**1.1. Declining soil fertility in low input agriculture**

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 bil‐ lion U.S. dollar in fertilizer in 37 African countries over three decades. Due to large quanti‐ ties 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 applica‐ tion 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 sys‐ tem 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.

© 2012 Fukuda et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Fukuda et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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 bio‐ mass 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 live‐ stock feed and fuel so leaving crop residues in the field is seldom. Even though, incorpora‐ tion 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 approxi‐ mately 20 percent of N and P, and most K relative to the needs of applied chemical fertiliz‐ ers in the Northern region of Ghana where rice cultivation is the most prominent.

rather than only dependence on P cycling through organic-based system. However, P fertil‐ izer management became more difficult because the only natural P source *i.e.* phosphate rock (PR) for manufacturing P chemical fertilizers is non-renewable and finite resource. Though, ground PR can be directly used as P fertilizer but it slowly releases P in acid soils

Alternative Fertilizer Utilizing Methods for Sustaining Low Input Agriculture

http://dx.doi.org/10.5772/53578

227

Phosphate rock, a natural form of mineral apatite contains not readily phosphate content for plant. Phosphate rock must be treated to convert phosphate to water soluble of plant availa‐ ble forms [11]. Major solid water soluble P fertilizers are single superphosphate (SSP), triple superphosphate (TSP), monoammonium phosphate (MAP), and diammonium phosphate (DAP). In fully acidulated commercial grade P fertilizers, SSP is made by adding sulfuric acid to PR. Triple superphosphate containing about 2 times of P concentration as SSP, is made by adding phosphoric acid to PR. Ammonium phosphate fertilizers are produced by passing amnonia through phosphoric acid. The compounds of P within water soluble frac‐ tion are mainly in the forms of monocalcium phosphate or MCP [Ca(H2PO4)2.2H2O] in SSP and TSP, NH4H2PO4 in MAP, and (NH4)2HPO4 in DAP in which over 90% of total P concen‐ trations are water soluble P [12,13]. Diammonium phosphate, MCP, and TSP can be account‐

Continuous mining PR and increasing use of P chemical fertilizers might not be responsible management of resource use. More efficient uses of P fertilizers in agriculture have been paid intention. Phosphorus efficient plants are recently developed through plant breeding or genet‐ ic modification, but more P efficient plants which are modified root growth and architecture, manipulated root exudates, or managed plant-microbial association such arbuscular mycor‐ rhizal fungi and microbial inoculants are not common, and still have less potential trade-off [14]. So far, fertilizer management still has a significant contribution to overall agricultural crop production, household's farming system, farmers, and the rural poor [4]. In addition, the po‐ tential of genetically improved crops cannot be achieved when soils are depleted of nutrients. Sanchez [1] stated that improved crop varieties have responsible for only 28% yield increases in Africa, but 66-88% in Asia, Latin America, and the Middle East when rates of adoption for new improved varieties have been similar during the last four decades. Therefore, it is necessity to find alternative fertilizer utilizing methods to increase and sustain crop yield in low input agri‐

This work gathered information from published papers (secondary data) focusing on the utilization of small quantity of fertilizer to boost crop productivity in wide-range of cli‐ mates and soil conditions. The effective methods have been revealed including 1) fertilizer microdose application, 2) addition of small amount of fertilizer to the seed by coating, 3) increase of nutrient concentration in seedling by soaking in, or dipping seedling in the nu‐ trient slurry. Moreover, two experiments were conducted to investigate the effects of fertil‐ izer seed coating and fertilizer seedling soaking on the early growth of rice (*Oryza sativa*

resulting in gradual build up P in numbers of cropping season.

ed as a half of phosphate-based fertilizer applications worldwide [11].

culture and these methods should be affordable for local farmer.

**2. Materials and methods**

cv. IR74) grown on acidic P deficit soil.

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 trop‐ ical regions. Besides, improved fallows have not been proved yet on their benefits in semiar‐ id 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 resi‐ dues which in turn control the nutrient release rates. Tian et al. [7] found that the contribu‐ tion 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 Pa‐ leustalf soil in Nigeria.

Animal manures from poultry, pig, cow, goat, and sheep contain all the major nutrients. These manures are very good materials for improving soil fertility and crop productivity [8,3]. Tobita et al. [6] reported that if only 20 percent of total livestock organic resource esti‐ mated in Ghana was utilized, so it could replace the requirement for chemical fertilizer in rice cultivation system entire the Northern region. However, gathering bulky dung of live‐ stocks or excreta (dung and urine) from grazing livestock was difficult particularly in rural area where these manures are not sold and scarce [9]. Unlikely, poultry manure may be val‐ id in urban center where intensive production of poultry has being implemented. In present, poultry manure is on high demand but its quantity is not enough for farmer's need resulting farmers have to pay in advance before manure will be delivered to the field [3,10].

#### **1.3. Alternative P fertilizer utilizing methods**

Many soils in sub-humid and humid tropics including SSA have very low levels of natural P, thus P fertilization is essential for maintaining desired level of crop yield. Buresh et al. [2] indicates that input of P fertilizers is required to replenish P stock in highly P deficient soils rather than only dependence on P cycling through organic-based system. However, P fertil‐ izer management became more difficult because the only natural P source *i.e.* phosphate rock (PR) for manufacturing P chemical fertilizers is non-renewable and finite resource. Though, ground PR can be directly used as P fertilizer but it slowly releases P in acid soils resulting in gradual build up P in numbers of cropping season.

Phosphate rock, a natural form of mineral apatite contains not readily phosphate content for plant. Phosphate rock must be treated to convert phosphate to water soluble of plant availa‐ ble forms [11]. Major solid water soluble P fertilizers are single superphosphate (SSP), triple superphosphate (TSP), monoammonium phosphate (MAP), and diammonium phosphate (DAP). In fully acidulated commercial grade P fertilizers, SSP is made by adding sulfuric acid to PR. Triple superphosphate containing about 2 times of P concentration as SSP, is made by adding phosphoric acid to PR. Ammonium phosphate fertilizers are produced by passing amnonia through phosphoric acid. The compounds of P within water soluble frac‐ tion are mainly in the forms of monocalcium phosphate or MCP [Ca(H2PO4)2.2H2O] in SSP and TSP, NH4H2PO4 in MAP, and (NH4)2HPO4 in DAP in which over 90% of total P concen‐ trations are water soluble P [12,13]. Diammonium phosphate, MCP, and TSP can be account‐ ed as a half of phosphate-based fertilizer applications worldwide [11].

Continuous mining PR and increasing use of P chemical fertilizers might not be responsible management of resource use. More efficient uses of P fertilizers in agriculture have been paid intention. Phosphorus efficient plants are recently developed through plant breeding or genet‐ ic modification, but more P efficient plants which are modified root growth and architecture, manipulated root exudates, or managed plant-microbial association such arbuscular mycor‐ rhizal fungi and microbial inoculants are not common, and still have less potential trade-off [14]. So far, fertilizer management still has a significant contribution to overall agricultural crop production, household's farming system, farmers, and the rural poor [4]. In addition, the po‐ tential of genetically improved crops cannot be achieved when soils are depleted of nutrients. Sanchez [1] stated that improved crop varieties have responsible for only 28% yield increases in Africa, but 66-88% in Asia, Latin America, and the Middle East when rates of adoption for new improved varieties have been similar during the last four decades. Therefore, it is necessity to find alternative fertilizer utilizing methods to increase and sustain crop yield in low input agri‐ culture and these methods should be affordable for local farmer.
