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A series of experiments in vitro were conducted to increase the dry matter disappearance of rice straw.
In their previous paper, the authors reported nitrogen top-dressing applied after the full heading time. The dry matter disappearance of various kinds of rice straw cultivated by this method of top-dressing was estimated in a trial in vitro.
Another trial was carried out to examine urea, glucose, and ground grass hay added to rice straw for effect on the dry matter disappearance of rice straw.
Trial 1 on the effect of nitrogen top-dressing after the full heading time up on the dry matter disappearance of rice straw. Various kinds of ground rice straw with and without nitrogen top-dressing after the full heading time were as substrates. In the trial, 0.5g of each substrate was added to 50 ml of culture medium which was a 1:4 mixture of whole rumen liquor and McDougall's synthetic saliva as a buffer solution. The culture tubes were maintained in a water bath at 39°C in anaerobic and unanaerobic conditions with and without gas flow of carbon dioxide during the incubation period, respectively.
The dry matter disappearance of rice straw with nitrogen top-dressing after the full heading time increased more remarkably than tat of rice straw without nitrogen top-dressing. So it was concluded that the low dry matter disappearance of rice straw might chiefly be attributable to the low nitrogen content of rice straw. There was no definite trend in the changes of dry matter disappearance of rice straw induced by the difference in quantity of nitrogen top-dressing applied after the full heading time.
Trial 2 on the effects of urea and glucose added to rice straw up on the dry matter disappearance. Three substrates, control, D(3)-NL(4) and D(3)-NL(4) rice straw, were used in this trial. Control straw had been cultivated without nitrogen top-dressing after the full heading time, D(3)-NL(4) straw with 3 g on nitrogen per square meter applied 5 days after the full heading time, and D(3)-NL(4) straw with 3g of nitrogen per square meter applied 20 days after the full heading time. Washed suspensions of rumen bacteria in McDougall's synthetic saliva wee incubated at 39°C for 2 days, with a continuous flow of carbon dioxide.
The dry matter disappearance of D(3)-NL(4), rice straw increased by addition of glucose but never increased by addition of urea. The dry matter disappearance of control rice straw, however, increased remarkable by addition of urea. In all the kinds of rice straw, the dry matter disappearance increased remarkable by addition of both urea and glucose. In the straw of rice cultivated with nitrogen top-dressing, the dry matter disappearance was about 20 per cent higher than that in the straw of rice cultivated without nitrogen top-dressing.
Trial 3 on the effect of ground grass hay added to rice straw up on the dry matter disappearance. The dry matter disappearance of ground rice straw by addition of ground grass hay was measured in two stages of growth. Mixtures of ground rice straw and ground orchard grass hay, and mixtures of ground rice straw and ground ladino clover hay were used as substrates. The ratios of mixture were 9:1g, 8:2g. 7:3g, 6:4g, 5:5g, 4:6g, 3:7g, 2:8g, and 1:9g for both types of mixtures. The method of incubation used was the same as mentioned in trial 2.
The dry matter disappearance of rice straw varied remarkably with the type and stage of growth of grass hay added. It was estimated that about 30% and 60% were the most desirable rates of addition of orchard grass hay in the growing and heading stages, respectively, to cause the highest dry matter disappearance of rice straw, and that about 10% and 70% were the same rates on ladino clover hay in the growing and bloom stages respectively.
Trial 4 on the effect of water-soluble nitrogen compound in grass up on the dry matter disappearance of rice straw and cellulose and up on volatile fatty acid (VFA) production. Cellulose powder and ground rice straw were used as substrated. To 0.5g of each substrate was added 0.2g of glucose. The method of incubation used was the same as mentioned in trial 2.
Addition of such water-soluble nitrogen compound as contained in orchard grass in the growing stage increased the dry matter disappearance of both substrated, rice straw and cellulose, more distinctly that that in the heading stage. In the case of ladino clover, however, there was no difference in the dry loom matter disappearance of either substrate between the growing and stages. When the dry matter disappearance was compared between the two substrates, the addition of such water-soluble nitrogen compound as contained in ladino clover was more effective than that contained in orchard grass. A similar tendency was observed between VFA production and dry matter disappearance.