Portable X-ray Fluorescence (PXRF) Analysis of Total Metal(loid)s and Sequential Extraction of Bioavailable Arsenic in Agricultural Soils of Animas Watershed

The Animas River provides irrigation water in northwestern New Mexico and the Navajo Nation. Concerns regarding the river water quality arose on August 5, 2015, when approximately 11.35 million liters of heavy metal contaminated water was accidentally released from the Gold King Mine into the Animas River. This study sought to determine the total concentrations of 7 heavy metal(loid)s (As, Pb, and Zn as metals of concern and Fe, Mn, Ca, and Cu as metals of interest) using portable X-ray fluorescence (PXRF) in two agricultural fields and compare these values to Environmental Protection Agency (EPA) regional screening levels (RSL). Total concentrations of 6 out of 7 metals were below the RSL; only As exceeded the soil screening value of 7.07 mg kg−1 at some locations in the agricultural fields. We also determined water-soluble (WS) and exchangeable fractions (Ex) of As that might be available for agricultural crop uptake using sequential extractions. The WS-As ranged from 0.014 to 0.074 mg kg−1 and Ex-As ranged from 0.135 to 0.248 mg kg−1 and thus were less than 1 and 3% of the total As concentration respectively (ranging from 5.62 to 14.79 mg kg−1) and not considered a threat for plant tissue accumulation. While the concentrations of As observed in the agricultural fields may have exceeded screening levels, the As was not apparently plant available and its risk to crops was determined to be low.

Determination of Suitable Extractant for Estimating Plant Available Arsenic in Relation to Soil Properties and Predictability by Solubility-FIAM

Extractant for estimating plant available arsenic (As) in soil has not been universally established. Moreover, to assess and monitor the complex chemical behaviour of arsenic (As) in soil and subsequently its transfer in crops, a suitable extraction protocol considering the soil properties in relation to crop uptake is required. For this purpose, a pot experiment was conducted to evaluate the suitability of the extractants for determination of extractable As in soil and risk assessment by solubility-free ion activity model (FIAM) with rice (variety: Sushk Samrat) as the test crop. Soil in bulk was collected from six locations of Indo-Gangetic Plain of Bihar, India, varying in physicochemical properties to conduct the pot experiment using five doses of As (0, 10, 20, 40 and 80 mg kg−1). Six extractants namely 0.2 (M) NH4-oxalate, 0.05 (N) HCl + 0.025 (N) H2SO4, 0.5 (M) KH2PO4, 0.5 (N) NH4F, 0.5 (M) NaHCO3 and 0.5 (M) EDTA were used. The results revealed that 0.5 (M) KH2PO4 gave the best correlation with the soil properties and crop uptake and can be considered a suitable extractant of As. Regardless of the As dose and the soil type used, in rice tissue, concentration of As followed the order root > straw > leaf and grain. As high as 94% variation in As content in rice grain could be explained, when 0.5 (M) KH2PO4 extractable As is being used as input for solubility-FIAM. Extractable As cannot be determined by atomic absorption spectrophotometer (AAS) coupled with vapour generation accessory (VGA) when 0.5 (M) EDTA was used as an extractant.

Critical Level of Magnesium for Cowpea [Vigna unguiculata (L.) Walp.] in Ultisols of Kerala

Background: Ultisols are characterized by low pH, low cation exchange capacity and low base saturation due to dominance of kaolinite and oxides and hydrous oxides of iron and aluminium. Among the basic cations, magnesium has smaller ionic size and larger hydrated radius which limits binding of Mg to soil exchange sites. As a result the deficiency of magnesium is a common nutritional disorder in these soils due to leaching of bases under humid tropical conditions. The determination of critical level of magnesium in soil and plant helps to manage the nutrient deficiency and will help to avoid crop loss.Methods: A pot culture experiment was conducted to determine the critical level of magnesium for cowpea in Ultisols of Kerala during January 2019. Graded doses of magnesium were applied @ 5 mg kg-1 to 80 mg kg-1 of soil as magnesium carbonate along with recommended dose of fertilizers to evaluate the effect of applied magnesium on soil pH, available magnesium in soil, magnesium content in plant, crop uptake and yield.Result: Soil pH and available magnesium in soil recorded at flowering and harvest was highest where magnesium was applied @ 80 mg kg-1 of soil. Magnesium content in stem and leaves was found to increase with the levels of magnesium added. No significant variation in the content of magnesium in pods was recorded. Crop uptake (66.62 mg g-1) of magnesium and yield per plant (79.33 g plant-1) was highest in the treatment (T5) where magnesium was applied @ 10 mg kg-1 of soil. The critical level of magnesium determined by Cate and Nelson graphical method was found to be 75 mg kg-1 of available magnesium in soil and 0.38% in leaves of cowpea during flowering.

Using Soil Tests to Evaluate Plant Availability of Potassium in Soils

The purpose of this chapter is to describe how bioavailable soil K is assessed or predicted by soil tests. Soil testing commonly refers to the collection of a sample of soil representative of a field or agronomic management unit and, by way of extraction using chemical reagents, determination of the quantity of a nutrient that can be related to plant uptake or yield. Normally only a small fraction of the total quantity of the nutrient present in the soil is extracted during the procedure, but if that amount can be correlated with actual crop uptake or overall crop productivity, then the soil test is deemed to have useful predictive power.Soil tests are routinely used to guide applications of fertilizer to soil so that crop demand for nutrients can be met effectively and economically. Here, we summarize the procedures involved in collecting a representative soil sample for K analysis, outline how that sample should be prepared for laboratory analysis, highlight the principles and mode of action of routine soil tests, and explore some common issues that may confound the correlation between a soil K test result and plant K acquisition or crop yield. Soil testing methods are discussed in the context of their relationship to the different forms of soil K and the in-soil chemical processes that may change these forms into K that can be taken up by roots.

How Closely Is Potassium Mass Balance Related to Soil Test Changes?

The exchangeable fraction of soil potassium (K) has been viewed as the most important source of plant-available K, with other sources playing smaller roles that do not influence the predictive value of a soil test. Thus, as K mass balance changes, the soil test should change correspondingly to be associated with greater or reduced plant availability. However, soil test changes and the availability of K to plants are influenced by many other factors. This chapter reviews research on soil test K changes and the relation to crop uptake and yield. A mass-balance relationship is rarely achieved from the measurement of exchangeable K because of the potential for buffering of K removal from structural K in feldspars and from interlayer K in primary and secondary layer silicates. Similarly, surplus K additions can be fixed in interlayer positions in secondary layer silicates, or potentially sequestered in sparingly soluble neoformed secondary minerals, neither of which is measured as exchangeable K. In addition, soil moisture, temporal differences in exchangeable K with K uptake by crops, K leaching from residues, clay type, organic matter contribution to the soil CEC, and type of K amendment confound attempts to relate K additions and losses with an exchangeable K soil test. Research is needed to create regionally specific K soil test procedures that can predict crop response for a subset of clays and K-bearing minerals within specific cropping systems.

Maize (Zea mays L.) Response to Potassium Application and K+ Uptake in the Soil: A Review

Potassium (K) is among the essential macronutrients needed for plant growth and it’s also an extremely dynamic ion in both soil and plant systems. K+ moves intensely in a plant system but moderately in a soil system. The average soil deposits of K generally are plentiful, but their mainstreams are not readily available for crop uptake. Many researches have dealt with the response of crops to potassium application, but few literatures have tackled that of maize to available K and its uptake. This review seeks to discuss current progress concerning the relevance of K in maize crop production and its uptake; how this physiological action transforms into growth and yield. We have reviewed available studies on the content, roles of K in the soil-plant system and factors contributing to K uptake and transportation in plant. Also, the benefits of Potassium Solubilizing Microorganisms (KSMs) as an alternative or in combination with exchangeable K+ are reviewed. Furthermore, K deficiencies in maize causing constraint in physiological activities and rendering weak resistance to pests are also discussed. The current study indicates that intensive agricultural production has led to K nutrient limitation in organic or coarse-textured soil resulting in the reduction of available K reserves. However, an optimal application of K can prevent these fertilization imbalances, which will eventually increase soil fertility.

Changes in Soil Organic Carbon Under Continuous Farming

Cultivating a land without proper crop management may lead to diminished organic carbon. Thus, this study assesses the effects of long-term farming (2014 to 2018) on soil OC. This study was conducted in Share Farm II, Universiti Putra Malaysia Bintulu Sarawak Campus on a selected area that practiced crop rotation. Soil samples have been collected according to grid sampling techniques by beds row and inter-row, and are analysed for soil pH, OM, TOC, and total N. The results show a trend in the alleviation of soil acidity with 2018 > 2016 > 2014, however, there is a diminished of TOC as the year of cultivation increases from 3.42% to 1.87%. The results show insufficient crop residue that returns to the soil system which has been subjected to flash flood and poultry manure application. In return, C retention ability was reduced, which further limit OM capability to supply nutrients upon decomposition. The correlation analysis has revealed that different types of crop residue such as grass clippings that have been applied in 2016 may be another reason for the insufficient N availability (0.44%). Therefore, the quantity and quality of residues may affect the decomposition rate and provide a lower C/N ratio, which significantly affects the soil pH, total N, and other nutrients that are essential for crop uptake. Res. Agric., Livest. Fish.7(2): 175-181, August 2020

Dynamics of the Fertilizer Value Chain in Mozambique

Mozambique is characterized by low agricultural productivity, which is associated with low use of yield-enhancing agricultural inputs. Fertilizer application rate averaged 5.7 kg ha−1 in Mozambique during the period 2006 to 2015, considerably low by regional targets, yet constraints that affect fertilizer use have not been thoroughly investigated. This study examined the constraints on fertilizer value chains in Mozambique to contribute to fertilizer supply chain strengthening. We used a combination of multivariate analysis and descriptive methods. Our findings indicate that fertilizer use has both demand and supply constraints. Key demand-side constraints include liquidity challenges, limited awareness about the benefits of using fertilizer, and low market participation, while the main supply-side constraints include high transaction costs, limited access to finance, and lack of soil testing results and corresponding fertilizer recommendations by soil type and crop uptake. These results suggest that scaling up the input subsidy program through vouchers (either paper-based vouchers or e-vouchers) with demonstration plots and effective targeting could drive up smallholders’ demand for fertilizer and fertilizer supply by strengthening a sustainable network of wholesalers and retailers. This would likely boost agricultural productivity.

Variable impacts of contemporary versus legacy agricultural phosphorus on US river water quality

Phosphorus (P) fertilizer has contributed to the eutrophication of freshwater ecosystems. Watershed-based conservation programs aiming to reduce external P loading to surface waters have not resulted in significant water-quality improvements. One factor that can help explain the lack of water-quality response is remobilization of accumulated legacy (historical) P within the terrestrial-aquatic continuum, which can obscure the beneficial impacts of current conservation efforts. We examined how contemporary river P trends (between 1992 and 2012) responded to estimated changes in contemporary agricultural P balances [(fertilizer + manure inputs)—crop uptake and harvest removal] for 143 watersheds in the conterminous United States, while also developing a proxy estimate of legacy P contribution, which refers to anthropogenic P inputs before 1992. We concluded that legacy sources contributed to river export in 49 watersheds because mean contemporary river P export exceeded mean contemporary agricultural P balances. For the other 94 watersheds, agricultural P balances exceeded river P export, and our proxy estimate of legacy P was inconclusive. If legacy contributions occurred in these locations, they were likely small and dwarfed by contemporary P sources. Our continental-scale P mass balance results indicated that improved incentives and strategies are needed to promote the adoption of nutrient-conserving practices and reduce widespread contemporary P surpluses. However, a P surplus reduction is only 1 component of an effective nutrient plan as we found agricultural balances decreased in 91 watersheds with no consistent water-quality improvements, and balances increased in 52 watersheds with no consistent water-quality degradation.