Soil Urease Activity in Winter Wheat Residue Management Systems

Abstract

Surface residue accumulation under reduced and no‐till cropping systems has been shown to cause changes in the activities of several soil enzymes. The addition of crop residues containing urease increases the rate of urea hydrolysis which can increase the potential for ammonia volatilization. Our objective was to characterize the distribution of urease activity in the surface of two Oklahoma soils (Grant silt loam, fine, silty, mixed, thermic Udic Argiustoll and Norge clay loam, fine, silty, mixed, thermic Udic Paleustoll) which had been in conventional, reduced, and no‐till wheat (Triticum aestivum L.) residue management for four consecutive years. Soil cores 60‐mm deep were taken from residue management plots that had been previously fertilized with 168 kg urea‐N ha−1 yr−1 and separated into 10‐mm increments. Urease activity was determined in the soil increments and in mature undecomposed wheat straw. Urease activity was uniformly distributed in soil to a depth of 60 mm under conventional tillage. Significant increases in urease activity were measured in the surface 10 mm of both soils where accumulation of residue had occurred. Average urease activities in the surface 10 mm of soil under conventional, reduced, and no‐till residue management systems were, 12.1, 41.4, and 45.2 µg NH4‐N g−1 h−1 for Norge clay loam and 9.7, 12.4, and 35.0 µg NH4‐N g−1 h−1 for Grant silt loam, respectively. Activity of urease in mature undecomposed wheat straw grown at the site was 376 µg NH4‐N g−1 h−1 which was 28 × larger than the average activity found in soil. Wheat straw was shown to be a major source of the observed increase in enzymatic activity. Other sources for increased urease activity include increased microbial colonization during decomposition of residue and increased urea concentration in microsites due to fertilization, particularly in combination with residue.

Volatilização de amônia da ureia alterada por sistemas de preparo de solo e plantas de cobertura invernais no Centro-Sul do Paraná

“…esses resultados possivelmente se devam às diferentes características do solo, pois, como o estudo foi desenvolvido sob condições controladas, diferenças em temperatura e umidade do solo foram minimizadas e deixaram de ser fatores que influenciavam a volatilização de nH 3 . entre as variáveis de solo determinantes da maior volatilização de nH 3 em solos em pd, pode-se destacar a maior atividade da urease (Barreto & Westerman, 1989), a qual promove maior taxa de hidrólise da ureia, com consequente elevação do pH, o que potencializa a volatilização de nH 3 (Cantarella, 2007).…”

“…no presente estudo, desenvolvido em experimento de 28 anos, verificou-se maior atividade da urease na camada superficial (0-0,1 m) do solo em pd do que em pC (Quadro 3), a qual pode constituir-se num dos fatores determinantes da maior volatilização de nH 3 (Barreto & Westerman, 1989;rochette et al, 2009). a atividade da urease foi significativamente maior no pd nas quatro datas de avaliação (Quadro 3).…”

Ammonia volatilization in no-till system in the south-central region of the State of Paraná, Brazil

“…As a result, the pH of the soil surrounding the granules increases due to H + consumption, which increases NH 3 volatilization (Kissel et al, 1988). Thus, N volatilization is favored by high urease activity in the surface layer of no-tilled soils (Barreto & Westerman, 1989) and the presence of straw on the soil surface, which limits contact between the soil and the fertilizer (Menguel, 1996). However, high soil moisture, organic matter content and CEC levels in the surface layer of NT soils are important factors increasing the buffer capacity of soil pH variation (Vieira et al, 2008) with possible effects decreasing NH 3 volatilization (Ferguson et al, 1984).…”

Evaluation of microbial and enzymatic communities in soil and rizosphere from soybean plants

“…As reported by Vargas et al (2005), urease activity is higher in the no-tillage system, compared with the conventional system, due to the accumulation of organic matter over time. The urease enzyme activity in plantations with crop residues was approximately 30 times higher than that observed in conventionally cultivated soils, and these, when compared with soils under the no-tillage system, showed a four times lower urease enzyme activity (Barreto and Westerman, 1989).…”

“…2-B), because this enzyme is responsible for the hydrolysis of urea. The volatilisation of ammonia is favoured by the higher urease activity that is usually observed in the topsoil of no-tillage fields (Barreto and Westerman, 1989).…”