Improving productivity of Nigerian soil

By Ishaku Amapu, Department of Soil Science, Ahmadu Bello University, Zaria

Abba Ruma,
Minister of Agriculture

MOST soils of Nigeria, like other parts of sub-Saharan Africa, are poor compared to most other parts of the world. It has been posited that lack of volcanic rejuvenation has caused the continent to undergo various cycles of weathering (breakdown of rocks into soils), erosion (loss of soil by forces of water or wind) and leaching (washing down of nutrients by water), leaving the soils poor in nutrients. The use-efficiency of most inputs used in crop production is therefore low, albeit the favourable weather conditions, especially of elements such as temperature and radiation. One of the plant nutrients that are in very short supply and the principal cause of the “inherent poor soil fertility” status of most of these soils is phosphorus.

The prominent place of phosphorus: Phosphorus has been called ‘the key to life’.

This is because it is directly involved in most life processes. In terms of frequency of use in agriculture, it is second only to nitrogen as an essential plant nutrient. Phosphorus occurs in plants in organic and inorganic forms. In the organic forms it is linked by pyrophosphate bonds. The most important compound which phosphate groups are linked by pyrophosphate bonds is adenosine triphosphate (ATP).

This is the energy molecule, which supplies all biochemical processes; the energy required for synthesizing molecules and for the uptake and transport of nutrients ions in plants. In addition to other specific roles, the triphosphates, are also involved in the synthesis (manufacture) of ribonucleic acids (RNA) and deoxyribonucleic acids (DNA). DNA is a carrier of genetic information, and various forms of RNA function in protein synthesis in both animals and plants. Another important organic phosphorus compound is phytin. Phosphorus in phytin of seeds is generally regarded as a preserve.

During seed germination phytin P is mobilized and converted into other phosphate forms needed in the metabolism of young plants. When this seed Preserve is exhausted the seedling could die in soils containing very low phosphorus. The above show the universal and essential role of phosphorus not only in plants but in all living organisms. Because of the many and varied functions exerted by phosphorus in plant metabolism inadequate supply to the plant seriously affects numerous metabolic processes. The end result is not only low crop yields but also poor quality fruits and seeds.

In addition to the important roles phosphorus has in crop nutrition, it also plays very significant roles in influencing the efficient utilization of other plant nutrients. This is because nutrients interact in soil and plant. Some of these relationships are antagonistic (negative) while some are synergistic (mutually beneficial). Phosphorus has been found to have synergistic interactions with almost all nutrients considered essential for the nutrition of crop plants. In nearly all of these relationships it is phosphorus that ‘encourages’ the better functioning of the other nutrients.

From the foregoing, it is obvious that when phosphorus is deficient in soil other inputs and technologies may not be effective.

This makes it an indispensable component of any successful crop production venture. It is key to the concept of balanced fertilization which does not only mean a certain definite proportion of nitrogen, phosphorus and potash or other nutrients to be added in the form of fertilizer, but the availability of nutrients already present in the soil, crop requirement and other factors. Balanced fertilization also takes into account the crop removal of nutrients, the economics of fertilizers and profitability, farmer’s ability to invest, agrotechniques, soil moisture regime, weed control, plant protection, seed rate, sowing time, soil salinity, alkalinity, physical environment, microbiological condition of the soil, available nutrient status of soil, cropping sequence, etc. It is not a state but a dynamic concept. Phosphorus is unique because it is not only an essential plant nutrient but also a soil amendment. So its ability to play pivotal roles in balanced fertilization. Unfortunately, unlike nitrogen, there appears to be no great potential for organic or biological P sources of plant nutrition. Due to economic considerations, the cost of applying imported or locally produced water-soluble P fertilizers is often more expensive than utilizing indigenous rock phosphate. The direct application of phosphate rock (PR) therefore becomes the most attractive alternative. In recent years PR for direct application has been tested in tropical acid soils as a potential alternative to conventional water-soluble P fertilizers like single superphosphate (SSP) and triple superphosphate (TSP).

Need to actualize past and on-going proposals
The unique roles of phosphorus taken with the economic considerations of applying imported or locally produced water­soluble P fertilizers must have prompted the World Bank to propose the use of phosphate rock as a capital investment in soils of sub-Saharan Africa. This nutrient was singled out as the one with the greatest potential of increasing the productivity and conserving the resource base of this region. The document (1) is emphatic about the fact that for other technologies (high yielding crop varieties, nitrogen and potassium fertilizers etc) to be efficiently used, phosphorus must first be applied in the low P soils. The World Bank is treating this issue more as an environmental issue than an agricultural one. The document emphasizes that conservation of the resource base is not only a necessity for sub Saharan Africa but also a global concern. Furthermore, the document noted that sub-Saharan Africa had abundant reserves of phosphate minerals and yet P deficiency was a major cause of poverty in the region. Nigeria has its fair share of deposits of the phosphate rock (the raw material used in manufacturing P fertilizers). The World Bank’s proposal to use phosphate as a capital investment was concurred at the Africa Fertilizer Summit held in Abuja , Nigeria in June 2006. The idea of capitalizing the soil with phosphate is not all that new. Many ‘developed’ countries of the world did this many years ago and have reaped tremendous benefits. A number of steps can be identified in the use of fertilizers in European agriculture. First, widespread P deficiency in soils had to be corrected and this was made possible by the industrial scale production of superphosphate in the mid-1800s. Therefore, at present, the phosphorus status of the soils in many European countries is at a satisfactory level. Today, agricultural productivity in many developed countries relies heavily on the input of nutrients from fertilizers. The financial returns allow these and other inputs to be purchased by farmers. It is only when developing countries like Nigeria take such systematic steps before they can attain the agricultural utopia known as ‘Green Revolution’.

Phosphorus is a nutrient with a very good residual value, especially when applied as ground phosphate rock such as Crystalizer (2). When there is adequate soil phosphorus, the level can be maintained by keeping the phosphorus balance (amount applied minus amount removed) positive. Finely ground PRs of medium to high reactivity are suitable for direct application on acid soils giving a long-lasting effect of P and Ca provided that sufficient PR is applied. The application of reactive PRs’ can be considered as a capital investment because of the residual effects of the large amounts of P and Ca that are applied. For the purpose of capitalizing the soils a once in three to four years application of large doses is recommended. Following this regime, two to three times the recommended rates are applied.

The question of applying phosphate fertilizer as a capital investment has been, ‘who pays for the investment’? In answering the question there is the need to consider a similar investment. When a country needs irrigation, it does not ask farmers to build the dams.

The country builds the dam and provides the water. Then the farmer goes to the land, and pays for the water. He pays the privileges that the investment provides. As it is with the dam, the application of phosphorus in Crystalizer or other forms of ground phosphate rock as a capital investment is to provide the capacity of the soil to react more favourably to the soluble fertilizers and other technologies that will be put in the soil. Nigeria’s unique vantage position in actualizing the proposal:
Nigeria has phosphate rock deposits in four sedimentary basins, one of which is located in Sokoto basin. A few Nigerian companies have started using the mineral to manufacture P-based fertilizers such as Crystalizer. Crystalizer is a homogenous blend of ground Sokoto Phosphate rock and mineral magnisite. It contains most of the plant essential nutrients and trace levels of other metals. It is acid free with trace amounts of heavy metals as impurities and therefore environmentally friendly. It is a fertilizer by virtue of its ability to supply P and an ideal soil amendment by virtue of its having calcium, magnesium, organic matter and silicon.

The application of calcium to soil has three effects: it supplies calcium as a plant nutrient, induces an increase in soil pH and engenders better soil structure. The second role as a liming material becomes very important in acid soils where soil pH is corrected for optimum uptake of plant nutrients.