No abstract

Manure application supplies plant nutrients, but also leads to trace element accumulation in soil. This study investigated total and EDTA-extractable B, Cd, Co, Cu and Zn in soil after 25 annual manure applications. The residual effect of 14 annual manure applications followed by 11 yr with no applications was also investigated. Manure was applied at 0, 30, 60 and 90 Mg ha(-1) yr(-1) (wet weight) under rainfed (treatments Mr0, Mr30, Mr60, and Mr90) and at 0, 60, 120 and 180 Mg ha(-1) yr(-1) under irrigated conditions (Mi0, Mi60, Mi120, and Mi180). The manure applications had no significant effect on soil B, Cd and Co content under both rainfed and irrigated conditions, but significantly increased total Cu and Zn content under irrigated conditions with Zn in Mi120 and Mi180 reaching the lower maximum concentration (MAC) level set by the European Community. Manure application also significantly increased EDTA-extractable Cd and Zn content in soil. Up to 27% of the total Cd (0.156 mg kg(-1)) and 21% of total Zn (38 mg kg(-1)) are found in EDTA-extractable form (Mi180 at 0-15 cm). EDTA-extractable Cd and Zn content was also significantly elevated in the irrigated residual plots due to the higher manure rates used. Thus, the impacts of cattle manure application on trace elements in soil are long lasting. Elevated Cd and Zn are a concern as other studies have linked them with certain types of cancers and human illnesses.

Enhanced phosphorus (P) release from soils to overlying water under flooded, anaerobic conditions has been well documented for noncalcareous and surface soils, but little information is available for calcareous and subsurface soils. We compared the magnitude of P released from 12 calcareous surface soils and corresponding subsurface soils to overlying water under flooded, anaerobic conditions and examined the reasons for the differences. Surface (0-15 cm) and subsurface (15-30 cm) soils were packed into vessels and flooded for 8 wk. Soil redox potential and concentrations of dissolved reactive phosphorus (DRP) and total dissolved Ca, Mg, Fe, and Mn in floodwater and pore water were measured weekly. Soil test P was significantly smaller in subsurface soils than in corresponding surface soils; thus, the P release to floodwater from subsurface soils was significantly less than from corresponding surface soils. Under anaerobic conditions, floodwater DRP concentration significantly increased in>80% of calcareous surface soils and in about 40% of subsurface soils. The increase in floodwater DRP concentration was 2- to 17-fold in surface soils but only 4- to 7-fold in subsurface soils. With time of flooding, molar ratios of Ca/P and Mg/P in floodwater increased, whereas Fe/P and Mn/P decreased, suggesting that resorption and/or reprecipitation of P took place involving Fe and Mn. Results indicate that P release to floodwater under anaerobic conditions was enhanced in most calcareous soils. Surface and subsurface calcareous soils in general behaved similarly in releasing P under flooded, anaerobic conditions, with concentrations released mainly governed by initial soil P concentrations.

AGRICULTURAL WATER QUALITY IN COLD ENVIRONMENTS SPECIAL SECTION Core Ideas• Floodwater DRP concentration increased with time of flooding in amended and unamended soils. • Increase in floodwater DRP concentration was less under simulated snowmelt than summer flooding. • Rate of P diffusion from pore water to floodwater was less under simulated snowmelt flooding. • Gypsum reduced floodwater DRP in one soil with DRP concentrations >1 mg L −1 , but not in the other. • Woodchip biochar was ineffective in reducing P release from soils to overlying floodwater.

A pot experiment was conducted on saline-sodic soil to compare and assess the reclamation ability of different amendments and amendment combinations based on soil quality parameters. Treatments prepared were; T1-control (soil only), T2-soil + 1% cow dung (CD), T3-soil + 1% partially burnt paddy husk (PH), T4-soil + gypsum (GYP)(100% Gypsum Requirement (GR), T5-soil + 1% CD + GYP (100% GR), T6-soil + 1% PH + GYP (100% GR). Organic amendments were applied at 1% of soil weight, and gypsum was applied at 100% gypsum requirement as surface application and incubated at room temperature (31±1 o C) for 90 days. After incubation, 42 days leaching was provided at a rate of 3 l/pot and the application was completed through 6 irrigation cycles/treatment with 7 days interval. After incubation and leaching of soils, onion variety Wallara-60 was grown in these pots. Results obtained both after the incubation and leaching show significant differences in bulk density, electrical conductivity (EC), pH, exchangeable Ca 2+ and Sodium Adsorption Ratio (SAR) among the treatments in comparison with the control. Among the treatments, the highest reduction in SAR (14.62 mmol/l) 1/2 and EC (1.71 dS/m) were recorded by the GYP+PH (T6). A significant difference was observed in the tiller number among the treatments. Treatments GYP (T4), CD+GYP (T5) and PH+GYP (T6) showed a significantly higher yield than that of control, while T5 and T6 showing the highest yield. Therefore, incorporation of partially burnt paddy husk and cow dung increased the effectiveness of gypsum in reclaiming saline-sodic soils. Further, the onion yield parameters supported the findings.

No abstract

Increased phosphorus (P) availability under flooded, anaerobic conditions may accelerate P loss from soils to water bodies. Existing knowledge on P release to floodwater from flooded soils is limited to summer conditions and/or room temperatures. Spring snowmelt runoff, which occurs under cold temperatures with frequent freeze-thaw events, is the dominant mode of P loss from agricultural lands to water bodies in the Canadian Prairies. This research examined the effects of temperature on P dynamics under flooded conditions in a laboratory study using five agricultural soils from Manitoba, Canada. The treatments were (a) freezing for 1 wk at −20 • C, thawing and flooding at 4 ± 1 • C (frozen, cold); (b) flooding unfrozen soil at 4 ± 1 • C (unfrozen, cold); and (c) flooding unfrozen soil at 20 ± 2 • C (warm). Pore water and surface water were collected weekly over 8 wk and analyzed for dissolved reactive phosphorus (DRP), pH, calcium, magnesium, iron (Fe), and manganese (Mn). Soils under warm flooding showed enhanced P release with significantly higher DRP concentrations in pore and surface floodwater compared with cold flooding of frozen and unfrozen soils.The development of anaerobic conditions was slow under cold flooding with only a slight decrease in Eh, whereas under warm flooding Eh declined sharply, favoring reductive dissolution reactions releasing P, Fe, and Mn. Pore water and floodwater DRP concentrations were similar between frozen and unfrozen soil under cold flooding, suggesting that one freeze-thaw event prior to flooding had minimal effect on P release under simulated snowmelt conditions. Abbreviations: DAF, days after flooding; DRP, dissolved reactive phosphorus.

Phosphorus (P) losses from flooded soils and subsequent transport to waterways contribute to eutrophication of surface waters. This study evaluated the effectiveness of MnO2 and a zeolite Y amendment in reducing P release from flooded soils and explored the underlying mechanisms controlling P release. Unamended and amended (MnO2 or zeolite, surface-amended at 5 Mg ha–1) soil monoliths from four clayey–alkaline soils were flooded at 22 ± 2 °C for 56 days. Soil redox potential and dissolved reactive P (DRP), pH, and concentrations of major cations and anions in porewater and floodwater were analyzed periodically. Soil P speciation was simulated using Visual MINTEQ at 1, 28, and 56 days after flooding (DAF) and P K-edge X-ray absorption near-edge structure spectroscopy and sequential fractionation at 56 DAF. Porewater DRP increased with DAF and correlated negatively with pe+pH and positively with dissolved Fe. Reductive dissolution of Fe-associated P was the dominant mechanism of flooding-induced P release. The MnO2 amendment reduced porewater DRP by 30%–50% by favoring calcium phosphates (Ca–P) precipitation and delaying the reductive dissolution reactions. In three soils, the zeolite amendment at some DAF increased porewater and/or floodwater DRP through dissolution of Ca–P and thus was not effective in reducing P release from flooded soils.