Effect of Agricultural Waste and Inorganic Fertilizers on Polluted Soil

Effect of Agricultural Waste and Inorganic Fertilizers on Polluted Soil

Chapter One

Research Objectives

The general purpose of the study was to promote soil productivity in acidic soils thus improving food security. The study sought to address the following specific objectives:

To determine the effect of agriculture waste, and inorganic fertilizer on polluted soil in Akwa Ibom State.
To evaluate the effect of agriculture waste and inorganic fertilizer on maize growth and yield in Akwa Ibom State.
To assess the profitability of agriculture waste and inorganic fertilizer in the production of maize in Akwa Ibom State.

CHAPTER TWO

LITERATURE REVIEW

General overview

Soil pollution has been reported as the main limitation to crop growth in the tropical region (Busari et al., 2008). The tropical land that was one time productive has been reported to be infertile due to consistent farming and erosion causing physical soil destruction, low organic matter and a decline in cation exchange capacity (CEC) as well as increased manganese (Mn) and aluminium (Al) toxicity (Kafle and Sharma, 2015). Other than Al and Mn toxicity, deficiencies of calcium, magnesium, and phosphorus in the soils are also considered as other significant constraints that limit plant growth on acidic soils (Liao et al., 2006).

The agricultural sector is constrained by low available soil nitrogen and available phosphorus due to high soil pollution that results in low crop yield in both commercial and small-scale farms (Sanchez and Jama, 2002; Kisinyo, 2012). In Nigerian highlands, most of the improved maize germplasm and land used by farmers are responsive to the high exchangeable Al (>2 cmol kg^-1) and high (>20%) Al saturation commonly encountered in many acidic soils (Kifuko et al., 2007).

Soil pH and pollution

The soil pH varies with amount of H⁺. The more the high H⁺ in the soil solution, the higher the pollution while less H⁺influences the soil to be alkaline and when moderate the soil is said to be neutral. The pH less than 7 indicates the degree of soil pollution and greater than 7 indicates the increase in the soil alkalinity level (Tan, 2010). The soil with pH less than 4.4 are considered exceedingly acidic, 4.5 to 5.5 strongly acidic, 5.5 to 6.0 are moderately pH, and 6.1 to 6.5 are considered slightly acidic (Kanyanjua et al., 2002). Table 2.1 shows the classification of soils based on the soil pH.

Soil pH is an important soil chemical property that indicates the quality of the soil. It is important to understand the soil pH to ensure proper soil management and optimal crop productivity. Tentatively, soil pollution is quantified on the basis of aluminium (Al³⁺) and hydrogen (H⁺) concentrations of soils (Fageria and Baligar, 2008). Soil pollution involves the amount of H⁺in the soil solution and occurs when there is a build up of acid-forming elements in the soil. Soil pollution is related to high aluminium (Al), hydrogen (H), manganese (Mn) and iron (Fe) toxicities in plant roots (Fageria et al., 2008). Also is related to deficiencies of plant available including K, P, and (Ca) among others (Wood, 1993). Low soil pH has a high amount of Fe and Al oxides with corresponding deficiency of Phosphorus in the soil solution (Kanyanjua et al., 2002) which negatively affect soil fertility and productivity (Muindi et al., 2016). The decrease in the pH level of the soil is associated with a decline in the availability of plant nutrients such as phosphorus, potassium, and nitrogen. In highly acidic soils, phosphorus is particularly sensitive and becomes a limiting nutrient to the soil (Harun et al., 2005). Also decline in the soil pH stimulate presence of phytotoxicity substances, e.g. Mn and Al resulting in acidic soil infertility thus limiting crop production (Proietti et al., 2015).

Causes of soil pollution

Soil pollution maybe as a result of the natural process caused by acidic parent materials, the decay of organic matter and leaching by rainfall (Havlin et al., 2005) making soils to be inherently acidic especially in areas with high rainfall (McCauley et al., 2009). The differences in parent material chemical composition, soils becomes more acidic within a prolonged period of time (Rowell, 2014). Thus, soils developed from limestone or calcareous rocks are less acidic than those developed from granite material. Organic matter decay produces H⁺ that is responsible for pollution in the soil, though it forms a weak acid the effects in the soils accumulate over many years (Thapa, 2015). On the other hand, excessive rainfall causes soils to become acidic over a long time through continuous removal of basic cations in the soils (Reuss and Johnson, 2012).

CHAPTER THREE

MATERIALS AND METHODS

Experimental Design

The experiment was laid out in a randomized complete block design (RCBD) with eight treatments replicated in ten farms. The farmers’ fields were selected based on soil pH, size of the land, terrain and tree cover. The experiments were conducted during the short rains season lasting from October to December 2016 and long rains season from March to May 2017. The plots were 4.5 m by 4 m and were demarcated after ploughing maintaining a guard row of 1 m from one plot to another. Maize hybrid H516 was used as the test crop. The treatments comprised application of agricultural lime (calcium carbonate), manure and mineral fertilizer (Table 3.3).

Soil Sampling

Soil samples were obtained from all plots using an Edelman auger at a depth of 0-20 cm. The initial sampling was done before setting up the experiment (July 2016). Sampling was also done after the harvest of the first season (Short rains periodJanuary 2017) and then after the end of the experiment (Long rains period-July 2017).

The samples were taken randomly at five different points using the zigzag method

(Santos et al., 2017) and then mixed thoroughly to a composite sample. The composite samples were labelled, packed and taken to laboratory for chemical analyses during all the sampling intervals.

CHAPTER FOUR

RESULTS AND DISCUSSION

Rainfall

The distribution of rainfall during the study period varied between the seasons. Cumulatively, 2017LR received higher rainfall amounts than 2016SR. The total rainfall recorded in 2016SR and 2017LR was 455 mm and 967 mm, respectively

(Figure 4.1). There was soil moisture deficit for most of the growing season during 2016 SR, with more than 80% of the rain being received in the first month followed by a prolonged dry season. This adversely affected crop yields.

CHAPTER FIVE

SUMMARY, CONCLUSIONS AND RECOMMENDATIONS

Summary

During the two seasons under study application of 2 t ha^-1 lime plus 10 t ha^-1 manure recorded the highest increasein soil pH during 2016SR (4.61 to 5.21) while in 2017 LR, sole lime had the highest increase from 4.51 to 5.28. This is an increase of 13.02% and 17.07%, respectively over the initial soil pH. This was closely followed by 2 t ha^-1 lime with 5 t ha^-1 of manure plus 30 kg P₂O₅ ha^-1 as P fertilizer with 15.3% reduction in soil pH in 2017LR. In comparison with treatment with sole fertilizer, lime and manure treatments had the highest reduction in soil exchangeable pollution.

The influence of the treatments on maize height, chlorophyll content, stover and grain yield was consistent. Application of 2 t ha^-1 lime with 5 t ha^-1 of manure plus 30 kg P₂O₅ ha^-1 had the tallest plants of 232.83 cm and 296.13 cm in 2016SR and 2017LR, respectively. Similarly, this treatment recorded the highest chlorophyll content of 53.13 SPAD units followed by lime combined with fertilizer by 52.11 SPAD. The highest stover and grain yield was attained with application of combined agriculture waste plus fertiliser.

Generally, the economic returns were low, with negative net benefits and benefit-cost ratio of less than 1. Lime plus fertilizer had the highest net benefit of 128.75 USD in the 2017LR. The treatments with inorganic fertilizers had the highest BCR in 2017LR due to the low labour input required.

Conclusions

Treatments with lime and manure, sole or combined had a significant increase in soil pH which increased the availability of soil nutrients. Application of combined agriculture waste and fertilizer lime had the highest stover and grain yield compared to those with sole manure, fertilizer, or lime. This is demonstrating the superiority of integrated soil fertility management in yield improvement. This indicates that liming is an effective method of ameliorating soil pollution and offers a better option for increasing maize yields in degraded soils of central highlands of Nigeria. Economic returns were significantly affected by interaction of agriculture waste and P fertilizer where treatment applied with fertilizer had more benefit compared to those with no fertilizer.

Recommendations

Based on the findings the following recommendations were derived:

For improved soil pollution and increased maize yields, smallholder farmers should adopt integrated application of manure with lime and P fertilizer.
Farmers need to consider economic returns when selecting agricultural production technologies to use.

Areas of further research

A long-term study needs to be considered using other types of lime (Calcium Oxide and granulated lime) and manure to evaluate change in soil pollution and effect on maize yield and profitability.
Further research should be conducted to explore more rates of lime, different types of lime and their effects in long-term to determine the optimum liming level of different types of lime for acid soils.
Further research to assess the economic return in the long-term use of agriculture waste and fertilizer is suggested.

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