Predicting soil pH changes in response to application of urea and sheep urine.

Volatilization of NH3 following urea application or livestock urine deposition can result in significant loss of N to the environment. Urea hydrolysis to NH4 + results in an increase in pH, which in turn promotes transformation of NH4 + to NH3 . Accurately predicting changes in soil pH following urea (or urine) application will allow successful simulation of NH3 volatilization. The magnitude of the pH change depends on the soil's pH buffering capacity (pHBC). However, as actual pHBC values are not generally available, pHBC proxies (e.g., cation exchange capacity) have been used in modeling studies. In a 34-d laboratory incubation study, we measured soil pH and mineral N (NH4 + and NO3 - ) following a large application of urea (800 mg N kg-1 soil) to four soils with a range of pHBC values. In a second incubation, pH changes and mineral N dynamics were monitored in soil treated with sheep urine (773 mg N kg-1 soil) in the absence and presence of the nitrification inhibitor dicyandiamide. In both incubations, pH changes associated with urea hydrolysis and subsequent nitrification of NH4 + were predicted well using measured pHBC data. Our results confirmed that pHBC is base-type dependent (values greater when measured using KOH than NH4 OH). Soil pHBC is easily measured, and the use of a measured value (determined using NH4 OH) can improve model simulations of pH in the field and, potentially, lead to improved estimates of NH3 loss from animal-deposited urine patches and urea-treated soil.

Clinical trial of a new carbenoxolone analogue (BX24), zinc sulphate, and vitamin A in the treatment of gastric ulcer.

The effects of a new carbenoxolone analogue (BX24), zinc sulphate, and vitamin A on the healing of gastric ulcer have been assessed in a multifactorial clinical trial conducted in out-patients treated for four weeks.Forty-eight patients completed the trial. Three groups of eight patients were given respectively 300, 600, and 1 200 mg of BX24 daily and were compared with 24 patients who were given 300 mg of carbenoxolone sodium daily. The size of the ulcer niche was reduced on average by 14.6% in the eight patients given BX24 300 mg daily, by 47.6% in the patients given 600 mg daily, and by 51.0% in the patients given 1 200 mg daily. In the patients given carbenoxolone the size of the niche was reduced by 68.9%. These results were compared with those obtained previously with carbenoxolone and inert tablets and it was concluded that BX24 is without clinically useful effect in the doses used. Eleven of the 24 patients (46%) treated with carbenoxolone sodium developed side effects due to fluid retention and electrolyte disturbances. None of the patients given BX24 experienced such effects. In addition to carbenoxolone or BX24, 24 patients were given zinc sulphate, 660 mg daily, and in 24 patients these tablets were withheld. Among the patients given carbenoxolone the reduction in the size of the niche was much the same irrespective of whether or not the patients received zinc sulphate. Among the 12 patients given BX24 with zinc sulphate the ulcer healed completely in four and, on average, the size of the niche was reduced by 53.5%, compared with 21.9% in the 12 patients given BX24 alone. This difference is not statistically significant but the possibility of a beneficial effect from zinc is not excluded. No side effects attributable to zinc were observed.Twenty-four patients were also given vitamin A, 50 000 units daily, and in 24 patients the vitamin was withheld. No evidence was obtained to suggest that vitamin A had any beneficial effect on the healing of gastric ulcer.