Effect of saponins and plant extracts containing saponins on the recovery of ammonia during urea-ammoniation of wheat straw and fermentation kinetics of the treated straw

Abstract

Saponins of Quillaja saponaria bark and the water extract obtained on homogenization of Yucca schidigera plants were used during urea-ammoniation to reduce ammonia loss. In Expt 1, chaffed wheat straw (2–5 cm length) was urea-ammoniated (50 g kg⁻¹ urea, 400 g kg⁻¹ moisture) for 25 days at 37°C with and without Quillaja saponins (QS) or Yucca plant homogenate, YPH (corresponding to 1 and 2 g kg⁻¹Yucca powder). The crude protein (CP) content of untreated straw was 34 g kg⁻¹. After 25 days, CP values of 90 g kg⁻¹ (urea; no saponin), 82 and 86 g kg⁻¹ (urea+QS at 1 and 2 g kg⁻¹) and 102 and 92 g kg⁻¹ (urea+YPH at 1 and 2 g kg⁻¹) were obtained. The ammonia-nitrogen bound (as percentage of urea-nitrogen added) to straw after the treatment was 39 (urea; no saponin), 33 and 36 (urea+QS at 1 and 0·2 g kg⁻¹), and 47 and 40 (urea+YPE at 1 and 2 g kg⁻¹). As the extent of ammonia bound to straw was higher with Yucca plant powder, especially at 1 g kg⁻¹, Yucca plant powder at 0·75 and 1 g kg⁻¹ was used in Expt 2. In Expt 1, the Yucca plant extract was used after homogenization of the Yucca plant powder, which is not feasible at farm level. Therefore, two simpler approaches (overnight soaking of the powder in water (Yucca powder extracted, YPE) and mixing of Yucca powder with the straw followed by urea-ammoniation (Yucca powder, YP) were used besides homogenization. Otherwise, conditions for the urea-ammoniation treatment were similar to those in Expt 1. The ammonia–nitrogen bound (as percentage of urea-nitrogen added) to the straw varied from 47 to 54% in the presence of the Yucca plant powder, which was substantially higher than that observed in its absence (38%). The ammonia-binding efficiency of Yucca plant powder to the straw was highest at 1 g kg⁻¹. Among the three methods tried, addition of the Yucca powder to straw followed by treatment with urea was the easiest, and the binding efficiency was similar to that observed when using the powder after homogenization. In both experiments, the true dry matter- and NDF-digestibilities, calculated organic matter digestibility and metabolizable energy, as well as rate and potential extent of gas production, were significantly higher (P<0·05) in the treated straw than in the untreated straw. These values were affected neither by the source of the saponins nor the manner in which the Yucca powder was applied.