Manzoor Qadir

Phytoremediation of Sodic and Saline‐Sodic Soils

Sodicity-induced soil degradation is a major environmental constraint with severe negative impacts on agricultural productivity and sustainability in arid and semiarid regions. As an important category of salt-affected soils, sodic soils are characterized by excess levels of sodium ions (Naþ) in the soil solution phase as well as on the cation exchange complex, exhibiting unique structural problems as a result of certain physical processes (slaking, swelling, and dispersion of clay) and specific conditions (surface crusting and hardsetting). Saline-sodic soils, another category of salt-affected soils, are generally grouped with sodic soils because of several common properties and management approaches. Sodic and saline-sodic soils occur within the boundaries of at least 75 countries, and their extent has increased steadily in several major irrigation schemes throughout the world. The use of these soils for crop production is on the increase as they are a valuable resource that cannot be neglected, especially in areas where significant investments have already been made in irrigation infrastructure. It is imperative to find ways to improve sodic and saline-sodic soils to ensure that they are able to support highly productive land-use systems to meet the challenges of global food security.

EDTA-assisted Pb phytoextraction

Pb is one of the most widespread and metal pollutants in soil. It is generally concentrated in surface layers with only a minor portion of the total metal found in soil solution. Phytoextraction has been proposed as an inexpensive, sustainable, in situ plant-based technology that makes use of natural hyperaccumulators as well as high biomass producing crops to help rehabilitate soils contaminated with heavy metals without destructive effects on soil properties. The success of phytoextraction is determined by the amount of biomass, concentration of heavy metals in plant, and bioavailable fraction of heavy metals in the rooting medium. In general, metal hyperaccumulators are low biomass, slow growing plant species that are highly metal specific. For some metals such as Pb, there are no hyperaccumulator plant species known to date. Although high biomass-yielding non-hyperaccumulator plants lack an inherent ability to accumulate unusual concentrations of Pb, soil application of chelating agents such as EDTA has been proposed to enhance the metal concentration in above-ground harvestable plant parts through enhancing the metal solubility and translocation from roots to shoots. Leaching of metals due to enhanced mobility during EDTA-assisted phytoextraction has been demonstrated as one of the potential hazards associated with this technology. Due to environmental persistence of EDTA in combination with its strong chelating abilities, the scientific community is moving away from the use of EDTA in phytoextraction and is turning to less aggressive alternative strategies such as the use of organic acids or more degradable APCAs (aminopolycarboxylic acids). We have therefore arrived at a point in phytoremediation research history in which we need to distance ourselves from EDTA as a proposed soil amendment within the context of phytoextraction. However, valuable lessons are to be learned from over a decade of EDTA-assisted phytoremediation research when considering the implementation of more degradable alternatives in assisted phytoextraction practices.

Economics of salt-induced land degradation and restoration

Food security concerns and the scarcity of new productive land have put productivity enhancement of degraded lands back on the political agenda. In such a context, salt‐affected lands are a valuable resource that cannot be neglected nor easily abandoned even with their lower crop yields, especially in areas where significant investments have already been made in irrigation and drainage infrastructure. A review of previous studies shows a very limited number of highly variable estimates of the costs of salt‐induced land degradation combined with methodological and contextual differences. Simple extrapolation suggests that the global annual cost of salt‐induced land degradation in irrigated areas could be US

Reclamation of a saline-sodic soil by gypsum and Leptochloa fusca

27.3 billion because of lost crop production. We present selected case studies that highlight the potential for economic and environmental benefits of taking action to remediate salt‐affected lands. The findings indicate that it can be cost‐effective to invest in sustainable land management in countries confronting salt‐induced land degradation. Such investments in effective remediation of salt‐affected lands should form part of a broader strategy for food security and be defined in national action plans. This broader strategy is required to ensure the identification and effective removal of barriers to the adoption of sustainable land management, such as perverse subsidies. Whereas reversing salt‐induced land degradation would require several years, interim salinity management strategies could provide a pathway for effective remediation and further showcase the importance of reversing land degradation and the rewards of investing in sustainable land management.

Agricultural water management in water-starved countries: challenges and opportunities

Abstract Amelioration of sodic and saline-sodic soils by chemical amendments requires high capital input. Cultivation of salt tolerant grasses may mobilize the native lime (CaCO 3 ) in these soils through root action to substitute the chemical approach. A saline-sodic soil (pH s = 9.1, EC e = 9.8 dS m −1 , SAR = 103, CaCO 3 = 9.4%, CEC = 122 mmol c L −1 , texture = sandy clay loam) was experimented for reclamation. Concrete cylinders (60 cm long, 30 cm internal diameter) were used to prepare the soil columns. The bottom of each column was padded with a 5 cm layer of gravel and sand to facilitate leaching. In each lysimeter, soil was added in small increments to obtain a uniform soil column. The soil was packed to a height of 40 cm, making the soil depth in each column 35 cm. Four treatments, one cropped i.e. kallar grass ( Leptochloa fusca ) and three non-cropped (control, gypsum @ 50%, and 100% gypsum requirement) were leached with four leaching cycles (LC 1 to LC 4 ) at different time intervals. Canal water (EC =0.28 dS m −1 , SAR = 0.8) was used for leaching. Two leaching cycles, LC 2 and LC 3 , were completed during the peak growth of kallar grass (summer) and the remaining two, LC 1 and LC 4 , were completed during winter when its growth was very slow. After the completion of LC 4 , soil samples were collected from the lysimeters at 0–15 and 15–30 cm depths. The treatment receiving gypsum at higher rate (100% GR) removed the greatest amount of Na + from the soil columns and caused a substantial decrease in soil salinity (EC) and sodicity (SAR). Performance of the grass treatment in enhancing the leaching of Na + was between the gypsum treatments. Kallar grass removed more Na + during summer than during winter. Effectiveness of the treatments for soil reclamation was in the order: 100% GR > kallar grass > 50% GR > control.

Disposal and use of sewage on agricultural lands in Pakistan: a review.

Abstract Agriculture commands more water than any other activity on this planet. Although the total amount of water made available by the hydrologic cycle is enough to provide the world’s current population with adequate freshwater, most of this water is concentrated in specific regions, leaving other areas water-deficient. Because of the uneven distribution of water resources and population densities worldwide, water demands already exceed supplies in nearly 80 countries with more than 40% population of the world. Consequent to future population increase in these countries, supplies of good-quality irrigation water will further decrease due to increased municipal–industrial–agricultural competition. These facts reveal that the time has come for the sustainable management of available water resources based on global, regional, and site-specific strategic options: (1) understanding the concept of ‘virtual water’ and potential use of this water as a global solution to regional deficits, i.e. the water-short countries may import a portion of food crops or other commodities that require more water and export those that need less water in production; (2) improvement in current efficiencies of agricultural water use and conservation, both in the rain-fed and irrigated agriculture, i.e. to produce more with the existing resources with minimum deterioration of land and water resources; (3) use of efficient, economic, and environmentally acceptable methods for the amelioration of polluted waters and degraded soils, and (4) re-use of saline and/or sodic drainage waters via cyclic, blended, or sequential strategies for crop production systems, wherever possible and practical. We believe that these strategies will serve as the four pillars of integrated agricultural water management and their suitable combinations will be the key to future agricultural and economic growth and social wealth, particularly in regions that are deficient in freshwater supplies and are expected to become more deficient in future.

Chemical changes in a saline-sodic soil after gypsum application and cropping

Raw sewage is widely used on agricultural soils in urban areas of developing countries to meet water shortages. Although it is a good source of plant nutrients, such sewage also increases the heavy metal load to soils, which may impact the food chain. Management options for sewage contaminated soils includes addition of nontoxic compounds such as lime, calcium sulfate and organic matter, which form insoluble metal complexes, thus reducing metal phytoavailability to plants. In this paper we review the variation in irrigation quality of sewage at different sites and its impact on the quality of soils and vegetables. Although quality of sewage was highly variable at source, yet the effluent from food industries was relatively safe for irrigation. In comparison effluent samples collected from textile, dyeing, calendaring, steel industry, hospitals and clinical laboratories, foundries and tanneries were hazardous with respect to soluble salts, sodium adsorption ratio and heavy metals like zinc, copper, iron, manganese, nickel, cobalt and cadmium. The sewage quality in main drains was better than that at the industry outlet, but was still not safe for irrigation. In general, higher accumulation of metals in fruits and vegetable roots was recorded compared to that in plant leaves. Edible parts of vegetables (fruits and/or leaves) accumulated metals more than the permissible limits despite the soils contained ammonium bicarbonate diethylenetriaminepentaacetic acid extractable metals within a safe range. In either case further scientific investigations are needed to ensure safe management strategies. Cadmium appeared to be the most threatening metal especially in leafy vegetables. It is advisable to avoid leafy vegetables cultivation in sewage irrigated areas everywhere to restrict its entry into food chain.

Salt-tolerant forage cultivation on a saline-sodic field for biomass production and soil reclamation

Abstract Reclamation is needed on three million ha of slowly permeable saline-sodic soils in the Indus Plain of Pakistan. Previous studies measured an increased field-saturated hydraulic conductivity (Kfs) in the soil under study with cropping and gypsum application. This field experiment was conducted on a low permeability, saline-sodic soil (a fine-loamy, mixed thermic Typic Natrustalf) to compare the leaching of sodium and soluble salts and changes in chemical properties after various treatments. Treatments were: (i) perennial alfalfa (Madicago sativa L.), (ii) a rotation of sesbania [Sesbania bispinosa (Jacq.)W.F. Wright]-wheat (Triticum aestivum L.)-sesbania, (iii) incorporated wheat straw at 7.5 Mg ha−1 and (iv) a fallow control. These four treatments were each combined with and without 25 Mg ha−1 of gypsum and open-ditch drainage. Electrical conductivity (EC), pH, Na+, Ca2+, Mg2+ and Cl− of the soil in the saturated paste extract under each treatment were measured in each 20 cm increment to 120 cm after 6 month and 1 yr. Gypsum application increased the soluble Na+ in the top 20 cm soil. Poor internal drainage of the soil caused the exchanged Na+ to remain in the soil solution. However, one year after the treatments, the crop rotation with gypsum significantly decreased SAR, EC, pH and Cl− in the top 20 cm of soil. Alfalfa decreased these same parameters when compared to fallow in the top 80 cm of soil in gypsum-treated plots. The open-ditch drainage was not helpful in reclamation of this soil. In general, for surface soil improvement, a combination of added gypsum plus crop rotation was the best. For improvement of the deeper soil profile, gypsum plus alfalfa was the most effective of the treatments used.

Cadmium Concentration in Vegetables Grown on Urban Soils Irrigated with Untreated Municipal Sewage

Chemical reclamation of sodic and saline-sodic soils has become cost-intensive. Cultivation of plants tolerant of salinity and sodicity may mobilize the CaCO3 present in saline-sodic soils instead of using a chemical approach. Four forage plant species, sesbania (Sesbania aculeata), kallar grass (Leptochloa fusca), millet rice (Echinochloa colona) and finger millet (Eleusine coracana), were planted in a calcareous saline-sodic field (ECe = 9·6–11·0 dS m−1, SAR = 59·4–72·4). Other treatments included gypsum (equivalent to 100 per cent of the gypsum requirement of the 15 cm soil layer) and a control (no gypsum or crop). The crops were grown for 5 months. The performance of the treatments in terms of soil amelioration was in the order: Sesbania aculeata ≅ gypsum > Leptochloa fusca > Echinochloa colona > Elusine coracana > control. Biomass production by the plant species was found to be directly proportional to their reclamation efficiency. Sesbania aculeata produced 32·3 Mg forage ha−1, followed by Leptochloa fusca (24·6 Mg ha−1), Echinochloa colona (22·6 Mg ha−1) and Eleusine coracana (5·4 Mg ha−1). Sesbania aculeata emerged as the most suitable biotic material for cultivation on salt-affected soils to produce good-quality forage, and to reduce soil salination and sodication processes.

Potassium Substitution by Sodium in Plants

Cadmium (Cd) is considered as a potential toxin that is principally dispersed in natural and agricultural environments through anthropogenic sources. Untreated municipal sewage, often a potential source of Cd, is generally used to irrigate urban agricultural soils in many developing countries. A study was carried out to determine Cd concentration in untreated municipal sewage and sewage-irrigated soils and vegetables. The metal ion concentration in municipal sewage was found 3-fold (0.03 mg L−1) its permissible concentration in irrigation water (≤0.01 mg L−1). Ammonium bicarbonate–diethylene triamine pentaacetic acid NH4HCO3–DTPA) extractable Cd concentration in top 0.15 m soil ranged between 0.25 and 0.34 mg kg−1. Soil Cd concentration was significantly correlated with soil clay content, pH, electrical conductivity, and cation exchange capacity. Cadmium availability index (CDI) decreased with an increase in soil depth. The metal ion was found in leaf (0.17–0.24 mg kg−1 fresh weight) and fruit (0.07–0.18 mg kg−1 fresh weight) portions of all the sampled vegetables: bitter gourd (Momordica charantia L.), cauliflower (Brassica oleracea L.), eggplant (Solanum melongena L.), fenugreek (Trigonella foenumgraecum L.), okra [Abelmoschus esculentus (L.) Moench], onion (Allium cepa L.), pumpkin (Cucurbita pepo L.), and spinach (Spinacia oleracea L.). Leafy tissue accumulated Cd about twice that of the fruit portion. Our results suggest that prolonged ingestion of sewage-irrigated leafy vegetables can develop such Cd levels in human body that may cause a number of illnesses.