Emergence and Early Growth of Four Desmanthus Species in Three Alkaline Clay Soils

Tropical pasture legumes such as Desmanthus are expected to improve pasture productivity in the extensive grazing systems of Northern Australia. However, the soils in these areas are often hostile (e.g., hard-setting and nutrient-deficient), which reduces legume emergence and establishment. Furthermore, these soils are often not ameliorated with amendments such as gypsum or starter fertilisers before planting. A pot trial was conducted to investigate differences in the emergence and early growth of four Desmanthus species. The legumes were grown in three alkaline clay soils that were unamended or amended with either gypsum (1 t CaSO4.2H2O ha−1 equivalent), a starter MAP fertiliser (12 kg P ha−1 equivalent), or both gypsum and the starter fertiliser. Seedling emergence was recorded daily and shoot yield was determined after six weeks’ growth. Final seedling emergence (as a percentage of viable seeds) varied among the Desmanthus species (c.f. D. leptophyllus = 63%, D. pernambucanus = 68%, D. bicornutus = 85%, and D. virgatus = 86%). On average, across the treatments, gypsum increased seedling emergence by 15%, whereas the starter fertiliser had no effect. The shoot yields and shoot phosphorus content of the Desmanthus species generally increased in response to the starter fertiliser. The collective results demonstrated that there were differences in emergence and early growth among the four Desmanthus species, which indicates that Desmanthus cultivar selection may be important in the relatively hostile soils of Northern Australia. Gypsum was an effective amendment for seedling emergence, whereas the starter fertiliser was an effective amendment to increase legume productivity

Arsenic and Cadmium and Associated Risk in Farm Soils of the Dry Zone Sri Lanka where Chronic Kidney Disease of Unknown Etiology (CKDu) is Endemic

This study reports on a wide-scale, systematic sampling program over two consecutive years investigating As and Cd and associated implications for human health in farming areas of the dry zone, Sri Lanka, where chronic kidney disease with unknown etiology (CKDu) is endemic. Surface soil (0–15 cm), fertilizer and rice seed samples were collected in 2017 and 2018 from three CKDu affected areas [Medawachchiya (M), Padaviya (P) and Giradurukotte (G)], and a non-affected control site [Hambanthota (H)]. All inorganic fertilizer samples showed low As (−1) and Cd (−1) concentrations, less than European Union guideline values, and no correlation with soil concentrations. Arsenic (≤ 3.8 mg kg−1) and Cd (≤ 3.0 mg kg−1) in the 400 soil samples analyzed were low at all four locations, and soils were considered suitable for sensitive and agricultural use. A human health risk assessment demonstrated the As and Cd concentrations in surface soil provided no concern for non-carcinogenic risk, and negligible or acceptable carcinogenic risk for all locations sampled. The As and Cd in rice seeds harvested were also less than detection limits (−1). This work provides clarity around As and Cd baseline values in certain farm soils of the dry zone Sri Lanka, and no substantive evidence that the levels of As and Cd in the surface soils contribute to CKDu in local agricultural populations. Additional sampling of subsurface soil and water resources would satisfy some uncertainties with the risk assessment described

Arsenic and cadmium leaching in co-contaminated agronomic soil and the influence of high rainfall and amendments

Arsenic (As) and cadmium (Cd) co-contaminate agricultural systems worldwide and threaten water resources, food security and human health. This column leaching study examined As and Cd mobility in an acidic sandy loam Alfisol soil collected from the dry zone of Sri Lankafor four co-contaminant concentration combinations (spiked and 1 year aged As at 20 & 100 mg kg-1 with co-added Cd at 3 & 20 mg kg-1) i, and under the influence of high rainfall (RF), phosphorus fertilizer (P) and lime amendments. In almost all treatments a synergistic co-contaminant adsorption effect was evident which reduced leaching of both elements, significantly in the higher spiked soil concentration treatments. The magnitude of leaching decrease varied with treatment but was greater for As due to its weaker retention in the soil. The co-sorbing effects, evident even under RF, were attributed to electrostatic sorption interactions, the formation of ternary bridging complexes and surface precipitation at higher concentrations. Liming significantly retarded mobilisation of both elements in all treatments, whereas P enhanced As leaching but suppressed Cd leaching, and both amendments moderated co-contaminant effects. An antagonistic effect of Cd on As sorption was evident in two treatments which showed increased As leaching with added Cd: the RF low spike concentration treatment, accredited to washout of stable As–Cd soluble complexes; the P high concentration treatment considered due to P disruption of As–Cd bridging complexes. This work is important for effective risk mitigation in these widely occurring co-contaminated agronomic systems, and demonstrates a strong system effect on synergistic or antagonistic co-contaminant interactions