**4. Investigations of medium-time period (60 years) in intensive agriculture**

For the medium-time investigations, the consequences of intensive agriculture of the last 60 years have been studied in the irrigated grasslands in Crau's area (hay production with COP label) in southeast of France.

#### **4.1 Materials and methods**

The Crau's area covers up to 600 km2 at the south of Alpilles mountains. A part of the territory is occupied by a natural semiarid steppe, named "coussoul," and, in another part, by irrigated grasslands and orchards. Thanks to Adam de Craponne, a sixteenth-century engineer, a first irrigation canal was built up, and the irrigation network extended until the nineteenth century. The network supports the production of the Crau hay with a protected designation of origin, which is exported all over the world to feed racehorses, the Sisteron lamb, and the Arles Merinos sheep, which are

produced with a label of geographical indication of origin. Irrigated grassland production is regulated by three cuts of hay (i.e., cut 1, cut 2, and cut 3) and sheep grazing in the field during the winter. The gravity irrigation with water of Durance river secures the renewal, up to 70%, of the groundwaters in the aquifer, which supply the water consumption of 280,000 inhabitants and industrial activities of Marseille harbor.

A database concerning hay's mineral content, dry matter, and climate dynamics was statistically analyzed [6].

In addition, the geochemical variations of water composition during its pathway from irrigation channel till the phreatic aquifer were recorded and modeled. For modeling with PHREEQC software [7], we have defined a priori the processes, which can impact water chemistry, such as evaporation, dissolution, precipitation, and exchange with the plant [8].

#### **4.2 Results and discussion**

Nitrogen and phosphorus contents in hay increase from cut 1 to cut 3, whereas the potassium decreases significantly in cut 3. These results are explained by seasonal changes in the floristic composition of the hay [9]. But globally the total inorganic content in Crau hay increases over time from cut 1 to cut 3, and this order has remained constant since 1960 (**Figure 5**).

Statistically, these results show a steady state of the production, which has been maintained, both in quantity and quality despite an average temperature increase of 1.9°C since 1960 [10].

For each chemical element measured in the waters, a model of fluxes is built up [6]. Activities and saturation indexes (*SI* = log Q − log K) were computed by using PHREEQC [7], using phreeqc.dat database: activity coefficients were computed with Debye-Hückel extended law, as ionic strength is small enough (*ca.* 0.01 M). The reaction of reduction of nitrate into ammonium was removed from the database as it is biologically mediated, and N(III) and N(V) were considered as distinct elements separated by a kinetic barrier.

On **Figure 6a** models for calcium are presented. At each step, where chemistry of water changes, the soil solution is computed. The time step is 2–3 months corresponding to the duration of hay growth for one cut. Thus, between solution S1 and S2, the evaporation of the water induced a loss of water and a concentration of the elements. Then, from S2 to S3, the pCO2 (partial pressure of CO2) of the soil, which is 30–100 times larger than in the outer atmosphere, results in acidification of solution and calcite dissolution. From S3 to S4, the model

**77**

**Figure 6.**

*Geochemical Methods to Assess Agriculture Sustainability*

simulated the fertilizer impact on the soil solution. Inorganic fertilizers (P, K) consist of gypsum CaSO4.2H2O, calcium dihydrogenphosphate Ca(H2PO4).2H2O, arcanite K2SO4, and sylvite KCl. The last three minerals were introduced in the database, with their thermodynamic properties [7C]. Dissolution of fertilizers was simulated by PHREEQC as the dissolution of a mixture of the above minerals. From S4 to S5, the model simulated the element uptake by plants. P absorption by plants was simulated as the removal of calcium phosphate from the solution, S absorption by plants as the removal of gypsum, and calcium being absorbed in excess to the sum of P and S, the remaining Ca absorption was simulated as a CaO removal from the solution; Na, K, and Mg absorption by plants were simulated respectively as the removal of Na2O, K2O, and MgO from the solution. Removal of elements by plant is computed by PHREEQC as a dissolution with negative coefficients, in the same way as evaporation is computed with a negative coefficient for water. To avoid transient negative concentrations, fertilizer dissolution was simulated before absorption by plants. In point S5, the

*(a) The pathway of calculation of fluxes of Ca during soil solution changes from surface irrigation water to groundwater; (b) for the 4 years of monitoring of water in Crau's area, comparison between measured and* 

*computed values of Na, Ca, Mg, C, K, S, and Cl for each cut (from [6]).*

soil solution is reequilibrated with the minerals of the aquifer.

The fluxes have been computed for the three cuts per year during 4 years of monitoring the water quality both in irrigation network and in groundwater (**Figure 6b**). All simulations are computed at the average temperature of

*DOI: http://dx.doi.org/10.5772/intechopen.85336*

#### **Figure 5.**

*Nitrogen and total inorganic element contents in hay as function of the cut (from [9]). The mineral content of the hay is defined, per unit of dry matter expressed in percentage, by the sum of the content of the following elements: phosphorus, potassium, calcium, magnesium, sodium, iron, manganese, copper, and zinc.*

*Geochemical Methods to Assess Agriculture Sustainability DOI: http://dx.doi.org/10.5772/intechopen.85336*

#### **Figure 6.**

*Applied Geochemistry with Case Studies on Geological Formations, Exploration Techniques…*

was statistically analyzed [6].

and exchange with the plant [8].

has remained constant since 1960 (**Figure 5**).

elements separated by a kinetic barrier.

**4.2 Results and discussion**

1.9°C since 1960 [10].

produced with a label of geographical indication of origin. Irrigated grassland production is regulated by three cuts of hay (i.e., cut 1, cut 2, and cut 3) and sheep grazing in the field during the winter. The gravity irrigation with water of Durance river secures the renewal, up to 70%, of the groundwaters in the aquifer, which supply the water consumption of 280,000 inhabitants and industrial activities of Marseille harbor.

A database concerning hay's mineral content, dry matter, and climate dynamics

In addition, the geochemical variations of water composition during its pathway from irrigation channel till the phreatic aquifer were recorded and modeled. For modeling with PHREEQC software [7], we have defined a priori the processes, which can impact water chemistry, such as evaporation, dissolution, precipitation,

Nitrogen and phosphorus contents in hay increase from cut 1 to cut 3, whereas

Statistically, these results show a steady state of the production, which has been maintained, both in quantity and quality despite an average temperature increase of

For each chemical element measured in the waters, a model of fluxes is built up [6]. Activities and saturation indexes (*SI* = log Q − log K) were computed by using PHREEQC [7], using phreeqc.dat database: activity coefficients were computed with Debye-Hückel extended law, as ionic strength is small enough (*ca.* 0.01 M). The reaction of reduction of nitrate into ammonium was removed from the database as it is biologically mediated, and N(III) and N(V) were considered as distinct

On **Figure 6a** models for calcium are presented. At each step, where chemistry of water changes, the soil solution is computed. The time step is 2–3 months corresponding to the duration of hay growth for one cut. Thus, between solution S1 and S2, the evaporation of the water induced a loss of water and a concentration of the elements. Then, from S2 to S3, the pCO2 (partial pressure of CO2) of the soil, which is 30–100 times larger than in the outer atmosphere, results in acidification of solution and calcite dissolution. From S3 to S4, the model

*Nitrogen and total inorganic element contents in hay as function of the cut (from [9]). The mineral content of the hay is defined, per unit of dry matter expressed in percentage, by the sum of the content of the following* 

*elements: phosphorus, potassium, calcium, magnesium, sodium, iron, manganese, copper, and zinc.*

the potassium decreases significantly in cut 3. These results are explained by seasonal changes in the floristic composition of the hay [9]. But globally the total inorganic content in Crau hay increases over time from cut 1 to cut 3, and this order

**76**

**Figure 5.**

*(a) The pathway of calculation of fluxes of Ca during soil solution changes from surface irrigation water to groundwater; (b) for the 4 years of monitoring of water in Crau's area, comparison between measured and computed values of Na, Ca, Mg, C, K, S, and Cl for each cut (from [6]).*

simulated the fertilizer impact on the soil solution. Inorganic fertilizers (P, K) consist of gypsum CaSO4.2H2O, calcium dihydrogenphosphate Ca(H2PO4).2H2O, arcanite K2SO4, and sylvite KCl. The last three minerals were introduced in the database, with their thermodynamic properties [7C]. Dissolution of fertilizers was simulated by PHREEQC as the dissolution of a mixture of the above minerals. From S4 to S5, the model simulated the element uptake by plants. P absorption by plants was simulated as the removal of calcium phosphate from the solution, S absorption by plants as the removal of gypsum, and calcium being absorbed in excess to the sum of P and S, the remaining Ca absorption was simulated as a CaO removal from the solution; Na, K, and Mg absorption by plants were simulated respectively as the removal of Na2O, K2O, and MgO from the solution. Removal of elements by plant is computed by PHREEQC as a dissolution with negative coefficients, in the same way as evaporation is computed with a negative coefficient for water. To avoid transient negative concentrations, fertilizer dissolution was simulated before absorption by plants. In point S5, the soil solution is reequilibrated with the minerals of the aquifer.

The fluxes have been computed for the three cuts per year during 4 years of monitoring the water quality both in irrigation network and in groundwater (**Figure 6b**). All simulations are computed at the average temperature of

groundwater. With a R<sup>2</sup> larger than 0.96, regardless of the year or the cut, or the chemical element, the proposed model simulates very well the transformation of irrigation water into groundwater, describing for these 4 years a steady state.

Thus, our findings suggest that irrigation, both with the water inputs and quality of water, have played a key role for the sustainability of hay production till 60 years.
