Mohamed Hachicha

EFFECTS OF SALINE WATER ON TOMATO UNDER SUBSURFACE DRIP IRRIGATION: NUTRITIONAL AND FOLIAR ASPECTS

A field experiment on the effects of drip irrigation (DI) and subsurface drip irrigation (SDI) with saline water (6.57 dS m -1 ) on three tomato cultivars (Lycopersicon esculentum Mill., cvs. Rio Tinto, Rio Grande and Nemador) was carried out with the purpose to quantify physiological responses. The aim was to improve irrigation water management under saline conditions of Tunisia. The trial was established in a siltclayey soil with three regimes of irrigation: 100 %, 85 % and 70 % of crop water requirement. Results evidenced a significant difference between the two irrigation systems for the three cultivars. Growth parameters such as leaf area, chlorophyll content and mineral composition of leaves, petioles, stems and roots were affected significantly by the different treatments, particularly for Rio Tinto and Nemador, being Rio Grande the more adapted. The fruit was the organ less affected. Strong accumulation of Na + and Cl - accompanied a reduction in Ca 2+ , K + , Mg 2+ and P content in the case of DI. The distribution of these last necessary elements for plants nutrition under a strong accumulation of Na + and Cl - depends on the cultivar and changes from one organ to another. SDI can be included as an effective option for tomato production in Tunisia.

Competitive sorption and desorption of trace elements by Tunisian Aridisols Calcorthids

The sorption and retention processes play an important role in determining the bioavaibility and fate of trace elements in soils. Sorption and desorption of Pb2+, Zn2+, Ni2+, Cu2+, and Co2+ in three Tunisian Aridisols Calcorthids (AR1, AR2, and AR3) were studied using batch experiments. Sorption and retention capacities were determined by means of Kr parameter and they were related to soil properties. The results showed that in all studied soils, Kr values for Pb2+ and Cu2+ were higher than those of Zn2+, Ni2+, and Co2+ indicating that soils have higher affinity for the first ones. The high sorption and retention capacity of the three studied soils is ascribed to their alkaline pH and their high carbonates contents favoring the precipitation of these elements. Moreover, bivariate correlation analysis showed that sorption and retention of the studied cations was also strongly correlated with clay fraction and Fe oxides contents. All soils show high sorption irreversibility of Pb2+, Zn2+, Ni2+, Cu2+, and Co2+. The soils with highest sorption capacity show also the highest irreversibility.

Using an Allometric Model for the Accumulation of Mineral Nutrients in Crops Under Saline and Water Stress: A Field Experience in Fertigation

Simulating accumulation of mineral nutrients in crops is useful for scheduling fertigation under ideal conditions, but doing so under saline and water stress would be a double beneficial tool. First, fertilization can be scheduled to fit mineral requirements while crops grow, and, second, fertilizers can be limited to the level determined by the stress condition, thus avoiding additional salinization by fertilizer not used by crops. The model considers crop development in a thermal timescale, in which the total crop period is obtained by integration in time of the thermal response equation. This integral is a constant value for a specific crop and cultivar. Biological age is then defined as a fraction of the current thermal time accumulated at any time to the total thermal time required. Using this relative time, the accumulation of mineral nutrients can be calculated as an allometric equation dependent on thermal time. It also considers crop biomass at any biological age, the total biomass of a crop and other specific parameters of the crop and the mineral nutrient being quantified (Misle J Plant Nutr 36:1327–1343, 2013). Thermal time dependence allows this model to follow daily variations of temperature in order to adjust the forecast of the accumulation of mineral nutrients to thermal variations on growth. The model is then coupled with already published equations for water and saline stress. As these restrictions are added to growth, total biomass will not be the maximum attainable for certain agro-climatic conditions, so that restrictions can be transmitted to the nutrient accumulation forecast (Misle and Garrido Determination of crop nutrient accumulation under water or saline stress through an allometric model, El-Zaiem Press, Cairo, Egypt, 2008). In this chapter we contextualize the problem, describe the theoretical background and analyse field experience from 1998 on crops fertigation, following stages of the model development and discussing growth restrictions imposed by saline and water stress to the nonrestricted forecast.

Improvement of Crop Production Under Saline Stress by a Biohydraulic Approach

One of the most restricting factors for horticultural production in the world, especially in arid and semiarid areas, is soil salinization. The “hydraulic” and “biological” approaches to this problem focus on the management, cultivation, or development of plants able to thrive on salt-affected soils by improved techniques of irrigation and innovative treatments to plants. This chapter reviews strategies by which plants can be enabled to grow on saline soils. The first component of this approach is based on irrigation methods as the subsurface drip irrigation (SDI), which is becoming popular, as it has revealed to be the most efficient irrigation system. The second component of our approach deals with selecting salt-tolerant lines/genotypes of potential crops and with new biological treatments to plants. For achieving this goal, it is necessary to gain deeper insight into the physiological/biochemical changes induced by the salt stress, which are attributable to detrimental effects of salt stress or are components of the adaptation mechanism. Indeed, exogenous applications of organic compounds and hormones as proline, polyamines, and brassinosteroids to plants under saline conditions have resulted in enhanced levels of these compounds, thereby improving the growth of plants and fruit yield. In addition, different crops differ in their response to exogenous application of these compounds because of their differing responsiveness to such applications. However, the use of such compounds seems to be plausible as components of the biohydraulic approach, so as to attain enhanced crop growth and yield under saline conditions.

Effect of Drip and Subsurface Drip Irrigation with Saline Water on Tomato Crop

With the purpose of improving salinity management and water use efficiency in agriculture, an experiment was carried out to study the effect of surface drip irrigation (DI) and subsurface drip irrigation (SDI) on a tomato crop (Lycopersicon esculentum Mill, cv. Heinz-2274) in a silty clayey soil with three irrigation water qualities: 3.0, 6.0 and 8.3 dS m−1. The results did not show any difference in the crop response of the two irrigation systems, whereas, the effect of the water quality was manifested. Saline water irrigation affected the tomato growth, in particular leaf area, dry matter, as well as the shoot/root ratios and the mineral composition of leaves, stems and roots. The accumulation of Na+ and Cl− was associated with a decrease in the contents of Ca2+, K+ and Mg2+, whereas, the P content in different organs remained constant. The more the salinity of the water irrigation rose, the more marked was the decrease in yield parameters of the tomato (setting, size, and yield). This experiment shows that in normal water management (100% of crop water requirement), the SDI does not present more advantages as compared with the DI for water whose electrical conductivity is not higher than 8.3 dS m−1.

Aloe vera long-term saline irrigation increases contents of hydrogen peroxide, lipid peroxidation and phenolic compounds

Salt stress is more and more becoming a serious problem in the world especially if we consider its damaging effect on the plant growth and yield. The cultivation of medicinal plants, such as Aloe vera, might be an alternative for the saline water use and salt-affected soils occupation. Aloe vera, commonly known as aloe, is one of the primary medicinal plants with multipurpose applications going from pharmaceutical to cosmetic aspects with a promising economic return. Aloe plants were cultivated and irrigated, for 14 months, with drinking water (C0) and with two levels of salt (C1 and C2). Changes in growth, hydrogen peroxide (H2O2), lipid peroxidation and phenolic compounds were examined in leaves at harvest. Depressive effects of salt irrigation on the plant growth parameters and a perturbation in inorganic ion contents were found especially with a high level of salt in the irrigation water. The intracellular oxidative stress was evaluated with the H2O2 production. Our results showed that the H2O2 content increased with the accumulation of the toxic ion (Na) in the leaf tissues. In addition, lipid peroxidation, measured by the malondialdehyde (MDA) level, increased as well with salt augmentation in the irrigation water. In response to salt stress, Aloe leaves showed a significant increase in the levels of phenolic compounds too. These results suggest that Aloe can be planted in soils affected by salinity and irrigated with salt water at least at a moderate concentration used in the present study.