Use of p-benzoquinone and hydroquinone for retardation of urea hydrolysis in soils

Studies to evaluate p-benzoquinone (PBQ) and hydroquinone (HQ) for retardation of urea hydrolysis in soils showed that the effects of these compounds increase markedly with the amount of PBQ or HQ added and decrease markedly with time and with increase in temperature from 10 to 40°C. They also indicated that PBQ and HQ inhibit soil urease activity by identical mechanisms. The effects of various soil properties on the effectiveness of PBQ and HQ for retardation of urea hydrolysis in soils were investigated by studies with 25 surface soils selected to obtain a wide range in pH, texture and organic-matter content. Simple correlation analyses showed that the inhibitory effects of PBQ or HQ on urea hydrolysis in these soils were correlated very highly significantly with organic C content (r = - 0.76^***), total N content (r = - 0.74^***), urease activity (r = - 0.70 ^***) andcation-exchange capacity (r = - 0.62^***). The effects of these compounds also were highly significantly correlated with sand content (r = 0.57^**) and were significantly correlated with silt content (r = - 0.42*), clay content (r = - 0.49*) and surface area (r = - 0.49*), but were not significantly correlated with pH or CaCO₃ equivalent. Multiple-regression analyses indicated that the effectiveness of PBQ and HQ for retardation of urea hydrolysis in soils tends to increase with decrease in soil organicmatter content.