solution of lack of fertilizers in agriculture?
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Answer:
Improvement of soil fertility and plant nutrition to sustain adequate yield of crop is essential since soil degradation has been identified as a major constraint and a root cause of declining crop productivity in many developing countries e.g. Sub-Saharan Africa (SSA). Sanchez [1] reported very high rate of annual depletion for 22 kg nitrogen (N), 2.5 kg phosphorus (P), and 15 kg potassium (K) per hectare of cultivated land or an annual loss equivalent to 4 billion U.S. dollar in fertilizer in 37 African countries over three decades. Due to large quantities of nutrients are removed from soil through crop harvest without sufficient supply of fertilizers and manure causing low input agriculture has been unfortunately implemented by farmers and the consequences of low crop productivity would increase food insecurity. In many regions, local farmers lack of sufficient fertilizer, money for purchase, access to the credit, and transportation resulting to low in fertilizer input and a gradual decrease of soil fertility [2]
1.2. Limitation on replenishing soil fertility and increasing crop yield
Numbers of strategies have been used to restore soil fertility including traditional application of inorganic fertilizers or use of organic fertilizing materials such as plant residues (i.e. rice straw and husk), green manure, and animal manure [3]. Uses of crop management system such as cover crops, legumes, mulching, fallow, and agroforestry are well documented [4]. Moreover, adoption of high yielding and genetically improved crop varieties is a good option for increasing yield productivity.
Amongst ways of soil fertilization, increasing use and continuous application of inorganic fertilizers seemed to be limited because fertilizers in Africa are 2 – 6 times more expensive than that of in Europe, North America, and Asia [1]. Applying plant residue or organic biomass to soil has influenced on soil nutrients, soil physical condition, soil biological activity, and crop performance. However, applying these organic fertilizing materials such as rice straw and husk, green manure or organic biomass (i.e. leaf biomass) to soil are not attractive to farmers compared to straw burning due to short term effects of organic materials on crop yield are often small. Cutting and carrying biomass to the field also require high labor and cost. On other hands, crop residues have high economic value and have been used as livestock feed and fuel so leaving crop residues in the field is seldom. Even though, incorporation of rice straw which is abundant and widely spread in the rice field can return and reserve most of nutrients to soil particularly N, P, K, S, and Si in long term [5]. Tobita et al. [6] and Issaka et al. [3] reported that adding rice straw to rice system could gain approximately 20 percent of N and P, and most K relative to the needs of applied chemical fertilizers in the Northern region of Ghana where rice cultivation is the most prominent.
Crop management such as tree fallow system is not attractive for farmer because they prefer better land use alternative owing to population pressure particularly in the humid and tropical regions. Besides, improved fallows have not been proved yet on their benefits in semiarid tropics of Africa. The potential of fallow system on shallow and poorly drained soil is poor [1]. Growing leguminous plants as fallows before cropping season or intercropping with crop is effective crop management to accumulate N for consecutive crops. However, it should be noted that effects of plant residues on soils and crops depend on the quality (i.e. carbon/nitrogen ratio, lignin, and polyphenol contents) and the decomposition rates of residues which in turn control the nutrient release rates. Tian et al. [7] found that the contribution of low quality plant residues as mulching on maize grain yield and protein concentration was lowest in comparison to intermediate or high quality residues on Oxic Paleustalf soil in Nigeria.