households in the Midlands of KwaZulu-Natal province, South Africa. Themajority (87%) of the respondents are farming on communal land with an averagefarm size of 2.9 ha. Sixty-three% of the farmers in the sampleusedmanure to manage soil fertility in their fields. Despite the fact that chickenmanure was available in large quanties in the area, 54% of manure usedwas from cattle while chicken manure was used by 39% of the sample.Manure was readily available to 73% of the respondent farmers and it wasobtained mostly from commercial and semi-commercial livestock production unitswithin the area. Most of the manure was applied on land planted to high valuecrops such as maize, potatoes and vegetables. The common method of applyingmanure was by a spreader. The major factors that positively influencedthe farmers' decision to use manure were availability of manure, herd size,farmers' experience in farming and the availability of extension services.Both land ownership and attendance of training did not seem to affect thefarmers' decision to use manure. Farm size was the factor that was foundtonegatively affect manure utilization. Other important considerations includedlabor and transport requirements for handling manure, lack of technicalinformation on the fertilizer value and management of manure, increased growthof weeds and bad smell. Some suggestions are made on strategies that couldimprove the efficiency of utilization of manure for soil fertility managementinthis agroecosystem.     

Decomposition,nitrogen and phosphorus mineralization from winter-grown cover crop residues and suitability for a smallholder farming system in South Africa

Increasing land degradation has prompted interest in conservation agriculture which includes growing cover crops. Besides providing soil cover, decaying cover crops may release substantial amounts of nutrients. Decomposition, N and P release from winter cover crops [grazing vetch (Vicia darsycarpa), forage peas (Pisum sativum) and oats (Avena sativa)] were assessed for suitability in a cropping system found in the smallholder irrigation sector of South Africa. Nitrogen and P contribution to maize growth by cover crop residues was also estimated. Decrease in mass of cover crop residues was highest in grazing vetch (7% remaining mass after 124 days) followed by forage peas (16%) and lastly oats (40%). Maximum net mineralized N and P were higher for grazing vetch (84.8 mg N/kg; 3.6 mg P/kg) than for forage peas (66.3 mg N/kg; 2.7 mg P/ha) and oats (13.7 mg N/kg; 2.8 mg P/kg). Grazing vetch and forage pea residues resulted in higher N contribution to maize stover than oat residues. Farmers may use grazing vetch for improvement of soil mineral N while oats may result in enhancement of soil organic matter and reduction land degradation because of their slow decomposition. Terminating legume cover crops a month before planting summer crops synchronizes nutrient release from winter-grown legume cover crops and uptake by summer crops.     

加拿大、南非鞋类产品进出口市场

加拿大据加拿大官方统计,2004年,加拿大进口鞋类产品12.2亿美元,与2003年相比增长了10.77%,近年市场呈平稳增长的趋势。主要的产品供应国包括中国、意大利、越南和巴西。2004年,加拿大从上述四国进口鞋类产品的金额分别为7.01亿美元、9769.9万美元、7538.7万美元和7377.6万美元,分别占当年加拿大鞋类产品进口总额的57.44%、8%、6.18%和6.04%。从中国的进口额比2003年增长了14.33%。另外,2004年加拿大鞋类产品的出口额为1.6亿美元,其主要出口市场是美国。就数量而言,2004年,加拿大进口成品鞋1.28亿双,比2003年增长了7.7%,其中皮面鞋、塑胶非…     

Nitrogen and carbon transformations,water use efficiency and ecosystem productivity in monocultures and wheat-bean intercropping systems

Nutrient Cycling in Agroecosystems - Enhancing soil organic carbon (SOC), nitrogen (N) and water use efficiency (WUE) are significant challenges in intensive wheat production. An intercropping...     

Utilization and management practices of animal manure for replenishing soil fertility among smallscale crop farmers in semi-arid farming districts of the North West Province,South Africa

Poor soil fertility is one of the most limiting biophysical factors to agricultural production among smallscale farmers in much of the sub-Saharan Africa, especially the semi-arid areas. In this study, a survey of 200 randomly selected farming households across four districts (Mafikeng, Ditsobotla, Ganyesa and Taung) located in a semi-arid environment of the North West Province in South Africa was conducted to establish the utilisation and management of animal manure for managing soil fertility. The results showed that 66% of the farmers across the districts used animal manure on their crops. The types of manure used were in the order cattle > sheep = goat > chicken. Cattle manure was readily available from farmers’ own kraal or neighbours. Despite its availability and advantages, chicken manure was seldom used. The rates of manure application were generally low (mean 2.5 tha⁻¹) although most farmers (71%) applied it annually. In the majority of cases, manure would be applied to about half (57.5%) of the cropped land every year (average farm size was 5.3 hectares). The manure was mostly broadcasted (76%) on the surface before being ploughed under followed by dollop (53%). The quality of most of the manure resources was relatively poor as it had low N and P but high soil content (mean 22.7%). The study found that farmers have developed local knowledge with regards to criteria for defining manure quality. The criterion, which used physical characteristics such as colour, moisture content and presence of moulds in the manure, was quite consistent across the study districts and points to the possibility of the indigenous knowledge being interfaced with scientific knowledge. The factors which positively influenced farmers’ decision to use manure were herd sizes, farming experience, training and availability of manure, extension services and labour. On the other hand, farm sizes negatively affected manure use. It was observed that housing, feeding, storage and handling practices of manure resources was not optimum in most of the study districts and this contributed to loss of nutrients and quality. It is recommended that improved strategies of manure production and handling be adopted by farmers in order to maximise the quality and efficiency of manure utilization. The potential that exists in using chicken manure to supply crop nutrients needs to be explored.     

Farm typologies,soil fertility variability and nutrient management in smallholder farming in Sub-Saharan Africa

Farm typologies are a useful tool to assist in unpacking and understanding the wide diversity among smallholder farms to improve targeting of crop production intensification strategies. Sustainable crop production intensification will require the development of an array of nutrient management strategies tailored to farm-specific conditions, rather than blanket recommendations across diverse farms. This study reviewed key literature on smallholder farm typologies focusing on three countries (Kenya, Malawi and Zimbabwe), to gain insights on opportunities for crop production intensification, and the importance of developing farm-specific nutrient management practices. Investigations on farm typologies have done well in highlighting the fundamental differences between farm categories, with 3–5 typologies often adequate to represent the wide differences in resource endowment. Resource-endowed farmers have ready access to large quantities of manure and mineral fertilizers, which contribute to higher soil fertility and crop productivity on their farms. Resource-constrained households use little or no manure and mineral fertilizers, and have limited capacity to invest in labour-demanding soil fertility management technologies. These farmers often have to rely on off-farm opportunities for income that are largely limited to selling unskilled labour to their resource-endowed neighbors. The variability in management practices by farmers has resulted in three main soil fertility classes that can be used for targeting soil fertility management technologies, characterized by potential response to fertilizer application as: (1) low-responsive fertile fields that receive large additions of manure and fertilizer; (2) high-responsive infertile fields that receive moderate nutrient applications; (3) poorly responsive degraded soils cultivated for many years with little or no nutrient additions. The main conclusions drawn from the review are: (1) resource constrained farmers constitute the widest band across the three countries, with many of the farmers far below the threshold for sustainable maize production intensification and lacking capacity to invest in improved seed and fertilizer, (2) farm sizes and livestock ownership were key determinants for both farmer wealth status and farm productivity, and (3) soil organic carbon and available P were good indicators for predicting previous land management, that is also invariably linked to farmer resource endowment.     

Soil nitrous oxide emissions under different management practices in the semiarid region of the Argentinian Pampas

The aim of this study was to analyze the influence of different crop sequences (soybean-corn and soybean?Csoybean) and tillage systems (no tillage and reduced tillage) on nitrous oxide (N₂O) soil emissions under field conditions. The experiment was carried out in Manfredi, Córdoba province, Argentina on an Entic Haplustoll and N₂O emissions were measured in the field during a year. N₂O fluxes were low during winter, but in late spring it peaked. For fallow, N-NO₃-content was the most important variable to explain N₂O emissions. For growing period water-filled pores was the main variable explaining N₂O emissions. Nitrogen fertilization of corn crop increased N₂O-N emissions, whereas no significant differences were found due to the tillage system. Measured annual N₂O-N emissions were generally lower than those calculated using the methodology proposed by the Intergovernmental Panel on Climate Change.     

Nitrogen and phosphorus capture and recovery efficiencies,and crop responses to a range of soil fertility management strategies in sub-Saharan Africa

This paper examines a number of agronomic field experiments in different regions of sub-Saharan Africa to assess the associated variability in the efficiencies with which applied and available nutrients are taken up by crops under a wide range of management and environmental conditions. We consider N and P capture efficiencies (NCE and PCE, kg uptake kg⁻¹ nutrient availability), and N and P recovery efficiencies (NRE and PRE, kg uptake kg⁻¹ nutrient added). The analyzed cropping systems employed different soil fertility management practices that included (1) N and P mineral fertilizers (as sole or their combinations) (2) cattle manure composted then applied or applied directly to fields through animal corralling, and legume based systems separated into (3) improved fallows/cover crops-cereal sequences, and (4) grain legume-cereal rotations. Crop responses to added nutrients varied widely, which is a logical consequence of the wide diversity in the balance of production resources across regions from arid through wet tropics, coupled with an equally large array of management practices and inter-season variability. The NCE ranged from 0.05 to 0.98 kg kg⁻¹ for the different systems (NP fertilizers, 0.16–0.98; fallow/cover crops, 0.05–0.75; animal manure, 0.10–0.74 kg kg⁻¹), while PCE ranged from 0.09 to 0.71 kg kg⁻¹, depending on soil conditions. The respective NREs averaged 0.38, 0.23 and 0.25 kg kg⁻¹. Cases were found where NREs were >1 for mineral fertilizers or negative when poor quality manure immobilized soil N, while response to P was in many cases poor due to P fixation by soils. Other than good agronomy, it was apparent that flexible systems of fertilization that vary N input according to the current seasonal rainfall pattern offer opportunities for high resource capture and recovery efficiencies in semi-arid areas. We suggest the use of cropping systems modeling approaches to hasten the understanding of Africa’s complex cropping systems.