Fernando Visconti

Prediction of the soil saturated paste extract salinity from extractable ions, cation exchange capacity, and anion exclusion

Process-based models could be used to predict the soil saturated extract salinity from extractable ion contents. However, a rigorous validation of such models for this purpose had not been carried out. A process-based model to predict the main inorganic ion composition, electrical conductivity, and pH of the saturated paste extract from extractable ion contents was developed step by step. The model development started from the principle of matter conservation in the soil solution as it concentrates from the 1:5 to the saturated paste extract. The need to include new hypotheses in the model was studied through calculation and analysis of standardised differences between measurements and model predictions. Therefore, best estimates of saturation paste extract properties occurred after taking into account the following: (i) free equilibration of the soil solution with the minerals calcite and gypsum under CO2 partial pressure of the saturated paste; (ii) further equilibration of the soil solution with the exchange complex; and (iii) determination of salt contents within the diffuse double layer (DDL) of the soil colloids, i.e. the anion exclusion. The last was necessary because the extracts where the determination of soil extractable anions (1:5 extracts), cations, and cation exchange capacity (CEC) were carried out were separated from their suspensions through centrifugation. Therefore, the reliable prediction of soil saturated paste extract salinity demands data on soil extractable ion contents, CEC, and the quantification of salts within the DDL. Additional keywords: agriculture, calcareous soil, irrigation, 1:5 extract, SALSOLCHEMEC, standardised difference.

A combined equation to estimate the soil pore-water electrical conductivity: calibration with the WET and 5TE sensors

Affordable, commercial dielectric sensors of the frequency domain reflectometry (FDR) and capacitance–conductance (CC) types estimate the dielectric permittivity (eb) and electrical conductivity (σb) of bulk soil. In this work, an equation was obtained to estimate the pore-water electrical conductivity (σp), which is closely related to the soil salinity in contact with plant roots, from eb and σb data, by combining the simplified dielectric mixing (SDM) model that relates eb to the soil volumetric water content (θ), with the Rhoades equation that relates θ and σb to σp. This equation was calibrated with measurements of eb and σb obtained with the Delta-T WET (FDR) and the Decagon 5TE (CC) sensors, in 20 pots filled with a clay loam soil and arranged as combinations of four levels of soil moisture with five levels of soil salinity. The calibrations were performed against reference θ and σp values. The σp was calculated with the chemical equilibrium model SALSOLCHEMEC and used as a more reliable reference than the electrical conductivity of the soil wetting water. For both sensors, the SDM model on the one hand, and the Rhoades equation on the other, provided the most accurate estimations using the least number of parameters regarding their respective alternatives, i.e. the third-order polynomial and the Hilhorst equation. The combined equation for estimation of σp subsequently provided root mean square deviations of 3.1 (WET) and 4.1 (5TE) dS m–1, which decreased to 1.5 and 2.6 dS m–1 for θ >0.22 m3 m–3, and σb 0.22 m3 m–3 and σb <3.7 dS m–1.

Advances in validating SALTIRSOIL at plot scale: First results

SALTIRSOIL (SALTs in IRrigated SOILs) is a model for the medium to long term simulation of soil salinity in irrigated, well-drained lands. Once the algorithms were verified, the objective of our study was to validate SALTIRSOIL under one of several water quality and management scenarios in Mediterranean agriculture. Because drip and surface are the most common irrigation systems in irrigated agriculture in Valencia (Spain), the validation was performed with climate, soil, irrigation water (composition and management) and crop (species and management) information from an experimental plot surface irrigated with well water and planted with watermelon that has been monitored since the late spring of 2007. To carry out the validation, first we performed a global sensitivity analysis (GSA). Second, we compared simulated soil saturation extract composition against measured data. According to the GSA, SALTIRSOIL calculations of soil salinity seem to be most affected by climate (rainfall and evapotranspiration) with 60% of explained soil salinity variance, water salinity with 26% of explained variance, and then irrigation with 4%. According to the closeness of the first comparisons between predictions and measurements, SALTIRSOIL does not seem to be affected by any systematic error, and as a consequence, neither inclusion of new parameters nor calibration of the others already included would be needed at least for surface irrigation. The validation of SALTIRSOIL continues under other water quality and irrigation management scenarios.

Predictive modelling of soil aluminium saturation as a basis for liming recommendations in vineyard acid soils under Mediterranean conditions

Abstract Soil acidification is a process of degradation that becomes more pronounced as a result of various human activities, but can be controlled through appropriate soil management. Calcium, magnesium and phosphorus deficiencies along with aluminium (Al) toxicity are considered the major constraints to plant growth in acid vineyard soils. The main aim of this work was to develop a model for liming amendment recommendation in acid vineyard soils using two liming materials, dolomite and sugar foam. These were used at three doses: 900, 1800 and 2700 kg ha−1 of calcium carbonate equivalent (CCE). Seven soil properties, namely pH in water, pH in 1 M potassium chloride (KCl), phosphorus content, base saturation, calcium, magnesium, potassium and aluminium exchangeable contents, were monitored at two soil depths (0–30 and 30–60 cm) during 3 years. The association among the soil properties, and with the soil acidity, was investigated through principal component analysis. This resulted in the selection of the aluminium saturation in effective cation exchange capacity (Al%ECEC) as the soil property to be modelled. According to the results of a subsequent analysis of variance (ANOVA), the Al%ECEC strongly depends on the dose (in CCE content) of the liming material independently of its dolomite or sugar foam nature. Besides, the dose effect is different depending on the soil depth and the sampling time. As a result, two quadratic models, one per soil depth and for the time of leaf drop stage, have been proposed to make liming recommendations in acid vineyard soils. These quadratic empirical models are comparable with the known linear Cochrane model using an f value between 1.5 and 2 in the range of doses studied, i.e. able to drop the exchangeable aluminium down to 50%. However, the models proposed in this work further provide (i) different dose recommendations for the arable and deeper soil layers, and (ii) confidence intervals for minimum and maximum additions of liming materials and, specifically, for these important soils dedicated to the growing of vines under Mediterranean conditions.

Soil, Water and Crop Management for Agricultural Profitability and Natural Resources Protection in Salt-Threatened Irrigated Lands

In the world areas under arid, semi-arid or dry subhumid climate, i.e. where potential evapotranspiration (ETp) exceeds rainfall (R), water scarcity imposes limits on agricultural diversity and productivity. Nevertheless, soils of high potential productivity are also often found under such climates, usually associated to river lowlands where fresh water proximity has allowed irrigation development to produce crops of high nutritional and economic value. It has been estimated that one sixth of world cultivated area is irrigated (AQUASTAT, 2008). What is more important, one third of world agricultural production comes from irrigated lands, and this fraction is going to significantly increase in the upcoming years (Winpenny, 2003). The main restriction to meet all of the soil productive potential of areas where ETp exceeds R is, in addition to water scarcity, soil salinity.

Persimmon (Diospyros kaki) Trees Responses to Restrictions in Water Amount and Quality

Abstract Persimmon cultivation is gaining importance in many semiarid areas of the world. In this chapter, existing information in the literature on persimmon water requirements and responses to variations in water supply and quality are summarized. It is concluded that persimmon water needs can be particularly high during summer, when the crop coefficient can reach values close to or even above 1.0. To cope with water scarcity, regulated deficit irrigation (RDI) has been shown as a useful technique for reducing fruit drop in persimmon trees. Late RDI strategies during fruit ripening can accelerate fruit color development resulting in earlier harvesting but with lower fruit weight. This chapter also provides important information on persimmon tree responses to salinity, along with methods to alleviate the detrimental impacts of low-quality irrigation waters on tree performance.

Electrical Conductivity Measurements in Agriculture: The Assessment of Soil Salinity

Soil salinity is an important issue constraining the productivity of irrigation agriculture around the world. The standard method for soil salinity assessment is based on a laboratory method that is cumbersome and gives rise to limitations for data-intensive works. The use of sensors for the assessment of the apparent electrical conductivity (EC) of soils offers a way to overcome these constraints. These sensors are based on three electromagnetic phenomena, namely, electrical resistivity, electromagnetic induction, and reflectome‐ try. Each class of sensors presents its own advantages and drawbacks. In the following chapter, these are presented along with the most popular commercial EC sensors used in nowadays agriculture, equations for the assessment of soil salinity on basis sensor measurements, some examples of application, and present and future development trends.