THE EFFECTS OF TILLAGE ON SOIL ORGANIC MATTER
1.1 Background of the Study
Influence of soil quality on crop production and the need to sustain soil quality are crucial to long term sustainability of life in soils. Soil quality is defined as the capacity of soil to function within ecosystem boundaries to sustain biological productivity, maintain environmental quality and promote plant and animal health (Doran and Parkin, 1994). The concept of soil quality refers to more than just vigor of soil biota. It also considers chemical, physical and biological, as well as ecological properties of soils and the disturbance and ameliorative responses by land managers (Sanginga and Woomer, 2009).
Soil quality assessment is vital for proper maintenance and management of natural resources for sustainable and continuous crop production. Hence, the need to adopt good management and land use practices as well as appropriate soil protection strategy and policy. Protection of soil quality under intensive land use and fast economic development is a major challenge for sustainable resource use in the developing world such as Nigeria (Doran and Parkin, 1996). Therefore, the basic assessment of soil quality is necessary to evaluate the degradation status and changing trends following different land use and small holder management interventions (Lal and Stewart, 1995). Development of such a strategy and policy require a careful knowledge of the soil quality status, extent and impact of soil degradation processes and land use management strategy in practice. Soil tillage is among the important practices affecting soil quality and crop yield. It contributes up to 20% of all crop production factors (Khurshid et al., 2006).
Tillage method affects sustainable use of soil resources through its influence on soil quality (Hammel, 1989). Tillage systems; particularly conventional tillage system, adversely affect soil quality by damaging soil structure, decreasing soil moisture content, increasing soil bulk density and root penetration resistance (Rashidi and Keshavarzpour, 2007). Derpsch et al. (2009) reported that continuous cultivation under conventional or intensive tillage leaves soil bare and unprotected, thereby promoting soil structure deterioration and leading to excessive high soil temperature. However, No-tillage system improves the soil’s moisture retention, aeration, infiltration and reduces run off and evaporation (Duiker and Myers, 2005). Also, annual disturbance and pulverization caused by conventional tillage produce a finer and loose soil structure as compared to conservation and no-tillage method which leaves the soil intact (Rashidi and Keshavarzpour, 2007). Soils in the Northern Guinea Savanna of Nigeria are continuously and intensively cultivated, resulting in accelerated soil erosion, soil nutrient depletion and soil degradation (Bationo et al., 2003). The soil supports production of cereal crops, mainly sorghum, maize, millet etc. and out of these crops’ sorghum is one of the most cultivated in the zone. Sorghum is a major staple cereal crop grown mainly for food, fodder and production of alcoholic beverages (Kutama et al., 2010). It is ranked first both in terms of production and total land area put to cultivation of the different staple cereal crops grown in Northern Nigeria (Purseglove, 1972; FAO, 2005; Daniel and Maria, 2009; Ngugi et al., 2002). In 2004, Nigeria was the largest producer of sorghum in Africa and the third most important sorghum producer in the world after United States and India (FAO, 2005; Wikipedia 2008). According to Ofor et al. (2009), sorghum and maize are high-nutrient demanding crops compared with other cereals. These crops require both the major nutrients (N, P and K) and the secondary nutrients (Zn, S, Mg, Ca, B, Fe, Cl, Cu etc.) in adequate amount to ensure good root establishment, vigorous and healthy growth, and increased yield.
However, in Guinea Savanna zone of Nigeria, intensive cropping of this major staple cereal crop and frequent removal of crop residues year-in year-out have adversely affected soil quality and led to nitrogen and phosphorous deficiency in the soils. In view of the nutrient deficient status of the soil, Desmodium, a forage legume, integrated into sorghum cropping system was evaluated in this study. Desmodiun uncinatum is a forage legume capable of increasing the activities of beneficial soil organisms and improving the quality of soils by ―fixing‖ nitrogen and through its incorporation as a residue into the soil. Khan et al. (2008) reported that Desmodium has proven to have beneficial effect on soil fertility, soil erosion control and soil moisture conservation through the returns of crop residues to soil, instead of feeding them to livestock, without necessarily adding inorganic fertilizer and pesticide. The aim of this study therefore was to determine the contribution of Desmodium uncinatum under conservation tillage practices to the yield of sorghum. The study also measured changes in soil quality following sorghum-Desmodium intercropping in two-year cropping seasons in the Northern Guinea Savanna of Nigeria.
1.2 Statement of the Problem
Soils of the Northern Guinea Savanna of Nigeria are continuously and intensively cultivated resulting in soil quality degradation, accelerated soil erosion and soil nutrient depletion. This study on effect of tillage, sorghum/Desmodium intercrop and fertilizer rates on soil quality was conducted in order to investigate the extent to which it can alleviate the afore-mentioned problems in the zone. The study involved a forage legume (Desmodium uncinatum) subjected to different levels of N fertilizer rates (30kgN ha-1, 40kgN ha-1, 50kgN ha-1 and 60kgN ha-1) and P fertilizer rates of (6.6kgP ha-1, 13.2kgP ha-1 and 26.4kgP ha-1), intercropped with sorghum (SAMSORG 14) and planted under different tillage systems viz; (i) conservation tillage system which includes, sorghum/Desmodium incorporated (SDIC),
1.3 Objectives of the Study
The main objective of this study is to determine the effect of tillage on soil organic matter. Specific objectives include:
i. To evaluate the impact of tillage on soil productivity.
ii. To determine soil organic matter retention in the soil.
iii. To find out acceptable soil management practices to enhance productivity.
1.4 Research Questions
i. What is the impact of tillage?
ii. What is the impact of proper soil management practices?
iii. What are the soil management practices on productivity?
1.5 Research Hypotheses
H0: There is no significant impact of tillage on soil productivity.
Hi: There is a significant impact of tillage on soil productivity.
H0: There is no significant impact of soil organic matter retention in the soil.
Hi: There is a significant impact of soil organic matter retention in the soil.
H0: There is no significant impact of soil management practices to enhance productivity.
Hi: There is a significant impact of soil management practices to enhance productivity.
1.6 Significance of the Study
In Africa, three-quarters of farmland is severely degraded (Eswaran, 1997; Stocking, 2003). As a result, Africa (Nigeria inclusive) cannot produce enough food to keep pace with its food needs. Also, Africa’s per capita food production is declining (Lal, 1997; Lal and Stewart, 1995) largely due to poor soil quality. Declining soil productivity due to poor soil quality has been a major limiting factor to food production in Nigeria and in the Guinea Savanna belt in particular (Sanginga et al., 2001; Yusuf et al., 2003). There is also the growing quest to protect soil quality under intensive land use and to adopt good management and land use practices. More so, inorganic fertilizer sources and chemicals are becoming increasingly unavailable to small scale famers due to poor economic policies and poor standard of living of the farmer. Kim et al. (1997) showed that farmers in the Northern Guinea Savanna of Nigeria apply low N-rates of 20 to 50KgNha-1 for sorghum which is too low to improve crop productivity. Hence, other fertility enhancement sources are needed to facilitate sustainable crop production. Desmodium uncinatum, a forage legume that has proven to have beneficial effect on soil fertility, soil erosion control and soil moisture conservation through the returns of crop residues and ―fixing‖ nitrogen into the soil, without necessarily adding inorganic fertilizer (Khan et al., 2008) was intercropped with sorghum in this study and evaluated. Therefore, in an effort to mitigate land degradation and soil nutrient depletion problems in the Northern Guinea Savanna Alfisols, the contributions of Desmodium uncinatum under conventional and conservation tillage practices in improving soil quality and yield of sorghum.
1.7 Limitations of the study
The demanding schedule of respondents made it very difficult getting the respondents to participate in the survey. As a result, retrieving copies of questionnaires in timely fashion was very challenging. Also, the researcher is a student and therefore has limited time as well as resources in covering extensive literature available in conducting this research. Information provided by the researcher may not hold true for all research under this study but is restricted to the selected respondents used as a study in this research especially in the locality where this study is being conducted. Finally, the researcher is restricted only to the evidence provided by the participants in the research and therefore cannot determine the reliability and accuracy of the information provided. Other limitations include;
Financial constraint: Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet, questionnaire and interview).
Time constraint: The researcher will simultaneously engage in this study with other academic work. This consequently will cut down on the time devoted for the research work.