Effect Of Precipitation Effectiveness Indices On The Yield Of Some Selected Cereal Crops
Agriculture in Nigeria is mainly dependent on rainfall which is variable in nature. Therefore, the need to have a full knowledge of its pattern and trend is pertinent in order to achieve food sufficiency. This study examined the effect of precipitation effectiveness indices: Onset date, cessation date, length of rainy season and occurrence of pentad dry spells (5, 10 and ≤15) days on the yield of millet, sorghum, rice and maize in Sokoto State, between 1993 and 2008. Walter‟s 1967 method was used to derive the selected precipitation effectiveness indices while dry spell parameters, was derived in pentads. Crop yield data in (ton/ha) and the selected precipitation effectiveness indices wereharmonised using log10 method. Trendline and linear trendline equations where fitted to show the direction of change. While simple correlation was used to analyse the relationship between crop yield and the selected precipitation indices. Furthermore, regression analysis was used to determine to what extent the selected precipitation effectiveness indices influence the yield of the selected crops. The findings revealed that the trend of these precipitation effectiveness indices are characterized by marked “noises” and variability.
Additionally, onset dates of rainfall are arriving earlier while cessation dates are arriving latter. Consequently the length of rainy season is increasing. Dry spells of 5 days is common while dry spell incidents of 10 days and ≤15 consecutive days is decreasing. Similarly rice and maize yield are increasing, due to early onset date of rains. The regression summary shows that the selected precipitation effectiveness indices account for only 52.1%, 50.4%, 52.1% and 68% of yield variation in maize, millet, rice and sorghum respectively. The study therefore, recommends government support for farmers to increase the cultivation of rice and maize in the study area, and the introduction of more crop varieties that are tolerant to dry spells of 5 consecutive days.
1.1 Background to the Study
The limit to the productive capacity of land resources are set by climate, as climatic variability constitutes a major constraint to agricultural production especially in developing countries. However, adequate knowledge of climatic parameters minimizes climatic constraint to food production (Farajzedah et.al., 2012).
The world population is projected to continue increasing well into the present century. The primary question is whether and how global food production may be increased to provide for the population expansion. It will be necessary to increase current level of food production more than proportional to the population growth so as to meet human demand in food production. The major source of water available either for agriculture or for human consumption is the rain that falls on the Earth Surface. Subsequently, the primary source for agricultural production for most of the world is rainfall. Hence, a detailed knowledge of the rainfall at a place is an important prerequisite for agricultural planning and management. More so, for rain-fed agriculture, rainfall is the single most important Argo-meteorological variable influencing crop production in the tropics (Ravindran, 2010).
The most important characteristics of rainfall are, Onset Date (OD), Cessation Date (CD), Length of Rainy Season (LRS), Mean Annual Precipitation (MAR), Hydrological Ratio (HR), number of Rainy Days (RD), Rainfall Intensity (RI), Specific Water Consumption (SWC), rainfall in months of the growing season (May, June, July, August and September), Seasonality Index (SI), Index of Replicability, and Pentad Dry Spells. These are referred to as precipitation effectiveness indices. However, in spite of voluminous data on weather, all is not yet known that, should be known about rainfall. Therefore, to have a comprehensive inventory of knowledge on rainfall, for agricultural purposes in any space, this must include information concerning the aforementioned characteristics, all of which denote the degree of utility of rainfall (Pashiardis, 2011).
According to Moncunill (2006), precipitation effectiveness indices are indispensible in the measurement of the quantity and period of available moisture utilized by plants, which is essential in appropriate crop selection for planning. In Nigeria, agriculture employs about 70% of the population. Apart from the socio-economic problems facing Nigerian farmers, crop production is predominantly anchored on rain-fed agriculture. Subsequently unreliable amount and spread of rainfall, has been implicated as a major factor leading to Nigeria‟s declining crop production and productivity.
Consequent upon this, a declining amount of rainfall portends an adverse effect on crop production. Hence, an in-depth knowledge and understanding of the pattern of precipitation effectiveness indices is pertinent as it governs and determines crop yield. On this premise a detailed knowledge of precipitation effectiveness indices is an important prerequisite to combating food shortage and rising food prices which have precipitated hunger and starvation in our nation in spite of the abundance of vast acreage of arable land (Audu, 2012).
Interestingly, cereals form the major source of food for human consumption globally. Bezadih, Falco and Yesuf (2011), identified that cereal production is the key to feeding the growing human population. They further asserted that 80-100 million additional people must be supplied with cereal each year which will require a 70% increase in production over the next 30 years. Cereal growing areas are also being reduced by the growth of urban centers as less developed nation enter the industrial age, and finally as these less developed countries gain in affluence, they will demand more meat which will require more cereal for livestock feed. As cereal becomes scarce, and more expensive, the need to increase cereal production becomes more glaring. In recent times Nigeria has faced a rise in food prices, especially cereals. According to Audu (2012), cereals are one of the most important crops grown in the Savanna region of Northern Nigeria, Sokoto State inclusive. Crops like rice, millet, sorghum and maize are the major staple food of most Nigerians, which equally form a major commodity in the interstate trade in the country.
These cereals are important crops cultivated in the Savanna region of Nigeria. They have been in the diet of Nigerians for centuries. They form the staple diet of the people with delicacies like “fura”, “akamu”, “kwokwo”, “kunu”, “tuwo”, “jellof rice”, “white rice”, “agidi” and “utara”. Hence, they are major food crops. The ban imposed by the Federal Government of Nigeria on the importation of these cereals, has occasioned a low supply for them.
Subsequently, local production has to be increased in order to meet demand for human consumption, livestock feeds, baby cereals and pharmaceuticals. Furthermore, the adequate sunshine and moderate rainfall in Northern Nigeria, favour post harvest preservation conditions for these cereals. (Iken and Amusa, 2004). Since, crop production in Nigeria is highly rain-dependent, definitely, information generated on precipitation effectiveness indices will be of considerable agronomic relevance for efficient planning and management of these grains in Nigeria at large and the study area in particular.
1.2 Statement of Problem
Rainfall in Nigeria is the most variable climatic element both in its spatial and temporal distribution (Yusuf and Mohammed, 2011). Living organisms (both plants and animals including Man) cannot survive without optimal water supply. Although, it has been argued that rain fall and temperature are the most important climatic determinants of crop survival and production especially in Nigeria, however, generally; temperature has remained favorable especially during the growing season, on the other hand, the amount, distribution and reliability of rainfall appear the severest constraints to agriculture in Nigeria (Audu, 2012). Following the high dependence on rain-fed agriculture, climatic variability has led to so many incidents of crop failures with its attendant socioeconomic problem. Consequently, since rain-fed agriculture relies on the “mercy of nature”, the need to have a comprehensive knowledge of its pattern and trends is inevitable.
During the eighteenth century, a prominent British economist Thomas Malthus first put forth the observation that population grows exponentially, while food production only grows arithmetically until it reaches some upper limit dictated by the amount of arable land. In order to avert this grim prediction by Malthus, climate must be efficiently, utilized to maximized food production. Furthermore, precipitation effectiveness indices highlight the nature of drought incidents, to engender adequate planning and preparations by farmers. According to Otun (2010), it gives the first indication of drought over an area, better still, the drought characteristic lumped, hidden or entirely omitted by one index, would be better revealed or earmarked by another index. Equally, it is not so much that amount of rainfall that matters, what matters most is how well spread it is. For instance, a delay in the onset of rains may result in poor seasonal distribution, even when that total amount of rainfall received within the same season is normal. Similarly, a pre-mature cassation may constitute a serious water deficit problem. A worse condition may be obtained when the onset is delayed and the rains cease pre-maturely resulting in shortened rainy season duration.
Various studies (Olaniran and Babatolu, 1987; Adebayo and Adebayo, 1997; Abdulhamid and Abubakar. 2002; Sawa and Abdulhamid 2011; Sawa and Adebayo, 2011; Danladi, 2012;Audu, 2012) have been carried out on precipitation effectiveness indices and crop production, in some parts of Nigeria. Olaniran and Babatolu (1987), discovered that pre-sowing rainfall is significantly correlated with the yield of Sorghum and Maize. The result of Adebayo and Adebayo (1997),reveals that hydrologic ratio, onset dates, length of rainy season, dry spell, rainfall in May and June have significant relationship with rice yield, accounting for 73.5% of the variation in the yield of upland rice in the area.
Furthermore, the study of Abulhamid and Abubakar (2002) found the area to have a high hydrologic ratio and low seasonally index due to long dry season of at least seven months. Muncunill (2000), identified that precipitation constitute a major limiting factor for grain yields, and are often associated with small rainfall anomalies. Sawa and Ibrahim (2011), developed “forecast models for the yield of millet and sorghum in the semi arid region of Northern Nigeria using dry spell parameters.” Their findings indicate that dry spells during the growing season is critical to millet and sorghum yield, as the occurrence of dry spells at some phonological stages of development of sorghum is beneficial and increase its yield.
Sawa and Adebayo (2011), considered the impact of climate change on precipitation effectiveness indices in Northern Nigeria and noticed the decrease in length of rainy season, as northern Nigeria gets drier, the rainy months get fewer and dry spell incidents are on the increase, posing an imminent threat to crop production in the region. Similarly, Danladi (2012), looked at precipitation effectiveness indices and millet yield in two local government areas of Kura and Dambatta in Kano State, his findings indicate that precipitation effectiveness indices greatly influence variations in the yield of millet in the study area . In the same vein, Audu (2012),found that a strong relationship exists between precipitation effectiveness indices and crop yield. He further asserts that the frequent dry spells occasioned by late onset, early cessation and fluctuations lead to crop failure. He therefore proffered the early cultivation of crops, especially those which can tolerate long period of absence of rain.
To the best of the researcher‟s knowledge, however, few studies e.g. Sawa and Adebayo (2011), have been carried out on the impact of precipitation effectiveness indices such as Onset, Cessation, Length of rainy season, number of rainy days, Hydrologic Ratio, Seasonally Index, Dry Spell etc on maize, millet, rice and sorghum yield in Sokoto State. This study therefore, seeks to fill this existing gap in relating the yield of these crops to Onset, Cessation, Length of Rainy Season, and occurrence of dry spell of 5, 10 and 15 pentads.
1.3 Research Questions
What are the trends of the selected precipitation effectiveness indices in Sokoto State?
- What is the trend of millet, sorghum, rice and maize yield in Sokoto State?
- What is the relationship between the yield of these selected crops and the selected precipitation effectiveness indices in the study area?
- Which indices has the most effect on the yield of each of the selected crops.
1.4 Objectives of the Study
The aim of this study is to examine the effect of precipitation effectiveness indices: onset date, cessation date, length of rainy seasons and occurrence of dry spell of 5, 10 and 15 pentads, on millet, sorghum, rice and maize yield in Sokoto State, between 1993 and 2008.
The specific objectives to achieve this aim are to:
- Examine trends in the selected precipitation effectiveness indices in Sokoto State between 1993 to 2008
- Assess the yield pattern of millet, sorghum, rice and maize within the stated period
- Examine the relationship between the yield of these crops and the selected precipitation effectiveness indices in Sokoto State
- Identify which indices has the most effect on the yield of the selected crops.
1.5 Scope of the Study
In terms of the spatial extent, this study will be limited to Sokoto State while the content, scope, will include relationship between precipitation effectiveness indices from 1993 to 2008, and yearly yield in tons per hectare of millet, sorghum rice and maize within the same period. This temporal scope is occasioned by lack of crop yield data beyond the stated period from the Sokoto Agricultural Development Project (SADP).
1.6 Significance of the Study
Food is very necessary for human survival. More so, grain production is the key to feeding the ever swelling human population (Bezadih, Falco and Yesuf, 2011). Similarly rainfall pattern in the tropics is highly variable, due to its patchy nature. Therefore, to optimally produce thisselected crops namely: maize, millet, rice and sorghum in the study area, there is the need to fully understand the rainfall patterns and trends.
1.7 Organization of the Study
The study comprises of five chapters. Chapter one consists of the background to the study, statement of the problem, purpose of the study, objectives, research questions, significance, limitation of the study, delimitation of the study, basic assumptions, definitions of key terms and organization of the study. Chapter two comprises of literature review theoretical and conceptual frameworks. Chapter three deals with research methodology, covering research sampling, procedures, research instruments and their validity and reliability, procedures for data collection and data analysis. Chapter four comprises of findings and discussions which were generated by the study. Chapter five presents summary, conclusions and recommendations.
Summary, Conclusion and Recommendations
5.1 Summary of the Study
The major source of water available either for agricultural or human consumption is precipitation. This is the reality in northern Nigeria and the study area in particular where the ultimate productivity of crops under natural conditions are determined by the amount, distribution and variability of rainfall.
The study used daily rainfall records (mm) and crop yield data for maize, millet, rice and sorghum in (ton/ha) sourced from the National meteorological agency (NIMET) in Oshodi Lagos and the Sokoto Agricultural Development Project (SADP), from 1993 to 2008. The relationship between crop yield and the derived precipitation effectiveness indices where analyzed using simple correlation and regression techniques.
Furthermore, the Walter‟s 1967 method was used to derive the selected precipitation effectiveness, indices, while dry spell parameter where derived in pentads (5, 10 and ≤15 consecutive days).Similarly, the yield data for the selected crops and the selected precipitation effectiveness indices where harmonized using the log10 method. While simple correlation was used to analyze the relationship between crop yield data and precipitation indices. In the same vein, regression analysis was used to determine to what extent the selected precipitation effectiveness indices influence the yield variation of the selected crops and which indices have the most influence for each crop.
While, trendline and linear trend line equations was used to show the pattern of the selected precipitation effectiveness indices and crop yield in the study and within the period under review. The result showed that onset dates, cessation dates, length of rainy season, dry spells of 5, 10 and ≥15 consecutive days are characterized by inter-annual variability for example, onset ranges from 3rd July in 1999 to 7th May in 2004, showing a marked distinction of almost two month between these dates. For cessation dates it fluctuates from August 29th in 1997 to September 29th in 1997. Similarly, for LRS it ranges from 74 days in 1999 to 128 days in 2005. For 5 days dry spell it has 5 incidents in 2000 and none in the years preceding 1996.
For 10 days dry spell, its highest level of occurrence which is twice was in 1993 and 1995 while most of the years had none except 1994, 1997, 1998, 2000 and 2004 which all had single incidents. For 15 consecutive days, most of the years had no incident except 1997, 1999, 2000 and 2007 which all had single incidents. These clear pattern of inconsistency and variability for these elements, in Sokoto will have serious implication on grain production as farmers in the study area would find it difficult to predict the selected precipitation effectiveness indices in the area, thereby adversely affecting crop yield and other crop cultivation processes like land preparation, clearing, planting, weeding harvesting and storage.
Additionally, the study revealed that onset dates of rain is arriving earlier than usual, and cessation date of rains is arriving letter than usual. This development, has translated into a longer length of rainy season in the study area, this mean more available moisture for optimal crop yield. Following the regression summary for each crop, the selected precipitation effectiveness indices accounts for only 52.1%, 50.4%, 52.1% and 68.0% variations in the yield of maize, millet, rice and sorghum respectively. Similarly considering the simple correlation analysis between the selected cereals and the precipitation effectiveness indices table 4.3 revealed that rice and maize yield are influenced by early onset, subsequently as onset date of rain arrives earlier in recent times, there is significant increase in rice and maize yield as shown in figures 4.7 and 4.9. The result equally showed a high incident of dry spell of 5 consecutive days in the study area, while dry spells of 10 and ≤15 consecutive days are on the decline.
Based on the findings of the research, it was concluded that there is early onset of rains and late cessation of rains in the study area. Furthermore, rice and maize yield are increasing due to early onset of rains. Finally, there is increase in dry spell of 5 consecutive days, in the study area.
Following the findings and conclusion made in the study between 1993 and 2008, the following recommendations are made:
Since the characteristics of rainfall onset and cessation dates, length of rainy season and dry spells of 5, 10 and ≤15 consecutive days are inconsistent and variable in the study area. It is therefore recommended that land preparation and planting of maize, millet, sorghum and rice can be done from 11th of June, which is the established mean onset date of rainy season in the study area.
Following the early onset of rains and late cessation of rains in the study area, which has led to increase in rice and maize yield, government at all levels should encourage the cultivation of these crops by giving farmers incentives and loans to boost the local production of these crops.
Since there is a high incident of dry spells of 5 consecutive says in the study area, farmers should introduce other crops and seed varieties that can tolerate short dry spells in order to boost crop production in the study area.
Finally, more research should be carried out on other areas not considered by the research work, concerning cereal production in the study area.
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