Why copper and zinc are ineffective in reducing soil urease activity in New Zealand dairy-grazed pasture soils

Abstract

Micronutrients copper (Cu) and zinc (Zn) have the potential to inhibit soil urease activity (UA) and reduce ammonia (NH3) emissions over long duration (8–12 weeks) but have not been tested for reducing NH3 losses from cattle urine deposited in dairy-grazed pasture soils. The objective of this study was to assess the effectiveness and longevity of Cu and Zn in reducing soil UA, for the use of these metals to reduce NH3 emissions from deposited urine by grazing cattle. A series of experiments were conducted to (i) assess the relationship between inherent Cu and Zn status and soil UA of New Zealand dairy-grazed pasture soils, (ii) determine the impact of Cu and Zn addition to pasture soils on soil UA and (iii) investigate how soil organic carbon (C) and other C-related textural and mineralogical properties such as clay content and cation exchange capacity influence the effectiveness of added Cu and Zn in reducing urea hydrolysis. The results showed significant positive correlations of soil total C and total nitrogen (N) with soil UA. However, there were no significant negative correlations of soil UA with inherent Cu and Zn levels. Similarly, addition of Cu and Zn to soil did not significantly reduce soil UA. However, when Cu was added to two different soil supernatants there was a significant reduction in hydrolysis of urea applied at 120 and 600 mg urea-N kg–1 soil. Additions of Zn achieved negligible or small reductions in urea hydrolysis after 120 and 600 mg urea-N kg–1 soil applications to soil supernatants. This result suggests that Cu can inhibit soil UA and urea hydrolysis in soil supernatants with potentially low C, clay and cation exchangeable base contents. However, the interaction of bioavailable Cu with labile soil organic C and clay particles leads to its inactivation, resulting in ineffectiveness in organic C-rich pasture soils. Although most of the added Zn did not complex and remained bioavailable, the observed levels of bioavailable Zn had limited effect on soil UA.

Assessing the Impacts of Cu(OH)2 Nanopesticide and Ionic Copper on the Soil Enzyme Activity and Bacterial Community

“…In contrast, CuSO 4 addition at 5 mg kg –1 induced negligible effects on the activity of urease at 10 h (Figure a), even though the concentrations of bioavailable Cu in soil treated with CuSO 4 were higher than those with Cu­(OH) 2 nanopesticide or nano-Cu­(OH) 2 . Negligible changes in the activity of urease were also observed by Adhikari et al, who investigated effects of copper and zinc on urease activity in New Zealand dairy-grazed pasture soils. Here, measurable changes in the activity of urease were observed in soil treated with 50 mg kg –1 of CuSO 4 after 10 h of incubation (Figure a).…”

“…Metal-based manufactured nanomaterials, such as ZnO-NPs, CuO-NPs, and Ag-NPs, would likely release metal ions under aerobic conditions, which may impose impacts on soil bacteria, with changes in the activity of enzymes, such as acid phosphatase, , which is also highly dependent upon soil properties, such as organic matter content. For example, a recent study reported that additions of Cu to organic carbon-rich pasture soil achieved negligible reductions in urea hydrolysis as a result of the interaction of bioavailable Cu with labile soil organic carbon and clay particles . Nevertheless, no data were available to illustrate the impacts of a commercial Cu­(OH) 2 NPF on the soil enzyme activity and bacterial community, especially compared to its conventional ionic analogue CuSO 4 , restricting a comprehensive environmental risk assessment of the Cu­(OH) 2 nanopesticide.…”

“…For example, a recent study reported that additions of Cu to organic carbon-rich pasture soil achieved negligible reductions in urea hydrolysis as a result of the interaction of bioavailable Cu with labile soil organic carbon and clay particles. 24 Nevertheless, no data were available to illustrate the impacts of a commercial Cu(OH) 2 NPF on the soil enzyme activity and bacterial community, especially compared to its conventional ionic analogue CuSO 4 , restricting a comprehensive environmental risk assessment of the Cu(OH) 2 nanopesticide.…”

Biostimulant Effects of Micro Carbon Technology (MCT®)-Based Fertilizers on Soil and Capsicum annuum Culture in Growth Chamber and Field

“…Urease is the enzyme that catalyzes the hydrolysis of urea to carbon dioxide and ammonia. A large increase in the activity of this enzyme in a short period of time results in the loss of urea fertilizers due to its volatilization as ammonia, causing environmental pollution problems [34]. Since the highest increment was found for the SHFX treatment (Figure 1), the organic matter included in the TX product affected the microbiota in soils with good aeration.…”

Total and Available Micronutrient Status in Soils of Derived Savanna Ecology of Oyo State, Nigeria

“…They include iron, zinc, copper, boron, manganese, molybdenum, and chlorine. The micronutrient content of soils depends upon the soil types, parent material, soil pH, organic matter, clay content, amount of exchangeable bases, and phosphate [2,3].…”