Fundamentals of Irrigation Methods and Their Impact on Crop Production

Abstract

Water is the most precious resource on earth which is the sustenance of life. However, the competition for available water resources has intensified due to climate change and increase in global population. With a significant decrease in freshwater availability for crop production, agriculturists are open to innovation that could help save water and maximize crop production per unit drop of water. To ensure food security of a growing population, crop cultivation practices have continued to incorporate water-saving irrigation techniques to cope with water deficits, and increase crop production in an eco-friendly environment. This chapter discussed the different irrigation types based on driven-force and their specific advantages; fertigation; designing irrigation systems and scheduling of irrigation; water conservation through mulching; and water management for sustainable Integrated Pest Management (IPM). The introduction of water-saving techniques and their successful application has significantly reduced water loss through unproductive outflows and increase water and nutrients use efficiencies thereby promoting crop production. However, to achieve more success in the future, deliberate policy by government on irrigation and immense contributions from scientists would be required.

1. Introduction

Water is the most precious resource on earth and is also the most abundant constituent of most organisms. This implies that most organisms including plants depend on water for their survival. Plants absorb a large quantity of water from the soil for physiological and biochemical processes that transform into growth and development of the plant. The importance of water to crop production made it an essential factor in ensuring food security. The trending issues of climate change resulting in erratic precipitation patterns, and increasing desert encroachment pose a threat to farmers in producing food that will meet the demand of the global population. To ensure food security in a changing world, additional water supply in the form of irrigation is necessary.

The artificial application of water to soil to meet the water need of crops and to maximize production is termed Irrigation. Irrigation systems are of two types based on their driven force (gravity-driven and pressure-driven). Whatever irrigation method is adopted, its purpose is to attain better water management and a higher yield.

2. Gravity-driven or surface irrigation

Gravity-driven irrigation is conventional and has been in use since time immemorial. This approach does not use pumps and relies on the ability of water to move through resistance. The irrigation system is efficient on plain topography for even distribution of water. It has three phases which are the advance, storage, and recession.

The advanced stage is the period of water introduction to the field. Water flows over the field to the end of the field with the help of gravity until the field becomes flooded. However, the storage period is the time frame for water to infiltrate the soil; whereas, the recession period begins after the source of the water is cut off. The water infiltrates the soil more and dries up as a result of evaporation and the closing of the water source. The success of surface irrigation depends on the water holding capacity of the soil, field slope, soil surface roughness, and the shape of the flow cross-section. Examples of surface irrigation include continuous flooding and furrow irrigation (Figure 1).

Figure 1.

Gravity-driven irrigation system: continuous flooding system (A), furrow irrigation system (B).

2.1 Continuous flooding

Continuous flooding is the process of artificially submerging a leveled land under water. It is a system predominantly used for rice cultivation in many regions of the world. Among continents, Asia is ranked the largest producer of rice, and it is responsible for 75% of the total global production. Rice is an aquatic plant but can survive under different soil conditions. However, the introduction of water-saving techniques and the release of drought-resistant varieties continuously prove that flooding is dispensable for rice production. In paddy, the field is irrigated until the water level reaches 5–6 cm above the ground level and is continuously maintained throughout the cropping season or drained two weeks before harvest when the rice plant is at physiological maturity. The soil condition under a continuous flooding system is anaerobic and the degree of anaerobicity depends on the level of water and oxygen availability [1]. Paddy fields account for about 40% of global irrigation [2] and it uses 2 to 3 times the volume of water required by other cereals such as wheat and maize to produce 1 kg of rice grains [3]. More than half of the water needed for irrigation in Asia is utilized in rice fields; however, most of this water is lost through unproductive water outflows such as evaporation, lateral seepage, deep percolation, and runoff. Apart from its excessive loss of irrigation water, the continuous flooding system is a major source of greenhouse gases such as methane and carbon dioxide thereby contributing negatively to the environment.

As a result of the decline in freshwater, more water-saving irrigation practices such as alternative wetting and drying (AWD), System of rice intensification (SRI), Ground cover production system (GCRPS), Drip irrigation with film mulch (DIP) had been introduced.

2.2 Furrow irrigation

This involves supplying water to the field along the furrow. The furrows are usually small parallel channels that serve as reservoirs of water on the field. The water gets to the plant root through lateral seepage.

The gravity-driven irrigation method requires minimal capital to construct and the energy required for it to work is obtained from free-flowing gravity. The system is easily controlled and does not require high technical know-how. Surface irrigation can be used on sloppy land. However, the irrigation method can affect plant growth and development due to the reduction in plant respiration caused by flooding. It could also increase the loss of water through deep percolation, runoff, infiltration, and evaporation.

3. Pressure-driven irrigation

The increase in global population resulting in rapid urbanization and industrialization have intensified competition for available water resources resulting in the decrease of fresh water available for crop production. Freshwater resources are becoming increasingly scarce and droughts are becoming more common as a result of climate change. Despite moderate rainfall in some regions of the world, over 50% of irrigation demands for crop production are met by pumping from underground aquifers, thereby depleting aquifers at an alarming rate. Therefore achieving food security requires high yields with efficient use of water resources [4]. Water-saving irrigation techniques that involve the use of pressure rather than gravity have been developed to help cope with water deficits and ensure maximum food production per unit drop of water.

A pressurized irrigation system involves the supply of water with the effort of pressure. This system is designed to achieve higher efficiency than the conventional method. The techniques help in quantifying the exact amount of water or nutrient to be supplied at a particular point in time. The choice of a pressurized irrigation system depends on the knowledge of the plant type, soil type, landscape characteristics, required flow rate, operating pressure, and cost. Examples of pressure-driven irrigation system are drip irrigation and sprinkler irrigation.

3.1 Drip irrigation system

A drip irrigation is an efficient irrigation system used for row cropping. In this system, water is directly supplied to the soil surrounding the root region with the of the drip tubes laid on the soil surface (surface drip) or that are buried few centimeters below the ground level (subsurface) (Figure 2). The advantages and efficiency of drip irrigation has increase it acceptance and use by agriculturists around the globe, most especially in the arid and semi-arid regions where there is limited freshwater availability. The precise application of water to the root region of crop without wetting the entire farm plots makes drip irrigation an efficient water-saving technique compared with others. In a drip irrigation system, only a fraction (between 15% and 60%) of the soil surface is wet [5]. The drop by drop sequence of watering reduces surface runoff and percolation; hence, providing better disease management and salinity control [6]. Other benefits of drip irrigation include improved crop quality, efficient fertilizer and other chemical usages, limited weed growth, and improved agronomic practices [7].

Figure 2.

Drip irrigation set up: surface drip irrigation (A) and subsurface drip irrigation system (B).

In a drip irrigation system, emitter spacing is necessary to ensure precise delivery of irrigation water. This largely depends on the planting distance or vice versa. The effectiveness and efficiency of a drip emitter is an important factor that affects water distribution and the performance of a drip irrigation system. The rate of water delivery by emitters varies and their use is based on the soil types and the water-use efficiency of the crop. Emitter clogging is mostly related to the quality of irrigation water. The turbidity of water as a result of physical (sand particles), biological (bacteria), and chemical (inorganic fertilizer, salts) composition results in emitter clogging. The compounds gradually settle around the water passage until the clusters could not allow further passage of water. Clogging affects the productivity of the crops around the affected emitters and in turn reduces yield outcome. However, to prevent emitter clogging, water could be treated and made less turbid before application. The combination of strategies, such as installation of a filtration system, the use of sedimentation tank and tube settlers, frequent flushing of the irrigation system, and chlorination of the irrigation system, could mitigate emitter clogging.

3.1.1 Fertigation and its effect on crop production

Fertigation is the synchronous supply of nutrients or soluble fertilizer and water to the soil through drip irrigation system (Figure 3). The introduction of fertigation to crop production proffers a solution to the problem of flooding and overfertilization. Water and liquid fertilizer are harmoniously applied to the rhizosphere which makes nutrients to be readily available for plant uptake. Fertigation results in increased crop yield and more efficient fertilizer usage [8]. Apart from increasing crop yield, fertigation reduces nutrient losses to the environment. Plants easily absorb soluble fertilizer thereby reducing nitrogen losses as nitrous oxide to the atmosphere. A well-designed fertigation system takes into consideration the appropriate rate of fertilizer and water, duration and frequency of supply to improve water, and nutrient uptake of the crop while at the same time reducing nutrient loss via leaching [9]. An appropriate liquid fertilizer applied through fertigation reduces leaf burn, stem scorching, and root death as mostly observed in the direct application of solid inorganic fertilizer close to the root zone of crops. Furthermore, fertigation reduces disease and pest infestation on crops, attributable to dryness of the plant shoot thereby creating a non-conducive environment for pathogens. The system was created to maximize the use of available water and mineral resources; thus, preventing runoff as it is not affected by wind.

Figure 3.

Schematic illustration of fertigation system.

To improve crop production through fertigation, the application of fertilizer should be done optimally to reduce acidification of the soil, and environmental degradation [10]. However, in case of overfertilization with the use of fertigation, continuous and frequent application of water regime should follow to reduce fertilizer concentration at the root region. Previous reports have documented that the use of fertigation increased both nutrient-use efficiency and water-use efficiency of crop. Nutrient use efficiency increased by 25%, and nitrogen and potassium application reduced by 20% as compared to the use of solid inorganic fertilizer [11]. Also, Ashrafi et al. [12] reported that the absorption rate of solid inorganic fertilizer was estimated to be 10–40%; whereas, the absorption rate of similar concentration on fertigated field was estimated to be 90%. Cotton yield increased by 50% on fertigated plots when compared to cotton supplied with surface irrigation with direct fertilizer application [13]. According to Hebbar et al. [14], drip fertigation enhanced tomato yield by 20–30% as compared to furrow irrigated tomatoes. The yield of Chili was also reported to increase by 52% and saved 40% and 50% of water and nitrogen, respectively through fertigation compared with a check-basin irrigation treatment [15]. Irrigation and nutrient management are the most effective methods for increasing agricultural output [16], and both management can be accomplished by fertigation. However, for successful use of fertigation, knowledge of soil fertility and crop nutrient uptake requirement is necessary.

Advantages of drip irrigation

• Despite its low operating cost as compared with the sprinkler, it is less affected by the speed of the wind.

• It increases the yield due to the efficient use of water and nutrients.

• It helps reduce the cost of weeding and herbicide use, especially when combined with film mulch.

• It is suitable to use in difficult topography.

• It helps to reduce environmental contamination and soil compaction when mineral nutrients are supplied through fertigation.

• In this system, there is little water contact with leaves thereby reducing the risk of plant diseases.

Disadvantages of drip irrigation

• The major disadvantage of a drip irrigation system is the initial installation cost.

• The cost of maintaining drip irrigation pipes might be a challenge to low-income farmers.

• It could be easily damaged by farm equipment, sunlight, rodents, wildlife, etc.

• Fertigation i.e. using the drip irrigation system for nutrient and fertilizer application may bring about the corrosiveness of the system and clogging of emitters.

• Drip irrigation needs to be replaced more frequently than other systems.

3.2 Sprinkler irrigation system

Sprinkler irrigation involves watering plants through a process that imitates natural rainfall. Water is sprinkled into the air through a series of pipes to form droplets before landing over leaves and areas within reach. The water is sprayed through a high-pressure sprinkler or guns. Though, sprinkler irrigation can be used on different land slopes; it is mostly used on flat ground such as lawns, golf courses, crops, landscapes, and flat terrains. There are different types of sprinkler irrigation systems, these include centre pivot system, rain gun system, side roll system, perforated pipe system and rotating head system (Figure 4). Each system is made up of the following components: pump unit, mainline, laterals, and sprinklers. The pump unit takes water from the source while the laterals distribute water from the pump unit to the sprinklers. To ensure efficient delivery of water, several sprinklers must be operated close together, ensuring an overlap of distribution patterns, since the heaviest water application is close to the sprinkler.

Figure 4.

Types of sprinkler irrigation system: Centre pivot system (A), rain gun system (B), side roll system (C), perforated pipe system (D) rotating head system (E).

In a central pivot system, the machine moves in the shape of a circle, and water is sprayed on the crops beneath the circle. A rain gun system necessitates the use of a high-pressure machine that shoots water into the sky and dropped it on the farm in the form of rain. Side roll systems are made up of pipes attached to the middle of a wheel, which is perforated to drop water on the crops below as the wheel rolls across the field. In a perforated drain pipe system, a pipe is perforated to allow water to drain out of it; whereas, a rotating head system makes use of a pipe with spraying head nozzles to water the field. The application rates of sprinklers differ depending on their nozzle size, spray radii, and operating pressure.

Sprinkler irrigation is adaptable to most soil types but it is preferable for sandy soil with low water holding capacity. The water droplets wet both the soil and the crops and are accessible through uptake by the root and foliar penetration. However, sediment-free water is required to avoid blockage of the nozzle.

Advantages of sprinkler irrigation

• This system allows efficient use of water and reduces extra labour required for fertilizer, pesticide, and herbicides application.

• It is more efficient in irrigating plants with higher concentration per unit area of land such as cereals and vegetables.

• It is more effective and efficient for shallow-rooted plants, it is the only form of irrigation that could supply water to less than 1inch depth [17].

• It can last longer than drip irrigation.

• Applicable for agricultural, landscape, and nursery irrigation.

Disadvantages of sprinkler irrigation

• Initial cost of setting it up is high.

• It requires more pressure than drip irrigation, which increases the cost of energy to be used.

• Due to its complex structure, it requires high operating costs.

• Uneven distribution of water is possible due to the ability of wind to control the movement of water.

• Foliar application of water and nutrient could have a detrimental effect on leaves (leaf rot, senescence, and leaf burn) and fruit (fruit rot)

• It could bring about the inefficient delivery of water to understorey crops

• Rate of water evaporation is high in a sprinkler irrigation system.

• It has potential for runoff and erosion compared to drip irrigation.

4. Designing irrigation system

An irrigation design system is a way of determining the efficiency and effectiveness of water use, which involves management that affects the performance, yield, and quality of crops. One of the reasons for an irrigation system is the common phenomena of extreme weather events (e.g., floods and droughts). Recently, advancements in irrigation technologies are increasing. The use of robotics, smart controllers and remote sensing, and soil moisture sensors are gradually integrated into irrigation management [18]. However, the effectiveness of these technologies depends on the design of the irrigation system.

The quality of agricultural products could be improved by adopting this high-pressurized irrigation system, as the supply of water to crops is through piping. Designing effective irrigation systems and equipment will not only save money but will also conserve water, and results in improved agricultural production. The factors to be considered when designing irrigation systems and scheduling irrigation include:

4.1 Water source

The source of water is a determining factor in designing an efficient irrigation system. There are three main sources of water which include, groundwater, surface water and rainwater. Ground water is found under rocks, for example, spring water. Surface water includes water found on the surface of the earth examples are ocean, river, streams and lakes. Furthermore, rainwater from the atmosphere could be collected and used for irrigation. Depending on geographical location, the source and quantity of water for irrigation could differ which in turn could determine the type of irrigation system to be adopted. Also, the quality of available water needs to be considered.

4.2 Field characteristics

Field characteristics such as field size, topography, and soil types are determining factors in the choice of irrigation system, its design, crop type, and planting pattern.

• Field size: The bigger the field, the greater the number of crops that it will contain. Field size will determine the number and size of pumps that will sufficiently irrigate the farm. When designing an irrigation system, the field size will also predetermine the most appropriate source of water that could be effective. Moreover, the pressure for the water to travel to the desired destination will be based on the field size.

• Land topography: Land slope refers to the elevation of land over a specific distance. The flow of water depends on the topography of the land. Water flows from a high elevations to a lower elevations. There is a possibility of flooding at low elevation while there could be insufficient water availability at high elevation. Flat terrain land will allow even distribution of water; however, appropriate irrigation techniques will be required for a contoured or sloppy land.

• Soil properties: The water retention capacity of the soil is determined by its properties which includes structure, texture and organic content. Knowledge about the soil property will give agriculturist an edge in decision making. The soil properties will impact how well plant roots absorb nutrients from it. Nutrient mobility is faster in sandy soil due to its low water holding capacity, whereas it is slower in clay soil due to its high water holding capacity. With a limited water holding capacity, nutrients in the soil leak out, making nutrition uptake by the plant’s roots difficult. Planning of irrigation system requires the knowledge of soil properties for optimum yield.

• Plant type: Plants require different irrigation systems, water application rates and application schedules. Some plants’ are susceptible to insects and pests attack, and disease infestation when their foliar organs are exposed to excessive water or moist condition. Such plants are preferably irrigated through drip irrigation with plastic-film mulch; whereas, crops with high foliar tolerance to water or that require their leaves to be wet should be irrigated with a sprinkler. The duration of life of plants also determines their water requirement, for example, annual crops require less water than perennial plants [19]. The evapotranspiration rate of plants varies, and this influences irrigation scheduling. Plants with high evapotranspiration rates require more frequent irrigation than plants with low evapotranspiration rates. Furthermore, the market value of a crop could influence the introduction of an irrigation system to sustain its production.

5. Improving irrigation system

Irrigation system improvement must take into account agricultural output as well as saving water. The introduction of new crops to an irrigated farm requires technicalities and acquaintance with the crop to the farming system. In the present day, artificial intelligence is an example of cutting-edge technological innovations in irrigation systems. A Photovoltaic (PV) irrigation system is an example of renewable energy resources for improving irrigation systems. The effective management of water for various irrigation uses on a farm depends on the architectural structure of the farm and the mode of operation of the farm operators. Therefore, the system of agriculture may vary from one country to the other. Hence, the need for government to coordinate a sustainable irrigation system in agriculture that suits their Nation [20]. The characterization of the improvement of irrigation systems is a deliberate issue and needs a wealth of knowledge from the technical programming aspect. The deprivation of farmers’ provisional assets may lead to the failure of policy made by government parastatals. This may also result in low farmer turnout in a country or state.

There are factors toward implementing a particular irrigation system and crop cultivation in particular [21]. The integrating components include the irrigation pipe, water pump/tank, valve, emitters, and pressure gauge regulator for a typical drip irrigation system [21]. The capital for implementing the newly adopted irrigation system, the human resources in the coordination, the management of infrastructure and water supply, and the strategy in operating the resources for good crop production are all important to be considered. In summary, the improvement of the agricultural system including the irrigation system needs deliberate policy by government and immense contributions from the scientific community [22].

6. Irrigation scheduling

There are variations in water requirements by plants at different growth stages; hence a need for irrigation scheduling that could supply optimum water required by plants at the appropriate time. Irrigation scheduling considers when and how much water should be applied to plants [23, 24]. These could be predetermined by monitoring the soil water status and the crop water requirements. Soil moisture-based, evaporation-based, and plant-based measurements are the most common methods for scheduling irrigation to aid effective use of water and promote crop productivity.

Soil moisture content can be used to determine an irrigation schedule. The moisture content of the soil is measured with the aid of instruments, these include FDR soil moisture meter (DIK-321A, Daiki Rika Kogyo Co. Ltd., Kounosu, Japan) [25, 26] and when soil moisture goes below a critical level, irrigation commences. The soil moisture-based irrigation schedule takes into consideration the type of soil and its composition to determine the availability of water in the soil. Sandy, loam, and clay have a low, medium, and high availability of water, respectively.

The evapotranspiration schedule takes into consideration soil evaporation and plants transpiration rates. The amount of water required by a plant is determined by balancing the amount of water input into the soil and the amount of water loss. Evapotranspiration data allow us to better understand when to irrigate an actively growing plant.

Also, the plant observation method could be used to determine the irrigation schedule. This method takes into consideration the changes in plant characteristics to determine when to irrigate the plant. There are common morphological symptoms of plants under stress or low water deficit. These visible changes including chlorosis, dried leaves, curling of leaves, and stunted growth were used to assess the timing of irrigation. To determine chlorosis and water stress for irrigation scheduling, a chlorophyll meter (SPAD 502 PLUS, Minolta corporation, Ltd., Japan) and a chlorophyll fluorometer (PAM-2000, Walz Co., Ltd., Effeltrich, Germany) [25] are used.

7. Mulching and its impact on crop production

Mulching is a strategy for enhancing soil conditions that involve covering the soil surface with various materials. It involves covering the soil around the plants’ root zone to protect the roots from an adverse effect of the micro-climate. Mulching has become a popular agricultural practice not just for its immediate economic benefits, such as improved yields, earlier harvests, better fruit quality, and less water usage, but also for its increased soil microbial performance. Mulching creates an environment for the plant to perform at its best as it improves soil temperature, conserves soil moisture, reduces weed pressure and certain insect pests, and makes more efficient use of soil nutrients, among other benefits [27]. The use of mulch reduces the impact of raindrops on the soil surface [28, 29]; thereby, improving the hydrothermal regime of the soil and soil physical properties such as texture, porosity, and infiltration rate.

7.1 Types of mulching

The mulching materials can either be organic or synthetic (Figure 5).

• Organic mulches: These are mulches that can be easily degraded. They are usually available on the farm. The gradual decomposition of the organic mulches increases organic matter and soil fertility (Figure 5A). They host and nurture various beneficial soil organisms such as bacteria, fungi, insects, and worms and their remains in the soil do not create post utilization disposal problems. For example, leaves, paddy straw, grasses, sawdust, sugarcane trash, etc.

• Paddy straw: It has a unique property of not absorbing water and makes water available to plants. Among all the organic mulches, paddy straw has the longest life span. It also serves as a nutrient reservoir and gradually releases them into the soil.

• Sawdust: It is a small granular chip wood that is obtained as the finished product in the sawmills. Easy to apply and inexpensive with high C/N ratio. It retains moisture for longer periods.

• Sugarcane trash: It is the residue gotten from sugar cane after the removal of its juice. Helps conserve moisture and reduces weed growth and should be avoided in an area where there is an incidence of termites.

• Synthetic mulches: These are mulches that cannot be easily degraded (Figure 5B). They synthesized materials that need prior work before using in the field. They are referred to as non-biodegradable as a result of the natural decomposition of organic mulches. They are available in different colors and thicknesses. Much expensive when compared to organic mulches and should be disposed of at the end of the growing season, for example, plastic films

• White plastic mulch: It is good for establishing crops under hot summer conditions and has little effect on soil temperature. It repels some insects and reflects more light on the plant as compared to black mulch.

• Black plastic mulch: It is the most predominant colored mulch and acts as an opaque black body absorber and radiator. It does not allow sunlight to reach the soil; therefore, it suppresses the growth of the weed. It helps to increase soil temperature and improves mineralization and nutrient absorption. It encourages plant growth through the warming of the soil during the winter season.

• Transparent plastic mulch: It is also known as clear plastic mulch. It absorbs little solar radiation with a transmission of 85% - 95%. It raises soil temperature drastically and affects the plant’s growth adversely.

• Degradable plastic mulch: This can either be biodegradable or photo-degradable. It can be degraded by microorganisms or by sunlight.

• Biodegradable plastic mulch: It is made from plant starches such as corn, wheat, and potatoes which can be broken down by microbes. It can be easily plowed into the ground after harvest.

• Photo degradable plastic mulch: It is formulated to break down after a certain period of exposure to sunlight. It has similar qualities to black or clear plastic film. Examples are plastigone and biolane.

Figure 5.

Types of mulch: Organic mulch, for example, rice straw (A) and plastic-film mulch (B).

7.2 Benefits of mulching

7.2.1 Conservation of soil moisture

Several abiotic variables could be responsible for the loss of moisture from the soil. These variables include high winds, elevated temperatures, harsh climatic conditions, etc. Mulching helps to reduce weed infestation and water loss through evaporation. Straw mulch has been shown to minimize evaporation by up to 35%. However, mulching reduces direct soil water evaporation, making more water available for transpiration. This way of water conservation helps the plants to maintain water balance, especially in regions with little precipitation per annum. Also, mulching reduces erosion and nutrient loss by protecting the soil surface.

7.2.2 Minimize soil compaction and erosion

Compaction caused by heavy equipment or machinery is becoming a serious problem on many agricultural lands [30]. The addition of organic mulch materials can help to ease the problem of compaction. These materials prevent compaction due to heavy implements or machinery and from wind and water erosion. It can also reduce the compaction of soil, which can negatively affect the roots of crops, thereby reducing their growth and development. Some grasses and legumes have been used as organic mulch, which serves as the best example of living mulch on the slopes and reduces soil erosion by aggregating the soil particles by binding them into a complex unit.

7.2.3 Regulation of soil temperature

Mulching helps to maintain soil temperature stability, which is beneficial to crop growth and development. Studies have shown that mulch can keep the soil cool during extremely hot weather as well as during normal or warm temperatures. Extreme temperatures have a negative impact on newly emerging plant roots, limiting nutrition and water intake. Plants may be stressed as a result of the extreme temperature conditions under which they grow, and newly established roots may be unable to absorb the proper amount of water and essential plant nutrients [30]. Various types of mulch have different effects on soil temperature. Some mulches increase the soil temperature as compared to bare soil due to the absorption of solar radiation. Moreover, it has been observed that plastic-film mulch and organic mulch materials are better at maintaining a favorable soil temperature compared to other mulch materials.

7.2.4 Reduces infiltration rate

Organic mulch helps to retain water at the soil surface allowing water to slowly penetrates thereby minimizes surface runoff [31]. As reported by Abu-Awwad [32], covering the soil surface reduced the amount of irrigation water required by pepper and onion crops by 14–29% and 70%, respectively.

7.2.5 Reduced fertilizer leaching

Fertilizer loss due to leaching is reduced as excessive rainfall is drained around the root zone, especially in sandy soil. Also, the use of organic mulch increases soil organic carbon which improves the water and nutrient holding capacity of the soil. Mulching with coconut fronds increased leaf N, P, and K content in chili [33]. Findings have shown faster plant growth, early fruiting, reduced P, and increased N concentration in leaves and fruits of crops when mulch is used.

7.2.6 Reduces weed infestation

Mulching reduces the germination and nourishment of many weeds by providing a physical barrier between the soil and the atmosphere. The mulching operation promotes the reduction of weed seed germination and weed growth and keeps weeds under control. Weed seed germination can be prevented or physically suppressed by covering or mulching the soil surface. Weed control can be achieved with materials like rice and wheat straws. Covering the soil surface can prevent weed seed germination or physically suppress seedling emergence. Organic mulch such as rice straw and sugarcane bark can provide effective weed control.

7.2.7 Organic matter improvement

Mulches decompose and restore organic matter and plant nutrients to the soil. Improving the physicochemical and biological properties of the soil which in turn increases crop productivity. Organic mulches do not only help to maintain soil moisture, but they also greatly enhance soil nutrients by adding organic matter. Lal et al. [34] reported a decrease in bulk density under straw mulch (1.42 g cm-3) compared to bare soil (1.50 g cm-3). Khurshid et al. [31] concluded that organic matter was significantly higher when more mulch was applied.

7.2.8 Reduces harvesting period

Vegetables such as cucumbers, muskmelons, watermelons, eggplants, and peppers usually respond well to mulching in terms of early maturity and higher yields. In comparison to control, organic mulches cause earlier blooming, resulting in fewer days between fruit set and harvest in tomato crops [35]. Polyethylene used as mulch reduced the growth season and increased the earliness and productivity of various vegetable crops [36, 37].

7.2.9 Improves quality and yield

Mulch keeps fruits clean from touching the ground and reduces soil rot, fruit cracking, and blossom end rot in many circumstances. Fruits are smoother and have fewer scars. Plastic mulch when properly laid prevents dirt from splashing onto the plants during rainfall, reducing grading time. Moreover, straw mulch can also improve the yield and quality of early potatoes, cabbage, and other vegetables.

7.2.10 Reduction of diseases

Mulch can reduce the force of irrigation water or the beating motion of raindrops, which can convey disease spores. These spores attach themselves to vulnerable plants’ leaves and branches. Mulches provide food for a variety of beneficial soil organisms that compete with entering harmful spores or emit compounds that suppress diseases. They minimize the possibilities of illness occurring in plants. Many soil bacteria are inhibited by organic mulches, which compete with or digest pathogenic organisms through a variety of enzymatic processes. Mulches play a crucial role in integrated pest management (IPM).

7.2.11 Remediation of heavy metals

Heavy metals are harmful to the health of both animals and humans. Mulches are an excellent source for removing heavy metals from soils. Eucalyptus leaves are commonly used to remove heavy metals from soil solutions [38]. In forest environments, woodchips and compost can form complexes with copper metal, converting them to a non-toxic form for crop plant growth [39].

7.3. Negative impacts of mulching on crop production

7.3.1 Competition for resources

Mulches most especially organic compete with the main crop for resources such as water, nutrients, oxygen, carbon dioxide, and space. The inter and intra-specific rivalry for the resources could be fierce. Both types of competition are harmful to the growth and development of the main crop.

7.3.2 Allelopathic effects

Allelopathy is the term used to describe the limitation of seed germination and plant growth caused by the release of allelochemicals by some plants or organic mulches. Allelochemicals inhibit weeds in crop plants; however, previous studies have shown that when plants like eucalyptus, acacia, and pine were mulched, they lowered or completely suppressed the growth of numerous weed species, demonstrating their allelopathic actions. Narrow-leaved plants, such as grasses, are not as badly damaged as broad-leaved plants or dicot species [40].

7.3.3 Weed infestation

The partially decomposed organic mulch materials could act as carriers of various weed seeds. Incorporation of mulch to a deeper depth could help to mitigate the problem of weed seed because at a deep depth the growth of weeds is suppressed before getting to the surface. Organic mulch can inhibit the growth of weeds by depleting air and resources necessary for their growth, thereby promoting healthy plants and soil. Previous study has shown that weed suppression is directly related to the depth of mulch [30]. Organic mulches that are applied at a higher depth can reduce weed species as compared to those applied at shallow depths.

7.3.4 Nitrogen insufficiency

Organic mulching results in nitrogen deficit in the soil. They require nitrogen to decompose since they contain high structural carbohydrates such as lignin, cellulose, and hemicellulose and reduced non-structural carbohydrates. As a result, they compete with the crop for nitrogen, lowering their C/N ratio. Though the accumulated nitrogen will be released to the soil after decomposition, the crop may suffered nitrogen deficiency at critical stages of plant growth, resulting in chlorosis.

8. Water management for sustainable integrated pest management

Integrated pest management is the method of controlling pests, especially insect pests that invade farmland [41]. Crop production on farmland becomes more vulnerable to pest invasion if it is not closely monitored, which can result in crop damage and significant financial loss for farmers. The objectives of integrated pest management can be classified into three categories.

• Sustainable ecosystem maintenance and the reduction of pesticide negative impacts.

• Cost-effective farm production.

• Maintaining and putting human and animal health in check.

However, the role of farmers and stakeholders in the management of crop production and agricultural farmland is imperative. The success of the control tactics must be measured using indicators based on monitoring of harmful and beneficial organisms, pesticide use, and their impact on the environment [41]. Greenhouse gas emissions as a result of pesticides and fertilizer application on agricultural land contribute largely to global warming potential [1]. The connection between measuring CO2 gas fluxes emission and pesticides applied through irrigation is critical in examining the impact of the chemical–water ratio applied to the soil rhizosphere and mineral nutrients available to the crop [42, 43].

Irrigation is an essential agricultural practice for food, pasture, and fiber production in semiarid and arid areas [42]. Fertigation allows flexibility in the application timing when injections can be made virtually any time during the season from the point of the seedling establishment until harvest. The intensive use of water in the irrigation system is inherent in the cumulative effect of the modeling concept of the irrigation system. The inclusive role of the model and pesticide application is important in an integrated pest management system. However, the use of water in a non-essential way may lead to a high pest in-breeding rate. Hence, there is a need to plan the amount of water pumped into the irrigation system and also calculate the relative drip chemigation used [42].

To ensure a sustainable integrated pest control system, the connecting pipes and the osmothermal capacity of the pipe used for surface irrigation must be regularly examined for an effective irrigation system. The internet of things (IoT) and big data collection are new advancements in the application of addressing irrigation system defects while also monitoring integrated pest management activities [42, 44]. Relative data used in IoT is the collection of previous crop performance and farm production activities. This will enable the farmer to predict the future production of the crop. A large amount of data must be collected to amuse the net profit on crop production.

The cost of controlling pests on farmland must be reduced and be effective to make it a success. Combining the relative evaluation of the integrated pest management innovation system and the new event on irrigation system on crop output is not excessively expensive as compared to the success it will bring to farmland. Pesticide application through fertigation is a common example of combining insect pest management with a drip irrigation system. As a result, there exist methods for managing crop water availability as well as applying chemical pesticides and liquid fertilizer efficiently for agricultural production management. Furthermore, the building of irrigation system components that suit the topography of the soil and planting pattern is critical for successful crop production.

Though there is no specific way of designing an irrigation system for sustainable integrated pest management, what matters is making sure it is designed in a way that will reduce water usage without hampering the efficacy of the pesticide and also protecting the environment. The use of chemigation systems is an advancement that could help in achieving the goals for integrated pest management.