The prospects for integrated nutrient management for sustainable rainfed lowland rice production in Sukumaland, Tanzania

The possibilities of integrated nutrient management for sustainable ricecultivation are investigated for rainfed, lowland rice in Sukumaland,northwestern Tanzania. Typical, hardpan rice soils in Sukumaland have ratherlowlevels of organic matter, total nitrogen and available phosphorus, and a low tomedium amount of exchangeable potassium. Consumption of mineral fertilizers inrice is, however, very low due to availability problems and sharply increasedprices of fertilizers. Use of locally available resources for soil fertilityimprovement is hampered by the additional inputs of farm household labourinvolved. High labour inputs per hectare without increases in capital inputslead to lower marginal and average products per hour of labour. Furthermore, insemi-arid Sukumaland biomass production of green manures is seriouslyrestrictedby climate. The amount of kraal cattle manure is insufficient and half thehouseholds have no easy access to it. Using rice straw as cattle feed andthatching material has priority over soil fertility improvement. Some farmersindicate that at present there is not yet an urgent need for improvedintegratednutrient management in Sukumaland rice cultivation. Adoption of integratednutrient management based technologies depends on conducive socio-economic,agro-ecological and public policy circumstances. Farmer investment in learningand a favourable policy environment are thus no guarantee for worldwideadoptionof these technologies by farm households.     

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.     

Economic benefits of combining soil and water conservation measures with nutrient management in semiarid Burkina Faso

Nutrient limitation is the main cause of per capita decline in crop production in the Sahel, where water shortage also limits an efficient use of available nutrients. Combining soil and water conservation measures with locally available nutrient inputs may optimize crop production and economic benefit in cereal-based farming systems. A study conducted in 2001 and 2002 at Saria, Burkina Faso (annual rainfall 800 mm, PET of 2000 mm yr^–1) assessed the combined effects of two types of semi-permeable barriers (stone rows and grass strips of Andropogon gayanus Kunth cv. Bisquamulatus (Hochst.) Hack.) and the application of compost or urea on sorghum performance and economic benefits. The field experiment was carried out on a Ferric Lixisol, 1.5% slope and comprised 9 treatments in which the barriers were put along contours and combined with compost-N or urea-N. Installation of stone rows or grass strips without addition of nutrient inputs was not cost effective, although it induced sorghum yield increase (12–58%) particularly under poor rainfall conditions. Combining compost with stone rows or grass strips significantly increased sorghum yield that induced positive interaction effects (mean added effects of 185 kg ha^–1 for stone rows combined with compost-N and 300 kg ha^–1 for grass strips combined with compost-N). Economic benefits were substantial (109 480 to 138 180 FCFA ha^–1) when compost-N was added to both stone rows and grass strips, whereas limited economic benefits were observed with the application of urea-N (1120 to 22 120 FCFA ha^–1). This may provide farmers with capital to invest in soil management and may also contribute to poverty alleviation in sub-Saharan Africa.     

Economic benefits of combining soil and water conservation measures with nutrient management in semiarid Burkina Faso

Nutrient limitation is the main cause of per capita decline in crop production in the Sahel, where water shortage also limits an efficient use of available nutrients. Combining soil and water conservation measures with locally available nutrient inputs may optimize crop production and economic benefit in cereal-based farming systems. A study conducted in 2001 and 2002 at Saria, Burkina Faso (annual rainfall 800 mm, PET of 2000 mm yr^–1) assessed the combined effects of two types of semi-permeable barriers (stone rows and grass strips of Andropogon gayanus Kunth cv. Bisquamulatus (Hochst.) Hack.) and the application of compost or urea on sorghum performance and economic benefits. The field experiment was carried out on a Ferric Lixisol, 1.5% slope and comprised 9 treatments in which the barriers were put along contours and combined with compost-N or urea-N. Installation of stone rows or grass strips without addition of nutrient inputs was not cost effective, although it induced sorghum yield increase (12–58%) particularly under poor rainfall conditions. Combining compost with stone rows or grass strips significantly increased sorghum yield that induced positive interaction effects (mean added effects of 185 kg ha^–1 for stone rows combined with compost-N and 300 kg ha^–1 for grass strips combined with compost-N). Economic benefits were substantial (109 480 to 138 180 FCFA ha^–1) when compost-N was added to both stone rows and grass strips, whereas limited economic benefits were observed with the application of urea-N (1120 to 22 120 FCFA ha^–1). This may provide farmers with capital to invest in soil management and may also contribute to poverty alleviation in sub-Saharan Africa.     

Processes controlling soil phosphorus release to runoff and implications for agricultural management

Phosphorus (P) loss from agricultural land to surface waters is well known as an environmental issue because of the role of P in freshwater eutrophication. Much research has been conducted on the erosion and loss of P in sediments and surface runoff. Recently, P loss in sub-surface runoff via agricultural drainage has been identified as environmentally significant. High soil P levels are considered as a potential source of P loss. However, without favourable hydrological conditions P will not move. In this paper, we review the basis of soil P release into solution and transport in surface and sub-surface runoff. Our objectives are to outline the role of soil P and hydrology in P movement and management practices that can minimize P loss to surface waters. Remedial strategies to reduce the risk of P loss in the short-term are discussed, although it is acknowledged that long-term solutions must focus on achieving a balance between P inputs in fertilizers and feed and P outputs in production systems. This revised version was published online in June 2006 with corrections to the Cover Date.     

Organic residue management,soil nutrient changes and maize yield in a humid Ultisol

A study was conducted on an Oxic Paleudult in South Western Nigeria to evaluate the effects of organic residue treatments after clearing a 3 year secondary fallow land on soil nutrients, maize yield and profitability. Burning of the fallow residue in 1993 and crop residue in situ in 1994 led to significant increases in soil pH, total N, organic matter, available P, exchangeable Ca, Mg and K within one month in both fertilized and unfertilized treatments. However, the increases were not sustained till harvest and in most cases the concentrations of the nutrients decreased significantly below the pretreatment levels. Increases due to residue incorporation were small but more sustainable, while in bare unfertilized plots the nutrients decreased below the pre treatment levels throughout the period of the experiment. Maize yields were significantly higher in residue incorporated and burnt plots than in the bare plots with or without fertilizer application in both years. The influence of fertilizer application was profound. However, residue incorporation without fertilizer produced 84% of the yield obtained in bare fertilized plots in 1993 and as much as 104% in 1994. The highest profit was obtained when fertilizer application was combined with residue incorporation.     

Fate of phosphorus applied in slurry and mineral fertilizer: accumulation in soil and release into surface runoff water

Phosphorus (P) accumulation on the soil surface and its effect on the concentration of dissolved orthophosphate P (PO₄-P) in surface runoff water were studied after three years of surface application of slurry and mineral fertilizer to grass ley on a sandy soil, poor in P. The total amount of P applied was 107–143 kg ha^–1>, of which 72–119 kg ha^–1> was applied on the soil surface during two or three years without incorporation or mixing. The addition of slurry and mineral fertilizer resulted in an increase in inorganic P in the 0–5 cm but not the 5–25 cm soil layer, but organic P was not affected. The measured changes in inorganic P deviated only by 4–6 kg ha^–1> from the values derived from inputs and outputs of P (crop uptake + losses in surface runoff and drainage water). The increase in inorganic-P was accompanied by increases in the degree of P saturation (DPS) and in P extracted with acid am monium acetate (P_Ac ), sodium bicarbonate (P_Olsen) and anion-exchange resin (P_Resin). In surface runoff, 10–18 months after the last surface application of P, the mean flow-weighted concentration of PO₄-P was linearly increased with the values of DPS, P_Ac, P_Olson and P_Resin in the 0–5 cm soil layer. PO₄-P was lowest (0.033 mg l^–1> ) in the control plots and highest (0.62 mg l^–1>) in the plot where 143 kg ha^–1> P had been applied in slurry and fertilizer. On that plot, the corresponding values of DPS, P_Ac, P_Olson and P_Resin were 16%, 13 mg kg^–1>, 85 mg kg^–1> and 71 mg kg^–1 , even within a few years, and multiply the P loading to surface runoff from the site. A very shallow soil sampling (< 5 cm) is needed to assess P loading potential in a soil where P has been surface-applied.     

Effect of farmer management strategies on spatial variability of soil fertility and crop nutrient uptake in contrasting agro-ecological zones in Zimbabwe

Variability of soil fertility within, and across farms, poses a major challenge for increasing crop productivity in smallholder systems of sub-Saharan Africa. This study assessed the effect of farmers’ resource endowment and nutrient management strategies on variability in soil fertility and plant nutrient uptake between different fields in Gokwe South (ave. rainfall ~650 mm year⁻¹; 16.3 persons km⁻²) and Murewa (ave. rainfall ~850 mm year⁻¹; 44.1 persons km⁻²) districts, Zimbabwe. In Murewa, resource-endowed farmers applied manure (>3.5 t ha⁻¹ year⁻¹) on fields closest to their homesteads (homefields) and none to fields further away (outfields). In Gokwe the manure was not targeted to any particular field, and farmers quickly abandoned outfields and opened up new fields further way from the homestead once fertility had declined, but homefields were continually cultivated. Soil available P was higher in homefields (8–13 mg kg⁻¹) of resource-endowed farmers than on outfields and all fields on resource constrained farms (2–6 mg kg⁻¹) in Murewa. Soil fertility decreased with increasing distance from the homestead in Murewa while the reverse trend occurred in Gokwe South, indicating the impact of different soil fertility management strategies on spatial soil fertility gradients. In both districts, maize showed deficiency of N and P, implying that these were the most limiting nutrients. It was concluded that besides farmers’ access to resources, the direction of soil fertility gradients also depends on agro-ecological conditions which influence resource management strategies.     

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.     

Multiobjective optimization for designing and operating more sustainable water management systems for a city in Mexico

This article proposes a multiobjective optimization model for the design of a macroscopic water system of a Mexican city that solves simultaneously the planning and scheduling of water storage and distribution tasks. The model, which considers rainwater harvesting and reclaimed water reusing as alternative water sources, maximizes the revenues from water sales and minimizes simultaneously the water consumption and land use. A case study based on the city of Morelia in Mexico was solved. It was found that the use of alternative water sources (such as harvested rainwater) along with an appropriate planning and scheduling of storage and distribution tasks have the potential to reduce the pressure over natural reservoirs significantly. Our approach considers simultaneously economic and environmental concerns, thereby contributing to the implementation of more sustainable alternatives in urban water distribution. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2428–2446, 2015     

Effect of fertilizer type,sampling depth,and years on Colwell soil test phosphorus for phosphorus leaching soils

The relationships between (i) soil test phosphorus (P) (Colwell sodium bicarbonate procedure) and the level of P applied (from 0 to 1000 kg total P ha^–1) (relationship 1), and (ii) yield and soil-test P (relationship 2, the soil P test calibration), were measured in two field experiments on very sandy, P-leaching soils in the high rainfall (> 800 mm annual average) areas of south-western Australia. The soils were humic sandy podzols, or haplohumods, comprising 97% sand (20 to 2000 m). The experiments started in April 1984 and were terminated at the end of 1990. Soil-test P, measured on soil samples collected to 5, 10 and 25 cm depth each January in the years after P application, was related to yields of dried clover (Trifolium subterraneum) herbage measured later in each year. The four P fertilizers studied were single superphosphate, coastal superphosphate (made by adding, just before granulation, extra rock phosphate together with elemental sulphur while manufacturing single superphosphate), apatite rock phosphate, and Calciphos.Relationship (1) was adequately described by a linear equation (R² > 0.80, most being > 0.90). The slope coefficient estimates the extractability of P from the soil by the Colwell procedure, and is called extractability. Relationship (2) was adequately described by the Mitscherlich equation (R² > 0.75, most being > 0.90). For relationship (2), use of percentage of the maximum (relative) yield eliminated differences due to different maximum yields and yield responses (maximum yield minus the yield for the nil-P treatment). Soil test P ranged from about 4 to 150 g Pg^–1 soil. Soil test P and extractability were generally higher for samples of the top 5 cm of the soil than the top 25 cm, and were largest for single superphosphate and lowest for apatite rock phosphate. Both extractability (relationship (1)) and the curvature coefficient of the Mitscherlich equation (relationship (2)), differed for different P fertilizers and different soil sample depths. The curvature coefficient also differed for different yield assessments (harvests) in the same or different years. Different soil P test calibrations were required for different P fertilizers, soil sample depths and harvest in the same or different years. It is concluded that soil P testing provides a crude estimate of the current P status of P-leaching soils in Western Australia.     

Modeling of soil nutrient balances,flows and stocks revealed effects of management on soil fertility in south Ecuadorian smallholder farming systems

Nutrient Cycling in Agroecosystems - Linking nutrient balances and flows to soil nutrient stocks creates a valuable indicator for sustainability assessment in agricultural land-use systems....     

Nitrogen fertilizer use in China – Contributions to food production, impacts on the environment and best management strategies

China is a big country with a huge population and limited farmland area per capita. To produce enough food for feeding the population is of vital importance for the county. A huge achievement in food production since 1949 has been made. The regression analysis in each period of 10 years shows that there is a significant positive linear correlation between the annual food production and annual chemical fertilizer N (CF-N) consumption throughout 1949–1998. However, the regression coefficient, b, in each period of 10 years since 1949 has been declining rapidly. Meanwhile, environmental pollution is becoming a serious issue. In last 20 years, N concentratjons in surface and ground water have been increasing, `Alga blooms' in lakes and `red tides' in estuaries occur frequently, and the emissions of N₂O and NH₃ from farmlands rise. This paper reviews the causes for the declining N efficiency and rising environmental impacts, and the strategies for better fertilizer management.     

Membrane processes for water,pulp and paper,food state of the art

General trends, observations and personal viewpoints are presented on membrane processes for the water, pulp and paper, and the food industry. Thus electrodialysis, reverse osmosis and ultrafiltration are considered form their historic and economic aspects, and thoughts are advanced on how and why institutions and companies have entered this technology and which entities will be leading the development in the eighties.     

Ternary doping of phosphorus,nitrogen, and sulfur into porous carbon for enhancing electrocatalytic oxygen reduction

We report a synthesis of phosphorus (P), nitrogen (N) and sulfur (S) ternary co-doped porous carbon (PNS-PC) which acts as efficient metal-free electrocatalyst for the ORR. PNS-PC has been fabricated via an electrostatic assembly method followed by a carbonization process. Tetraphenylphosphonium bromide is employed as carbon and phosphorus source and ammonium persulfate as nitrogen and sulfur source. The as-prepared PNS-PC possesses high BET specific surface area (>580 m² g⁻¹). The most active PNS-PC that containing 1.44 at.% P, 2.96 at.% N and 2.65 at.% S exhibits much enhanced electrocatalytic activity for the ORR compared to solely P-doped carbon (P-C) in alkaline media. This PNS-PC shows an onset potential of 0.905 V (vs. RHE), which is 120 mV higher than that of P-C. A negative shift of only about 68 mV in the half-wave potential of the PNS-PC as compared to commercial Pt/C (20 wt.% Pt on Vulcan XC-72, Johnson Matthey) is achieved. The high electrocatalytic activity of the PNS-PC is primarily attributed to the synergistic effect of P, N and S ternary doping in carbon and its hierarchical porous structure. The results demonstrate that multiple element doping is an efficient way for enhancing the electrocatalytic activity of carbon for ORR.