GSR did an installation on a Macadamia plantation. Contact David for access to the demo site and see for yourself the value of irrigation scheduling. Save water and electricity whilst increasing crop quality.
It's a win-win situation!
South Africa is classified as a semi-arid country with 465mm of average annual rainfall. This is below the global average estimated at 860mm per annum. Roughly 20% of South Africa receives less than 200mm and 47% receives less than 400mm yearly.
The figure below indicates the rainfall distribution.
Figure 1: South Africa’s Mean Annual Precipitation (MAP) (Source: Schulze 2011)
Water use for irrigation agriculture takes place on an estimated 1.1% of South Africa’s total land surface area, often in low rainfall areas where supplementary irrigation needs are very high or total irrigation is practiced. A relatively inefficient mode of irrigation was found to be in use in most cases.
In 2000 eleven of the 19 catchments listed in the table below indicated a negative water balance. In South Africa’s major catchments local water demands exceed the reliable local yields.
Table 1: Reconciliation of water availability and requirements for 2000 (million m3/annum) (Source: DWAF 2000) (* refers to the amount that can be reliably provided 98 years out of 100, with ecological reserve requirements already subtracted)
The figure below indicated South Africa’s water usage by sector. Irrigation comprises nearly 60% of total water consumption. Irrigation water usage in agriculture was 6907 million m³ in 2002. This was 87% of the total water allocation for irrigation purposes (7920 million m³) as reported by the Department of Water Affairs and Forestry.
Figure 2: SA water use by sector. (Data Source: DWAF 2000)
Compaction and water saturation of soils are the main barriers to soil oxygen transport, water being a more effective barrier (Papendick and Runkles, 1965; Moldrup et al., 2000a; Neale et al., 2000). The diffusion of gases in water is slower than their diffusion in air by a factor of 10⁴ (Call, 1957; Moldrup et al., 2000a; 2004; Thorbjorn et al., 2008).
Suzanne DeJohn (2017) summarizes this problem adequately "Soil that’s too wet can also cause wilting, as excess water pushes air out of the soil and suffocates the roots." Plants need oxygen to absorb water and nutrients from the soil. Waterlogged soil essentially "drowns" the root-zone, impeding the biological and chemical processes necessary for healthy plant growth and crop production.
As indicated above, irrigation scheduling reduces waterlogging problems, therefore assisting with soil aeration by minimizing the most significant barrier to soil oxygen transport i.e. too much water.
Farmer's Weekly posed in interesting question with one of their September, 2017 articles. Essentially they asked "How many harvests are left in your soil?" Maria-Helena Semendo, speaking at World Soil Day (2016) stated that the world's topsoil could be gone within 60 years should the current degradation continue. Some of the main causes of soil degradation include chemical-heavy farming methods, deforestation, erosion and global warming.
Professor Raj Patel points to runoff water from farms often contaminated with high volumes of fertilizer and other chemicals as being a culprit. “The story of industrial agriculture is all about externalizing costs and exploiting nature,” Patel states.
South African farmers are already taking the lead by becoming more ecologically accountable, by incorporating green farming practices and turning to sustainable farming methods and water conservation. One of the methods South Africans employ are irrigation scheduling, or the precise control of irrigation.
The question now remains how does irrigation scheduling and sustainable farming form a beneficial symbiotic relationship?
The Journal of Experimental Botany describes irrigation scheduling as "conventionally aimed to achieve an optimum water supply for productivity, with soil water content being maintained close to field capacity. In many ways irrigation scheduling can be regarded as a mature research field which has moved from innovative science into the realms of use, or at most the refinement, of existing practical applications. Nevertheless, in recent years there has been a wide range of proposed novel approaches to irrigation scheduling which have not yet been widely adopted; many of these are based on sensing the plant response to water deficits rather than sensing the soil moisture status directly (Jones, 1990a)."
"Irrigation scheduling is conventionally based either on ‘soil water measurement’, where the soil moisture status (whether in terms of water content or water potential) is measured directly to determine the need for irrigation, or on ‘soil water balance calculations’, where the soil moisture status is estimated by calculation using a water balance approach in which the change in soil moisture (Δθ) over a period is given by the difference between the inputs (irrigation plus precipitation) and the losses (runoff plus drainage plus evapotranspiration). Soil moisture measurement techniques have been the subject of many texts and reviews (Smith and Mullins, 2000; Dane and Topp, 2002)" The former category relying on direct soil moisture measurement is a more reliable method, especially with hourly measurements as current data cancels the need for additional data. Continuous data adapts and reacts to changing weather and other variables that would otherwise make precision irrigation scheduling a guessing game. The Journal of Experimental Botany indicates that the "the water balance approach is not very accurate".
With increasing water restrictions and unpredictable dry-spells irrigation scheduling is fast becoming a crucial tool for sustainable farming. A farmer is able to accurately control their water usage through irrigation scheduling and thereby contribute to sustainable farming practices. Therefore the farmer cannot afford to use inaccurate methods of irrigation scheduling as this would impact on crop yield and soil health.
According to Agriculture and Agricultural Science Procedia "Water is considered as the most critical resource for sustainable agricultural development worldwide. Irrigated areas will increase in forthcoming years, while fresh water supplies will be diverted from agriculture to meet the increasing demand of domestic use and industry. Furthermore, the efficiency of irrigation is very low, since less than 65% of the applied water is actually used by the crops. The sustainable use of irrigation water is a priority for agriculture in arid areas. So, under scarcity conditions and climate change considerable effort has been devoted over time to introduce policies aiming to increase water efficiency based on the assertion that more can be achieved with less water through better management" (Konstantinos Chartzoulakis, 2015).
Precision irrigation scheduling, therefore, would become a critical tool for farmers. Precision engineered equipment (probes, nodes, valve actuators and web-based software) are vital tools of the trade that allows the farmer to essentially "see" in the soil and therefore make informed decisions about watering needs.
Irrigation Scheduling has several advantages. Apart from the obvious decrease in water usage farmers find the following to be true:
Adding #valve #actuation / #automation to irrigation scheduling will further enhance the benefits as #probe data can determine the length of irrigation required and shut of valves in real-time.
The importance of irrigation scheduling is that it enables the farmer to apply the exact amount of water. This increases irrigation efficiency. A critical element is accurate measurement of the volume of water applied or the depth of application. A farmer cannot manage water to maximum efficiency without knowing how much was applied. This is where valve automation becomes critical. As the units are linked on the same software platform real-time, current data can determine the irrigation requirements, thus maximizing the usage of available water.