Source-Pathway Separation of Multiple Contaminants during a Rainfall-Runoff Event in an Artificially Drained Agricultural Watershed

A watershed\u27s water quality is influenced by contaminant-transport pathways unique to each landscape. Accurate information on contaminant-pathways could provide a basis for mitigation through well-targeted approaches. This study determined dynamics of nitrate-N, total P, Escherichia coli, and sediment during a runoff event in Tipton Creek, Iowa. The watershed, under crop and livestock production, has extensive tile drainage discharging through an alluvial valley. A September 2006 storm yielded 5.9 mm of discharge during the ensuing 7 d, which was monitored at the outlet (19,850 ha), two tile-drainage outfalls (total 1856 ha), and a runoff flume (11 ha) within the sloped valley. Hydrograph separations indicated 13% of tile discharge was from surface intakes. Tile and outlet nitrate-N loads were similar, verifying subsurface tiles dominate nitrate delivery. On a unit-area basis, tile total P and E. coli loads, respectively, were about half and 30% of the outlet\u27s; their rapid, synchronous timing showed surface intakes are an important pathway for both contaminants. Flume results indicated field runoff was a significant source of total P and E. coli loads, but not the dominant one. At the outlet, sediment, P, and E. coli were reasonably synchronous. Radionuclide activities of (7)Be and (210)Pb in suspended sediments showed sheet-and-rill erosion sourced only 22% of sediment contributions; therefore, channel sources dominated and were an important source of P and E. coli. The contaminants followed unique pathways, necessitating separate mitigation strategies. To comprehensively address water quality, erosion-control and nitrogen-management practices currently encouraged could be complemented by buffering surface intakes and stabilizing stream banks

Sorption and fractionation of dissolved organic matter and associated phosphorus in agricultural soil

Molibility of dissolved organic matter (DOM) strongly affects the export of nitrogen (N) and phosphorus (P) from oils to surface waters. To study the sorption an mobility of dissolved organic C and P (DOC, DOP) in soil, the pH-dependent sorption of DOM to samples from Ap, EB, and Bt horizons from a Danish agircultural Humic Hapludult was investigated and a kinetic model applicable in field-scale model tested. Sorption experiments of 1 to 72 h duration were conducted at two pH levels (pH 5.0 and 7.0) and six initial DOC concentrtions (0-4.7 mmol L-1). Most sorption/desorption occurred during the first few hours. Dissolved organic carbon and DOP sorption decreased strongly with increased pH and desorption dominated at pH 7, especially for DOC. Due to fractionation during DOM sorption/desorption at DOC concentrations up to 2 mmol L-1, the solution fraction of DOM was enriched in P indicating preferred leaching of DOP. The kinetics of sorption was expressed as a function of how far the solution DOC or DOP concentrations deviate from "equilibrium". The model was able to simulate the kinetics of DOC and DOP sorption/desorption at all concentrations investigated and at both pH levels making it useful for incorporation in field-scale models for quantifying DOC and DOP dynamics

Speciation of phosphorus in a fertilized, reduced-till soil system: in-field treatment incubation study

Citation: Khatiwada, Raju, Ganga M. Hettiarachchi, David B. Mengel, and Mingwei Fei. “Speciation of Phosphorus in a Fertilized, Reduced-Till Soil System: In-Field Treatment Incubation Study.” Soil Science Society of America Journal 76, no. 6 (2012): 2006–18. https://doi.org/10.2136/sssaj2011.0299.Phosphorus management in reduced-tillage systems is a great concern for farmers. Conclusive positive results of deep-banding P fertilizers compared with broadcast application and the chemistry of reduced-tillage systems remain unclear. Knowledge of the dominant solid P species present in soil following application of P fertilizers and the resulting potential P availability would help us understand and efficiently manage P in reduced-tillage systems. The objective of this research was to study the influence of placement (broadcast vs. deep-band P), fertilizer source (granular vs. liquid P), and time on the reaction products of P under field conditions. Changes in soil pH, resin-extractable P, total P, and speciation of P were determined at different distances from the point of fertilizer application at 5 wk and 6 mo after P application at a rate of 75 kg ha−1 to a soil system that was under long-term reduced tillage. Resin-extractable P was lower for broadcast treatments compared with deep-band treatments for both time periods. Resin-extractable P was greater in the liquid P-treated soils than in the granular P-treated soils. Speciation results showed that granular P fertilizers tended to form Fe–P-like forms, whereas liquid forms remained in adsorbed P-like forms in the soil 5 wk after application; moreover, speciation results showed granular P fertilizers precipitated less when deep-banded. During the 6-mo period following application, reaction products of broadcast granular, broadcast liquid, and deep-band granular fertilizers transformed to Ca-phosphate or mixtures of Ca-, Fe- and adsorbed-phosphate-like forms, whereas deep-band liquid P remained as mainly adsorbed P-like forms. Deep-banding of P would most likely provide a solution that is both agronomically and environmentally efficient for reduced-till farmers

Relict periglacial soils on Quaternary terraces in the central Ebro Basin (NE Spain)

Pedofeatures associated with ancient cold climatic conditions have been recognized in soils on terraces in the Monegros area (central Ebro Basin, Spain), at a latitude of 41°49′N and an altitude of 300 m a.s.l. Eleven soil profiles were described on fluvial deposits corresponding to the most extensive terrace (T5) of the Alcanadre River, Middle Pleistocene in age (MIS8–MIS7). Each soil horizon was sampled for physical, chemical, mineralogical and micromorphological analyses. Macromorphological features related to pedocryogenic processes were described: involutions, jacked stones, shattered stones, detached and vertically oriented carbonatic pendents, fragmented carbonatic crusts, laminar microstructures, succitic fabric, silt cappings on rock fragments and aggregates, and irregular, broken, discontinuous and deformed gravel and sandy pockets. Accumulations of Fe–Mn oxides, dissolution features on the surface of carbonatic stones, and calcitic accumulations were identified related to vadose–phreatic conditions. The observed periglacial features developed under cold environmental conditions in exceptional geomorphic and hydrological conditions. This soil information may have potential implications in studies of paleoclimate in the Ebro Valley as well as in other Mediterranean areas

Genetic studies of extra-early provitamin-A maize inbred lines and their hybrids in multiple environments

Open Access Article; Published online: 25 Sept 2019Vitamin A deficiency, drought, low soil nitrogen (low N) and Striga hermonthica parasitism of maize (Zea mays L.) cause malnutrition and food insecurity in sub-Saharan Africa. The objectives of this study were to determine combining abilities of extra-early provitamin A (PVA) lines, classify them into heterotic groups (HGs), identify testers, and determine yield stability of hybrids under contrasting environments in two trials. In trial 1, 20 extra-early PVA lines were inter-mated in a diallel mating scheme to obtain 190 F1 hybrids. The 190 F1 hybrids plus six checks were tested under Striga infestation, drought, and stress-free environments in Nigeria from 2015 to 2017. In trial 2, 35 extra-early yellow hybrids were evaluated under low-N, Striga-infested and stress-free environments in 2018. Provitamin A concentrations of 23.98 and 22.56 μg g-1 were obtained for TZEEIOR 202 and TZEEIOR 205. TZEEIOR 197 × TZEEIOR 205 (20.1 μg g-1) and TZEEIOR 202 × TZEEIOR 205 (22.7 μg g-1) contained about double the PVA level of the commercial check, TZEEI 58 × TZEE-Y Pop STR C5 (11.4 μgg-1). Both general (GCA) and specific (SCA) combining ability variances were statistically significant for most agronomic traits, although GCA was much larger than SCA effects, indicating that additive genetic effects primarily controlled the inheritance of those traits. TZEEIOR 97 and TZEEIOR 197 were identified as inbred testers. TZEEIOR 197 × TZEEIOR205 (20.1 μg g-1) was identified as a single-cross tester as well as the most stable and highest-yielding hybrid across environments. TZEEIOR 202 and TZEEIOR 205 should be invaluable resources for breeding for high PVA. PVA level was independent of hybrid yield potential, indicating that selection of superior hybrids with elevated PVA levels should be feasible

Nitrogen transfer from forage legumes to nine neighbouring plants in a multi-species grassland

Legumes play a crucial role in nitrogen supply to grass-legume mixtures for ruminant fodder. To quantify N transfer from legumes to neighbouring plants in multi-species grasslands we established a grass-legume-herb mixture on a loamy-sandy site in Denmark. White clover (Trifolium repens L.), red clover (Trifolium pratense L.) and lucerne (Medicago sativa L.) were leaf-labelled with 15N enriched urea during one growing season. N transfer to grasses (Lolium perenne L. and xfestulolium), white clover, red clover, lucerne, birdsfoot trefoil (Lotus corniculatus L.), chicory (Cichorium intybus L.), plantain (Plantago lanceolata L.), salad burnet (Sanguisorba minor L.)and caraway (Carum carvi L.) was assessed. Neighbouring plants contained greater amounts of N derived from white clover (4.8 gm-2) compared with red clover (2.2 gm-2) and lucerne (1.1 gm-2). Grasses having fibrous roots received greater amounts of N from legumes than dicotyledonous plants which generally have taproots. Slurry application mainly increased N transfer from legumes to grasses. During the growing season the three legumes transferred approximately 40 kg N ha-1 to neighbouring plants. Below-ground N transfer from legumes to neighbouring plants differed among nitrogen donors and nitrogen receivers and may depend on root characteristics and regrowth strategies of plant species in the multi-species grassland