Soil is a fundamental requirement for crop production as it provides plants with anchorage, water and nutrients. A certain supply of mineral and organic nutrient sources is present in soils, but these often have to be supplemented with external applications, or fertilisers, for better plant growth. Fertilisers enhance soil fertility and are applied to promote plant growth, improve crop yields and support agricultural intensification.
Fertilisers are typically classified as organic or mineral. Organic fertilisers are derived from substances of plant or animal origin, such as manure, compost, seaweed and cereal straw. Organic fertilisers generally contain lower levels of plant nutrients as they are combined with organic matter that improves the soils physical and biological characteristics. The most widely-used mineral fertilisers are based on nitrogen, potassium and phosphate.
Optimal and balanced use of nutrient inputs from mineral fertilisers will be of fundamental importance to meet growing global demand for food (International Food Policy Research Institute, 1995). Mineral fertiliser use has increased almost fivefold since 1960 and has significantly supported global population growth — Smil (2002) estimates that nitrogen-based fertiliser has contributed an estimated 40 per cent to the increases in per-capita food production in the past 50 years. Nevertheless, environmental concerns and economic constraints mean that crop nutrient requirements should not be met solely through mineral fertilisers. Efficient use of all nutrient sources, including organic sources, recyclable wastes, mineral fertilisers and biofertilisers should therefore be promoted through Integrated Nutrient Management (Roy et al, 2006).
The aim of Integrated Nutrient Management (INM) is to integrate the use of natural and man-made soil nutrients to increase crop productivity and preserve soil productivity for future generations (FAO, 1995a). Rather than focusing nutrition management practices on one crop, INM aims at optimal use of nutrient sources on a cropping-system or crop-rotation basis. This encourages farmers to focus on long-term planning and make greater consideration for environmental impacts.
INM relies on a number of factors, including appropriate nutrient application and conservation and the transfer of knowledge about INM practices to farmers and researchers. Boosting plant nutrients can be achieved by a range of practices covered in this guide such as terracing, alley cropping, conservation tillage, intercropping, and crop rotation. Given that these technologies are covered elsewhere in this guidebook, this section will focus on INM as it relates to appropriate fertiliser use. In addition to the standard selection and application of fertilisers, INM practices include new techniques such as deep placement of fertilisers and the use of inhibitors or urea coatings (use of area coating agent helps to retart the activity and growth of the bacteria responsible for denitrification) that have been developed to improve nutrient uptake.
Key components of the INM approach include:
1) Testing procedures to determine nutrient availability and deficiencies in plants and soils. These are:
- Plant symptom analysis – visual clues can provide indications of specific nutrient deficiencies. For example, nitrogen deficient plants appear stunted and pale compared to healthy plants
- Tissue analysis and soil testing – where symptoms are not visible, post-harvest tissue and soil samples can be analysed in a laboratory and compared with a reference sample from a healthy plant
2) Systematic appraisal of constraints and opportunities in the current soil fertility management practices and how these relate to the nutrient diagnosis, for example insufficient or excessive use of fertilisers.
3) Assessment of productivity and sustainability of farming systems. Different climates, soil types, crops, farming practices, and technologies dictate the correct balance of nutrients necessary. Once these factors are understood, appropriate INM technologies can be selected
4) Participatory farmer-led INM technology experimentation and development. The need for locally appropriate technologies means that farmer involvement in the testing and analysis of any INM technology is essential (Box 1).
Box 1: On-farm Testing of Integrated Nutrient Management Strategies in Eastern Uganda
“An action research project carried out by CIAT (Centro Internacional de Agricultura Tropical) in three villages in Eastern Uganda implemented participatory on-farm testing of farmer-designed INM strategies during a two-year process. Twenty farmers representing three soil fertility management classes in the three villages were chosen by the farmer groups as test farmers for intensive monitoring of the on-farm experimentation.
During the diagnostic phase of the PLAR process farmers analysed soil fertility management diversity and resource endowment resulting in the identification and prioritisation of 12 soil fertility and management constraints. Drought was the main constraint, followed by lack of knowledge and skills on soil fertility management, low inherent soil fertility, and soil-borne diseases and pests. The high cost of inorganic fertilisers was ranked number sixth, while soil erosion and poor tillage methods were ranked seventh. During the planning phase, farmers were taken on a farmer exchange visit to meet other farmer innovators who practise some of the proposed technologies.
Farmers designed 11 experiments and they proposed data collection procedures for monitoring and evaluation. Soil samples were collected for laboratory analysis and plant growth was monitored for germination percentage, crop performance, weed management, pests and disease incidence, time of harvesting, and crop yield
Application of farmyard manure at 10 t/ha fresh weight tended to improve maize grain yield in the two years of the project. Although the grain yield increases were not significant, farmers were ready to adapt the technology at large-scale. However, the availability, quantity and quality of the manure in the area is a major constraint to wide-scale adoption of this technology. The farmers designed an experiment to evaluate various sources of phosphorous fertilisers. There were five treatments or different mixes, including a control with no fertilisers. There was significant response to the various sources of phosphate fertilisers on maize grain yield. However, capital constraints were identified as limiting factors affecting further adoption of this technology. Green manure application did not significantly improve maize yields however the mean annual dry matter (biomass) yields were significantly different. Farmers in the test area have been using green manure for more than five years. Therefore it was proposed that this technology be disseminated without any further on-farm testing.
Farmer evaluation of on-farm experiments shows that simple, inexpensive technologies requiring little labour and locally available resources have a high potential for adoption. However, bio-economic modelling studies showed that a substantial improvement in the socio-economic environment is needed to give farmers sufficient incentives to adopt more sustainable land management practices. The results support the hypothesis that systematic learning with stakeholders, and farmers perceiving economic incentives, are necessary for changing farming practices. However, the capacity of different farmers to invest in improving soil fertility management depends on access to labour, livestock, land, capital and cash at the household level. The options available to poor farmers are much more constrained than those available to the well endowed farmers who are able to invest in large-scale use of organic and inorganic sources of nutrients.”
Source: Esilaba et al, 2004
Harsh climatic conditions are a major cause of soil erosion and the depletion of nutrient stocks. By increasing soil fertility and improving plant health, INM can have positive effects on crops in the following ways:
- A good supply of phosphorous, nitrogen and potassium has been shown to exert a considerable influence on the susceptibility or resistance of plants towards many types of pests and diseases
- A crop receiving balanced nutrition is able to explore a larger volume of soil in order to access water and nutrients. In addition, improved root development enables the plant to access water from deeper soil layers. With a well-developed root system, crops are less susceptible to drought
- Under increasingly saline conditions, plants can be supplemented with potassium to maintain normal growth
- With appropriate potassium fertilisation, the freezing point of the cell sap is lowered, thus improving tolerance to colder conditions (Figure 1)
INM enables the adaptation of plant nutrition and soil fertility management in farming systems to site characteristics, taking advantage of the combined and harmonious use of organic and inorganic nutrient resources to serve the concurrent needs of food production and economic, environmental and social viability. INM empowers farmers by increasing their technical expertise and decision-making capacity. It also promotes changes in land use, crop rotations, and interactions between forestry, livestock and cropping systems as part of agricultural intensification and diversification.
As well as facilitating adaptation to climate change in the agriculture sector, the INM approach is also sensitive to changes in climatic conditions and could produce negative effects if soil and crop nutrients are not monitored systematically and changes to fertiliser practices made accordingly. In Africa, high transport costs in land-locked countries contribute to prohibitively high fertiliser prices (FAO, 2008b). In the case of small-scale farmers these costs may represent too high a proportion of the total variable cost of production thus ruling out inorganic fertiliser as a feasible option.
The main cost associated with Integrated Nutrient Management relates to the purchase and distribution of inorganic fertilisers which are affected by a range of factors (Table 1).
Table 1: Average cost of fertilizers per metric ton in Africa
|Country||Factors affecting cost||Cost|
Private market dominated by a single importer making low-volume purchases
Absence of retail network resulting in low provision to rural areas
Very high transportation costs and poor road infrastructure
No local manufacturing or blending facilitiesLow fertiliser demand and consumption
Land locked country
Fertilisers make up one of the four largest markets in the country. Net importer with some local production.
Government plays central role in importation and delivery through public tender
Choice of port (South Africa, Tanzania or Mozambique) greatly affects cost and availability
High transport costs due to high fuel prices and poor road infrastructure
Subsidised fertiliser programme with farmer voucher schemeExcessive importer, wholesale, and retail margins
All fertilisers imported
Privatised market dominated by three major importer- wholesalers
Well-organised distributors and dealers
No direct import duties or sales tax
Market in growth phase
Market price competition robust
Predominantly ship (from international suppliers) and truck transport (from Nigerian suppliers and to distributors)
High storage costs at portsHigh inland transport costs
Source: Chemonics, 2007
Organic fertilisers provide a low-to-no-cost technology for improving soil fertility as long as they can be produced and used within a relatively close distance.
The success of INM will depend upon the combined efforts of farmers, researchers, extension agents, governments, and NGOs. Simply providing fertilisers is not enough to support INM implementation. Appropriate policy frameworks are essential, as are market structures, infrastructure development, credit facilities and the transfer of technology and knowledge.
INM requires knowledge of what is required by plants for optimum level of production ─ in what different forms and at what different timings and how these requirements can be integrated to obtain highest productivity levels within acceptable economic and environmental limits. Determining this information will require localised research but will also benefit from the cooperation of national and international agricultural research centres. Extension staff who are able to translate research data into practical recommendations will need to take account of both farmers’ expertise and applicable research results. Available knowledge will need to be summarised and evaluated economically in order to provide practical guidelines for the adoption of INM by farmers that have a range of investment capacities.
An insufficient availability of credit at an affordable price is frequently mentioned as a constraint on fertiliser use. Access to mineral fertiliser may be limited in rural or underdeveloped areas due to high import prices and high transport costs. A lack of adequate infrastructure for distribution and conservation can also present a barrier for access and use. In addition, fertilisers have a limited shelf-life and may be in high demand (leading to shortages) in peak seasons if appropriate planning is not put in place. Competition for organic resources may be high in areas where crop residues are used for fuel and animal feed.
A largely untapped source of potential fertiliser is urban waste. Although the quality or fertiliser produced from urban waste does not compare to commercially produced fertiliser, the sludge (Residual, semi-solid material left from industrial wastewater, or sewage treatment processes) contains nitrogen, phosphorous, potassium and other micro-nutrients. Utilising urban waste for agricultural lands near urban centres puts to good use a material that otherwise would be disposed via costly means (Gruhn et al, 2000). Farmers associations and extension services provide an opportunity for production and dissemination of information on the most cost-effective and appropriate technologies.
Chemonics (2007) Fertiliser Supply and Costs in Africa, Chemonics Inc.
Esilaba, A. O., J. B. Byalebeka, R. J. Delve, J. R. Okalebo, D. Ssenyange, M. Mbalule and H. Ssali (2004) “On farm testing of integrated nutrient management strategies in eastern Uganda”. Agricultural Systems.
FAO (1995a) Integrated plant nutrition system. FAO Fertiliser and Plant Nutrition Bulletin No. 12. Rome. 426 pp.
FAO (2008b) Current world fertiliser trends and outlook to 2011/12, FAO, Rome
Gruhn, P., F. Goletti, M. Yudelman (2000) Integrated nutrient management, soil fertility and sustainable agriculture: current issues and future challenges, IFRPI 2020 Vision Brief.
IFPRI (International Food Policy Research Institute) (1995) Biophysical limits to global food production (2020 Vision). Washington, DC. 2.
Roy, R. N., A. Finck, G. J. Blair and H. L. S. Tandon (2006) Plant nutrition for food security, FAO Rome, 2006.
Smil, V. (2002) Nitrogen and food production: Proteins for human diets. Ambio, 31: 126–131.