The enhanced Best Performance Algorithm for the Annual Crop Planning Problem Based on Economic Factors
3.2 Background to ACP Problem
Crop production is a multi-staged process which includes: crop selection, land allocation, planting, crop development, harvesting, crop storage, and the marketing stages (Acquaah, 2004). Ultimately, to achieve maximum returns within a production year, effective decisions need to be made at each stage of the crop production process. Yet, this is no simple task as several stochastic factors affect the crop production process.
Notable stochastic factors include the climatic conditions, soil characteristics, the market demand and supply conditions, and cultivation practices, etc. The climatic conditions primarily include temperature, humidity, wind-speeds and rainfall (Brouwer and Heibloem, 1986). These importantly effect the rates of evaporation from the soil surface back into the earth’s atmosphere. It also influences transpiration through the stomata of the crops.
Soil characteristics are those of soil texture, the soil nutrition, the soil moisture content levels, the rate of transitivity of water through the soil, etc. (Astera, 2010). The content structure of the soil texture influences the soil moisture holding capacity, and the transitivity rate. The soil moisture holding
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capacity is the volume of water that can be contained within the soil. The transitivity rate is the rate at which water is absorbed by the root system of the crop. Soil nutrition is vital for optimal crop growth. Furthermore, concerning the cost of the sale of the harvests, the demand and supply conditions have a major influence (Whelan and Msefer, 1996).
During the crop selection stage (notably the first), several factors need to be considered in determining the most appropriate crops to be cultivated. Firstly, crop selection is location specific. Reason being, crops adapt well to the environmental conditions at specific geographical locations (Mustafa et al., 2011). Also, it is necessary that there be sufficient demand for the crops to be produced in order to be counted profitable; it should also be sustainable for the future production.
Upon the crops having been selected, decisions would thereafter need to be made concerning the resource allocations amongst the various competing crops required to be produced. Resource allocations occur at the land allocation stage of the crop production process. This embeds the scope of the ACP problem.
The intent of the ACP problem is to determine resource allocation solutions amongst the various competing crops which are required to be produced. The limited resources concerned with the ACP problem include land area, irrigated water supply, and the various costs associated with the production of each crop. The objective is to maximize the total gross profits that could be earned from the sale of the harvests at the end of the forthcoming production year.
The ACP mathematical model considers several important factors in determining scalable solutions:
the area of agricultural land available for crop production, rainfall estimates, the Crop Water Requirements (CWR’s) per crop, the irrigated water supply and its cost, the production costs, the crop yields (this is under the assumption of what the yields are expected to be given the previous year’s statistics), the producer prices per crop, and the market demand conditions.
The area of land available for crop production can be segmented into different farm-plot types. Farm- plot types are appropriate for the production of different types of crops. For sequential cropping (which is the current scope for ACP problem), the single-crop farm plots are used to produce all the crops that grow all year around on the same farm plot. These are called perennial crops. Examples include crops such as Lucerne and fruit trees. Perennial crops can be harvested once or several times
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within the year. The double-crop farm plots are likewise used to produce crops that grow in sequence of each other on the same farm plot within the production year. Examples are the summer and winter crop groups. For instance, Maize (being a summer crop) is grown in sequence with Wheat (being a winter crop) on the same farm plot within a production year in South Africa. Similarly, triple-crop farm plots are used to produce three crop groups that grow in sequence of each other on the same farm-plot, etc. Sequential cropping is a highly beneficial cultivation practice: it yields higher returns per farm plot; it provides additional protection against pests, bacteria and weed development; it adds to the nutritional value of the soil, which in turn reduces fertilization and pesticide costs (Charles, 1986).
Each crop cultivated additionally differs in CWR needs. The CWR need of each crop differ due to the diversity in crop characteristics. It also differs due to the fact that the CWR need of the same crop grown at different geographical regions may differ due to the differences in the climatic conditions.
The difference between the CWR need of each crop and precipitation is the volume of irrigated water that is required for optimal crop growth throughout its lifespan.
The scheduling of irrigated water for the production of each crop is out of the scope of this study.
However, the feed of fresh water supply, by either rainfall or irrigation to the crops root system need to be well planned throughout the different stages of crop development. For example, a fully grown crop would require more supply of water than a newly planted crop. Also, water supplied to the surface of the crops root system would need to be in accordance with the moisture content level of the soil. The moisture content level should ideally be maintained between wilting point and field capacity; field capacity is the maximum water holding capacity of the soil. At any volume greater than the field capacity, the crop is susceptible to root damages. Also, at any level below wilting point, the crop will no longer be able to absorb water in order to survive (Brouwer and Heibloem, 1986). If a crop suffers water stress, such as mild, moderate or severe, it will affect the physiological processes of respiration, growth, photosynthesis and reproduction within the plant. Therefore, in order to achieve the ideal water balance within the plant for optimal growth and yield, it is essential that the soil moisture content be maintained throughout the lifespan of the crop. Herein lies the importance of irrigation.
Irrigated water is primarily extracted from ground water reserves such as rivers and lakes. In being supplied to the irrigation schemes, it is accompanied by a water charge m-3 of the water utilized.
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Production costs, coupled with crop yields and producer prices determine the profit earned. This is also in accordance with the market demand of the crop. Production costs consist of the fixed and variable costs of production. Fixed costs relate to the financial outlay irrespective of production. Fixed costs include loan repayments and other types of monthly expenses incurred in order to facilitate the crop production process. Variable costs are the costs incurred in the production of a unit of the harvest.
Variable costs include that of tilling the soil, labour costs, the costs of soil nutrition, pest control, irrigated water supply costs, and harvesting costs, etc.
Production costs will differ per crop produced. This is due to crop specific cultivation practices, and the cost of it. A simple example is the cost of harvesting a crop by hand, and harvesting a crop using machinery. In harvesting using these two different ways, the costs will differ. Cultivation practices also affect the crop yields (Dukes et al., 2012). Apart from maintaining the soil moisture content level and the nutritional value of the soil, other factors need to be dealt with which will affect the crop yield. These include weeds, pests and bacteria which occur during the lifespan of a crop.
In crop planning, the exact estimates of production costs, yields and producer prices cannot be pre- determined. Rather, statistics from previous years of crop production are used in the ACP mathematical model. These statistics will be used to estimate the figures in attempting to quantify solutions. Amongst others, these statistics can be determined from published literature and/or consultancy services (Kantanantha, 2007). Realistically, the statistics should be location specific. The objective in determining solutions is to advise crop planners on how to better prepare for the production year ahead.