Heavy metals in vegetables and their impact on the nutrient quality of vegetables: A review

Vegetables are vital to the human diet, and in particular provide the well-known nutrients to maintain normal physiological functions. The prolonged application of large amount of fertilizers and pesticides has resulted in heavy metal accumulation in vegetable gardens. Exposure to heavy metals by the consumption of contaminated vegetables and its toxicity is a serious concern. This article reviews the presence of heavy metals in different vegetables, their mechanism of absorption, impact of heavy metals on physiology, and nutrient reduction and associated impact on humans with emphasis on pregnant women based on the existing scientific literature. However, a limited number of studies was found in the data base that examined the reduction of nutrients in the vegetables due to heavy metal contamination. The heavy metals were found in 36 vegetables in 61 regions of the world and were above permissible limits in most of the vegetables. Specific study to human toxicity due to the contamination of heavy metals may be conducted with emphasis on pregnant women, children, and elderly people. Furthermore, strategy and policy should be devised to control the heavy metals in vegetables and those vegetables that are hyper-accumulators of heavy metals should be identified for awareness purposes.     

Amendment of Sugar Mill Wastewater Irrigation on Soil Biohydrological Properties and Yield of Vigna umguiculata L. Walp in Two Seasons

A field experiment was conducted to study the biohydrological properties of soil and yield of Vigna unguiculata L. Walp irrigated with five concentrations of sugar mill wastewater (SMW) during the Kharif and Zaid seasons. Among various concentrations of SMW, irrigation with 100% SMW significantly (P < 0.001) increased zinc (Zn), copper (Cu), cadmium (C), nickel (Ni), chromium (Cr), and iron (Fe) of the soil, while decreased total bacteria, fungi, actinomycetes, yeast, and rhizobia of the soil in both the cultivated seasons. However, the values of these metals were below the recommended permissible limit except Cd. Enrichment factor (Ef) of various heavy metals for soil was in the order Ni > Cr > Cd > Zn > Cu after irrigation with SMW. The crop yield of V. unguiculata was found to be inversely proportional to concentrations of SMW, with the best results being obtained at 50% SMW concentrations after 90 days of irrigation in both the cultivated seasons.     

Role of Some Plant Growth Promotory Bacteria on Enhanced Fe Uptake of Wheat

The quest for plant growth promotory bacteria that can help in sustainable agriculture has increased in the recent years owing to increasing cost of fertilizers. In the present study, the potential of three isolated bacteria having plant growth promotory effects in mobilizing the indigenous soil iron (Fe) in two different varieties of wheat was evaluated. Three bacterial isolates belonging to the genera Burkholderia and Acinetobacter were evaluated singly and in combinations for Fe uptake of wheat in a net house study. Results showed that bacterial isolates when used in combination performed better in comparison to their individual use. These isolates significantly increased the mean Fe concentration in grains and straw by 34.0% and 52.4% over the uninoculated controls and also increased the total Fe uptake per pot in comparison to uninoculated controls. The bacterial inoculation also showed a positive impact on the bioavailability of diethylenetriaminepentaacetic acid (DTPA) extractable Fe in soil.     

Productivity of capsicum influenced by conjoint application of isolated indigenous PGPR and chemical fertilizers

Inorganic fertilizers alone cannot sustain high levels of productivity. This study was conducted to determine whether higher productivity of capsicum could be achieved by conjoint application of chemical fertilizers and plant growth promoting rhizobacteria (PGPR). Four PGPR isolates (RS₂, RS₃, RS₄, and RS₇) from capsicum roots and rhizosphere were evaluated at Solan, Himachal Pradesh (India), during 2009–2012. Two best performers: RS₂ and RS₇ were tried singly or in consortium with different levels of chemical fertilizers under field conditions, Randomized Block Design, replicated thrice. The conjoint use of 100% recommended nitrogen, phosphorus, and potassium (NPK) doses through chemical fertilizers (RDF) plus PGPR significantly increased fruit yield, plant height, and biomass by 37%, 20%, and 30%, respectively, over sole application of 100% RDF (control). Further, response of capsicum to 80% RDF plus PGPR was statistically comparable with control. The results, therefore, indicate the potential of isolated PGPR strains to substitute about 20% NP fertilizers besides enhanced productivity of capsicum.     

Soil infiltration, runoff and sediment yield from a shallow soil with varied stone cover and intensity of rain

Stones on the surface of the soil enhance infiltration and protect the soil against erosion. They are often removed in modern mechanized agriculture, with unfortunate side‐effects. We evaluated experimentally the influence of surface stones on infiltration, runoff and erosion under field conditions using a portable rainfall simulator on bare natural soil in semi‐arid tropical India, because modernization and mechanization often lead to removal of these stones in this region. Four fields with varied cover of stones from 3 to 65% were exposed to three rainfall intensities (48.5, 89.2 and 136.8 mm hour^?1). Surface stones retarded surface runoff, increased final infiltration rates, and diminished sediment concentration and soil loss. The final infiltration ranged from 26 to 83% of rainfall when the rainfall intensity was 136.8 mm hour^?1. The reduction in runoff and soil erosion and increase in infiltration were more pronounced where stones rested on the soil surface than where they were buried in the surface layer. The sediment yield increased from 2 g l^?1 for 64.7% stone cover with rainfall of 48.5 mm hour^?1 to 70 g l^?1 for 3.5% stone cover with rain falling at 136.8 mm hour^?1. The soil loss rate was less than 2 t ha^?1 hour^?1 for the field with stone cover of 64.7% even when the rainfall intensity was increased to 136.8 mm hour^?1. The effects of stones on soil loss under the varied rainfall intensities were expressed mathematically. The particles in the sediment that ran off were mostly of silt size.     

Assessment of phytochemical and genetic diversity analysis of Plumbago zeylanica L. accessions

Genetic Resources and Crop Evolution - Selection of elite accessions is important to get the maximum quantity of bioactive compounds in medicinal plants. In this study, thirteen accessions...     

Nitrogen Mineralization as Influenced by Different Organic Manures in an Inceptisol in the Foothill Himalayas

Nitrogen-use efficiency can be enhanced through an understanding of the nitrogen (N) mineralization behavior of organic sources. An incubation study was conducted to assess the impact of organic manures on N mineralization. The manures, farmyard manure (FYM), Leucaena leucocephala, and poultry manure, were applied to the soil alone or along with urea. There was a rapid increase in the amount of mineral N released with a peak appearing either at 14 days (+urea treatments) or 21 days (manure only) of aerobic incubation. Thereafter the net N mineralized decreased gradually and levelled off beyond day 56. Overall the cumulative net N mineralized after 98 days of incubation was in the order urea > Leucaena + urea > poultry manure + urea _> FYM + urea > Leucaena > poultry manure > FYM > zero N. The potentially mineralizable N (N₀) was lower in treatments where urea was not applied.     

Direct and Residual Effects of Fly Ash-Based Integrated Fertilization on Rice (Oryza sativa L.) and Rapeseed (Brassica camprestris L.)

Integrated effects of fly ash (FA), farmyard manure (FYM), and chemical fertilizers recommended dose of fertilizer (RDF) on the performance of rice (Oryza sativa L.) and their residual effect on rapeseed (Brassica camprestris L. vartoria) were studied for two years in loamy acidic inceptisol of Assam, India.

The FA was generated from a bituminous and lignite coal-based captive thermal power plant of Hindustan Paper Corporation Ltd (HPCL), Assam. Rice yields were higher when FA, FYM, and RDF were used collectively vis-à-vis sole application of RDF reflected also in rapeseed under residual effect . FA effect on mean rice equivalent yield of the rice–rapeseed system was the highest (24.4%) under integrated application. Nickel (Ni) and cadmium (Cd) contents in rice decreased with increasing FA, while arsenic (As) was just the opposite. Integration of FA, FYM, and RDF was effective in lowering Ni, Cd, and As in rice compared to 100% RDF alone or together with FA. The residual effect on rapeseed was similar for Ni and As while the Cd content increased. Blending of FA, FYM, and RDF also positively altered the residual soil pH, organic carbon (C), and nitrogen, phosphorus, and potassium (NPK). Thus, FA can be an integral component of integrated plant nutrition system (IPNS) in augmenting crop yield and residual benefits in loamy acid inceptisol.     

Soil Quality Assessment under Restorative Soil Management Practices in Soybean (Glycine Max) after Six Years in Semi-Arid Tropical Black Lands of Central India

Vertisol soils of central India are heavy in texture, with high clay content and low organic matter. These soils are prone to degradation and the soil loss is due to poor management practices including excessive tillage. Based on a long-term study conducted for improving the quality of these soils, it was found that management practice such as low tillage (LT) + 4 t ha^?1 compost + herbicide (Hb) recorded significantly higher organic carbon (OC) (6.22 g kg^?1) and available N (188.5 kg ha^?1) compared to conventional tillage (CT) + recommended fertilizer (RF) + off-season tillage (OT) + hand weeding (HW) (OC: 4.71 g kg^?1, available nitrogen (N) (159.3 kg ha^?1). Among the physical soil quality parameters, mean weight diameter (MWD) was significantly higher under LT + 4 t ha^?1 straw + Hb (0.59 mm). The practice of LT + 4 t ha^?1 straw + HW recorded significantly higher microbial biomass carbon (MBC) (388.8 μg g^?1). The order of key indicators and their contribution towards soil quality was as follows: OC (29%) >, MBC (27%) > available zinc (Zn) (22%) > MWD (9%) > available boron (B) (8%), > dehydrogenase activity (DHA) (5%). The order of the best treatment which maintained soil quality index (SQI) values reasonably good (>1.5) was as follows: LT + 4t ha^?1 compost + HW (1.65) > LT + 4 t ha^?1 compost +Hb (1.60) > LT + 4t ha^?1 straw + HW (1.50). Hence, these treatments could be recommended to the farmers for maintaining higher soil quality in Vertisols under soybean system. Correlation studies revealed stronger relationship between key indicators like OC (R² = 0.627), MBC (R² = 0.884), available Zn (R² = 0.739) and DHA (R² = 0.604) with Relative Soil Quality Index (RSQI). The results of the present study would be highly useful to the researchers, farmers and land managers.     

Enhancing nutrient translocation,yields and water productivity of wheat under rice–wheat cropping system through zinc nutrition and residual effect of green manuring

Abstract

Efficient nutrient and water use are two important considerations to obtain good harvests of wheat. This necessitates the development of an effective nutrient management technique that not only increases yield, but simultaneously can save nutrient and water use. In this context, a field experiment was conducted at Indian Agricultural Research Institute, New Delhi, India to evaluate the residual effect of sesbania and rice bean (in-situ), subabul (ex-situ) green manuring and Zinc (Zn) fertilization, using chelated Zn-ethylenediaminetetraacetic acid (Zn-EDTA) on nutrient use, yields and water productivity of wheat under rice–wheat cropping system. Among residual effects of green manure crops and Zn fertilization, sesbania and foliar spray of 0.5% chelated Zn-EDTA at 20, 40, 60 and 80 days after sowing (DAS) recorded significantly higher nutrient content and uptake and yields than other green manure crops and Zn treatments. Residual effect of sesbania saved about 46.5?×?10³ and 30.5?×?10³ L irrigation water per tonne of wheat over subabul and rice bean, respectively. Foliar spray of 0.5% chelated Zn-EDTA at 20, 40, 60 and 80 DAS saved about 55.5?×?10³, 47?×?10³ and 13?×?10³ L irrigation water per tonne wheat over residual effect of 5?kg Zn ha^?1 through chelated Zn-EDTA as soil application, 2.5?kg Zn ha^?1 through chelated Zn-EDTA as soil application + 1 foliar spray of 0.5% chelated Zn-EDTA at flowering and foliar spray of 0.5% chelated Zn-EDTA at active tillering?+?flowering?+?grain filling, respectively. Correlation analysis showed positive correlation between Zn uptake and grain yield.