Drought, desertification and management of water resources

Irrigation Planning and Water Management Analysis

Dr Marcello Mastrorilli
Agronomic Research Institute

Today, water represents a fundamental limit for the health and well-being of the population on earth, and the demand for water will likely grow in the future.

In the agricultural sector, the requests for water always become more pressing due to:
  • The increase of the level of agricultural productivity;
  • The effects of global warming of the air caused by the so-called “greenhouse effect”;
  • Deterioration in water quality.

The threat of drought and desertification in the Mediterranean region should be faced in good time, by studying the correct water management. Improving the efficient use of water for irrigation, particularly in the agricultural sector, brings about a notable saving of resources. It will be advantageous for irrigating other areas, in the environment and in other productive sectors.

The efficiency of water for irrigation increases by:
  • Distributing water at the most suitable time for the plant;
  • Suitable cropping choices;
  • Avoiding excesses;
  • Resorting also to anomalous waters.

Agronomic research has acquired the techniques for:
  • Measuring the consumption of water of cultivated plants;
  • Simulating the productive processes through crop models.

With these methodologies, we will extract the indications of the impact on desertification or other possible climatic scenarios on agricultural productivity of a territory.

The main objective of the research is evaluating, in technical terms, the risks derived from:
  • Climatic variations;
  • The reduction of availability of water for irrigation.

Both the irrigation planning on the farm level and the analyses of water management at a district level are based on the evaluation of water balance.

The soil is considered as a tank of water which, following rainfall (according to net runoff), refills with the contribution of the groundwater and the irrigation, and which empties out under draining action and effective evapotranspiration (ET).

After having calculated the ET according to the “Penman-Monteith formula”, we attempt to apply the “agronomic” model, capable of estimating the following at the farm level, through different combinations of “crop-soil-climate”:
  • The irrigation schedule without water limitations;
  • The phenological phases in which water stress is verified in cases of limited irrigation systems;
  • The reduction of productivity when the requirements of the culture not completely satisfied;
  • The irrigated volume adjusted according to the water quality.

At the territorial level, the following will be used to forecast the consumption of water and the functioning of the crop yield :
  • The adopted cropping techniques;
  • The type of soil;
  • The possible climate change (“weather generator”).

Ruscellamento= runoff
Percolazione profonda=deep percolation?
Risalita capillare=capillarity rises
PA (Punto di appassimento)=wilting point
CIC (capacità di campo)=field capacity

The soil is considered as a tank of water which, following rainfall (according to net runoff), refills with the contribution of the groundwater and the irrigation, and which empties out under draining action and effective evapotranspiration (ET). This last parameter is a function of the climatic request (ETP), of the water reserve of the soil (RU) and of the cultivated crops.

In the framework of the project, we will calculate the ET using the “one-step” Penman-Monteith formula. In this way, one avoids “doubling estimations”, that is, first the estimation of the ETP and then that of the ET, by adopting of crop coefficients (kc). The original version of the Penman-Monteith model, rather, permits calculating the effective ET of the crop when we know the values of the resistance of the vegetal cover (rv). This ecophysiological parameter is difficult to determine (varying with the species, the time of day, the phenophase, the water state of the soil) – therefore, the Penman-Monteith equation loses functionality and comes to be applied in some research centres.

The studies conducted at the Agronomic Research Institute on the evapotranspiration processes have shown the existing relationship between rv and the water state of the crops (expressed through the potential to foliate as measured before the dawn, Y). Since this relationship assumes a general validity (but specific for the crop), it was introduced in the Penman-Monteith formula, rendering it largely functional. In the course of the project, a further step towards complete functionality of the formula is entails facing all ecophysiological measures that are difficult to find at the regional level. We intend, therefore, to adapt Y according to available water in the soil (AW) to correct further the Penman-Monteith formula without having it lose its scientific rigour.

Once the problem of determining the ET is overcome, we intend to apply the “agronomic” model, which is capable of estimating the following for every combination of “crop-soil-climate”:
  • The irrigation schedule without water limitation (ETm);
  • The phenological phases in which water stress occurs in the case of systems of limited irrigation;
  • The reduction of yield (r/R) when the demand of the crops not being totally satisfied.

This instrument allows the agricultural operators to use an objective method to decide when to irrigate and how much. In case of anomalous waters, the quantity of irrigation volume will be modified according to the quality of the water. At the district level, however, this instrument allows to predict the consumption of water and the productivity according to the adopted cropping techniques, the type of soil, land, and possible climate changes. The objective of this simulation is the evaluation, in technical terms, of the risks derived from climatic variations and the reduction of the available water for irrigation.

In the first year, we will gather the necessary data to calibrate the ET model, in consideration of the hypotheses on the irrigation requirements of some representative crops of the Mediterranean environment (i.e. maize, wheat, sorghum, beetroot, tomato). The evapotranspiration data will be measured continuously through the “eddy correlation” technique, according to the ET of the crop, while the ETref will be calculated by the weight-measuring lysimeter on a crop in the field. The hydrological state of the plant and the soil will be determined, respectively, with a “pressure chamber” and with the gravimetric method. Further, there will be systematic research to check the quality of the rainwater and of the layers.

In the second year, the ET model will be verified, comparing the output of the model with the measured data of the actual situation for crops in the agricultural farms within the territory.

In the final year, the “agronomic model” will be used at the territorial level to forecast the irrigation requirements after climatic variations, the substitution of agronomic techniques and the changes in productive orientations. In this way, we will concretely evaluate the possible choices of the farmers of a territory, taking into account the crops under irrigation, the physical and agronomic characteristics of the farms, the availability and quality of the water resources, and the characteristics of the implemented irrigation system.

The agriculture issue in southern Italy opens up new interests relating to the environment including the valorization of the richness of the environment and the non-conventional use of water to compensate for the chronic lack of water. Only with adaptation is it possible to analyse the various aspects in a diverse enough panorama, that by interacting contemporaneously determine the variations of the water in the soil in space and time. In the Mediterranean environment, characterized by semi-arid climate, the current models very roughly simulate the water requirements of the crops and, consequently, become useless for irrigation management, especially regarding the need to make the most of limited water resources.

The research-designed “agronomic" model uses a group of indicators that are easy to find, relating to the climatic conditions, the water state of the soil, phenological stages of the crops, and the availability of the water resources (in quality and quantity) to plan the irrigation and analyse water management in a territory. Further, this proposed method is able to face different climatic and agronomic scenarios. For every condition, the method will re-construct the simulated irrigation scheduling according to the crop, soil type, and the productivity and the percentage to satisfy the water requirements of the crops.

This proposed model rests on a solid theoretical base, requiring input data that is easily found and supplying output that can be quickly verified. These aspects constitute a real advantage in respect of other solutions that require a long and laborious calibration phases.

The ET models have been developed above all as research instruments. Despite this, their use should be disseminated in agricultural practice to suitably choose the irrigation variables. If these calculations, being scientifically corrected, come to then be introduced in more general models of agronomic management, it will be possible to distinguish their technical paths. These paths should better valorize the irrigation water, respect the environment and be economically sound. In the current scientific literature, different ET models are contemplated, but the choice is reduced when one moves to practical applications of the model to the final user. In this case, it is preferable that the model be sufficiently complex to consider the physics of the evapotranspirational process, but this would require a reduced number of variables that are easily and widely available.

The proposed “agronomic” model represents a simple (the data being easily found) and reliable (rigorously scientific) method to determine irrigation consumption and an indispensable guide for farmers and decision-makers who intend to use water in agriculture in an appropriate way. The “operative” phase of the research consists in hypothesizing various agrometeorological scenarios, different availability of water resources, the worsening of water quality, and irrigation strategies that are differentiated in order to then verify the consequences of the crop yield and the consumption of water.

  • Mastrorilli, M., Katerji, N. & Rana, G. 1997a. Productivity of sweet sorghum: a multipurpose crop with great potential for exploitation next century. Proceedings from the First International Sweet Sorghum Conference, FAO”. Li Dajue (ed.), 155-162.
  • Mastrorilli, M. et al. 1997b. Restituzione in atmosfera dell’azoto ammoniacale durante la decomposizione di una “cover crop” leguminosa. Riv. di Agron., 31, 3, 786-791.
  • Mastrorilli, M. 1998a. Gestione sostenibile delle risorse idriche. Bonifica, 47-49.
  • Mastrorilli, M. 1998b. Italy: the Capitanata irrigation scheme - experiences in water sustainability. In Case studies, OCDE Paris, 99-108.
  • Mastrorilli, M. 1998c. L’uso sostenibile dell’acqua in agricoltura. L’Informatore agrario, LIV, 17, 56-57.
  • Mastrorilli, M., Katerji, N., Rana, G., & Ben Nouna, B. 1998a. Daily actual evapotranspiration measured with TDR technique in Mediterranean conditions. Agricultural and Forest Meteorology, 90, ½, 81-89.
  • Mastrorilli et al 1998b. Criteri e prospettive per un’irrigazione sostenibile. Atti del convegno “Agricoltura sostenibile” 53-62.
  • Mastrorilli 1999. Sviluppo di modelli idrologici per ambienti mediterranei. Bollettino SIS, 48, 1, 245-250.


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