Drip Irrigation And Fertigation, An Inseparable Duet

The emergence of agriculture represented an important, and possibly the most significant, milestone in the development of human civilization, as it gave rise to the Neolithic Revolution. The availability of water is the most decisive factor for the growing of crops and civilizations evolved along the banks of rivers or in areas with enough rainfall to cover the needs of the first crops. The natural fertility of the soils, water levels of the rivers and use of animal manure made it possible to achieve a sustained, but limited, food production. After a period of 8,000 years, it was only 100 years ago that the Haber Bosch technique made it possible to overcome the production ceiling resulting from the shortage of Nitrogen in the soil. More recently, metallurgy and plastics have contributed to the development of pressurized and drip irrigation techniques, also known as localized irrigation. Wherever it has been possible to meet the demands of climate, water and nutrition (in correlation with the diagnosis of plant diseases and genetic improvement), global agricultural production has increased dramatically over the last 50 years.

The drip or trickle method is used on approximately half of the irrigated land in Spain with a similar proportion in India, China and the United States. This proportion is only surpassed by Israel (>70%). This method represents about 20% in Italy and South Africa and over the last few decades it has expanded worldwide, particularly for horticultural and fruit crops. Following significant research and development, it can now also be used with crops such as olives, vines and almond trees, which had previously been grown on non-irrigated land.

The technological development has been so intense that it has been necessary to review the basic traditional concepts of irrigation. We have sometimes seen the inappropriate use of technology with negative consequences for the environment, yields and costs. It is essential that access to new communication technologies goes hand in hand with a critical view of the global nature of agricultural technology. The harmful effects caused to the groundwater, rivers or lakes, due to the concentration of nutrients inappropriately applied to crops, as well as loss of fertility in agricultural areas, were the result of widespread and commonly accepted procedures.

The information available on the Internet offers information about an enormous range of macro­nutrient requirements. Inevitably, some of these will be incorrect. However, the farmers are attracted to the results potentially achieved from their application since this will lead to increased production and they find it difficult to determine the role played by each factor (location or planting density, adaptation of the varieties, climate variations, texture, schedule, etc.) within the context of the overall results.

Fertigation combines the concepts of irrigation and fertilization. The interaction of water, air and ions in the rhizosphere is extremely important in the case of localized irrigation. In these irrigation systems, the volume of soil explored by plant’s roots is reduced, and despite the very frequent and necessary water applications, the wetted volume varies greatly. If the wetted bulb is minimal, it is even smaller just before irrigation. The cation exchange complex that has assisted farmers for thousands of years is now reduced to a fraction because the plants have less soil available. We have lost a powerful chemical buffer, a reservoir for the surplus and a source of nutrients in times of need.

The time-honoured legacy of agricultural expertise loses its usefulness as change occurs in the environment where it is applied.

The “large quantity” of evaporation and inputs, expressed in cubic meters and kilogrammes per hectare, do not reflect the sheer scope of these changes and their distribution within the wetted bulb. The solution on many occasions was to adopt routines involving too frequent and excessive applications of water and nutrients, guaranteeing their sufficiency and eliminating the surpluses.

The reduction of the wetted bulb that causes the drying of large sections of soil concentrates the ions present, encouraging the formation of insoluble precipitates. The dynamics of precipitation and saline dissolution are not reversible and many of these precipitates will not return to the soil solution: e.g. Phosphorus, Calcium, Magnesium, among others, and they remain out of reach for the plant. At the same time, the pH of the absorbed soil solution will change, depending on these increasing concentrations of the ions. On the other hand, fertigation is essential in the practice of drip irrigation, as it is the only method of adding enough nutrients within the reach of the crop, which can no longer explore an appropriate volume of soil.

Fertigation and drip irrigation form a necessary partner relationship. The technology must be channeled towards ensuring that the water and nutrients are always readily available to the crop, especially at the plant’s key stages of growth where a water deficit would be critical. ‘Readily available’ means that, hydraulically, the soil-water tension is not high and that the soil contains all the elements that the crop will be able to absorb for its growth and metabolic processes.

The use and efficiency of water and nutrients are linked to spatio-temporal continuity. Every litre of water has to be utilized to convey the nutrients, thus obtaining irrigation solutions with minimal salinity, that are more stable in the soil and more readily absorbed, with a lower osmotic potential. Consequently, there will be a higher spatial distribution of the nutrient in the wetted bulb. To achieve this, it is necessary to reduce to the minimum the amount (and duration) of water applied without fertilizer in the pre- and post-irrigation processes and set aside the concept of irrigation without nutrients.

We now known that it is essential for the irrigation to be uniform and consistent. That is why it is useful to know the soil water holding capacity and crop water requirements. In fertilization, these principles are reflected in the need to ensure that the nutrients are thoroughly dissolved in the water at all times. If there is a variation in the flow rates of the irrigation systems and the nutritional requirements of the crops vary throughout their growth cycles, the dosing system must also be able to adapt to these changes.

It is quite normal that, at the time when more irrigation must be applied, the water-nutrient ratio is lower and it is also the case that, when there is more natural rainfall or less transpiration, the plant’s demand for nutrients cannot be immediately satisfied due to the limited level of irrigation if the system is not designed to take these factors into account.

To achieve a good match between irrigation and fertilisation, then precision dosing pumps with a large working range have to be used, which operate at a high level of precision across the whole range. The electronic technology introduced in the manufacture of dosing pumps has made it possible to achieve flow rates in a range of 1:3000, so that, for example, a pump that injects up to 60 litres/hour, can equally inject 20 millilitres/hour at a normal flow rate.

It is clear that this variation in the dosage of the fertilisers and nutrients can also be achieved by dissolving them in a larger quantity of stock solution and injecting it into the main pipeline at a higher flow rate, but this means that larger volumes of stock solution have to be handled leading to higher energy consumption and less control over the solutions employed. On the other hand, more diluted solutions cannot be used in other irrigation sectors with greater requirements or with dosing devices capable of injecting huge amounts of stock solution, which would result in additional financial investment and higher energy costs.

It is obvious that, technology permitting, the precise dosing of highly concentrated stock solutions would be chosen, at a minimal rate, for as long as possible (in as large a volume of water as possible) and proportional to the flow rate available in the pipeline. Therefore, with more efficient agitation systems, capable of obtaining highly concentrated solutions, and precise dosing pumps with low flow rates, the irrigation solution is more uniform, and each drop of water contains the same amount of nutrients. This requires the precise measurement of the flow rate of the irrigation water using high-frequency flowmeters. With a uniform irrigation system, each dripper distributes the same quantities of nutrients and the objective of providing an even crop with a uniform amount of nutrients is achieved.

The acidic nature of fertilizer solutions is also quite common and a good idea. Apart from the advantages they have of removing carbonates from the pipes and drippers, acidic solutions contribute towards the stability of the irrigation solution and the absorption of certain nutrients by the crop. The pH has an influence over the absorption of Phosphorous, Calcium, Magnesium and Iron, among others. Managing the pH, essential in hydroponic farming, has become widespread in the intensive agriculture practices carried out in greenhouses, but its use with field crops, market gardening or fruit tree growing is still limited.

The success will cme by combining the expertise of the farmers with technological tools characterized by easy and intuitive use and available on an everyday basis, such as the elements such as the mobile phone. And it will allow for the application of integrated amounts of water and nutrients; for environmental parameters to be measured in real time; and modifications to be made according to the weather forecasts.

The traceability and analysis of results are essential for establishing the strategy of tomorrow. Fertigation teams must then be able to incorporate information taken from the field into the planning process and determining the actual needs of the crop as well as providing the requested information in a single click, thus facilitating decision-making, the activities of technicians in the field and traceability, while operating with maximum reliability, accuracy and precision.

 

Author
Xavier Martínez Sagarra, Technical Agricultural Engineer at ITC Dosing Pumps