Nitrogen fixation by a subclover-grass mixture grown on two acid soils treated with lime

The effect of liming on symbiotic N2 fixation by subclover (Trifolium subteraneum) grown with ryegrass (Lolium multiflorum) was measured under glasshouse conditions using the 15N dilution technique. Two acid soils, a sand and a loam, were treated with two rates of lime or left unamended. In general, lime addition to both soils increased total dry matter yields, but in the loam, grass made up most of the increase, whereas in the sand, subclover made up all of the increase in dry matter. N2 fixation in both untreated soils was negligible. Lime addition increased the percentage N in the total herbage, had little effect on the proportion (Patm) and amount of N fixed by subclover grown on the loam, but dramatically increased both Pat, and the amount of N fixed by subclover growing in the sand. Subclover grown in the loam was poorly nodulated, despite the addition of large amounts of nodulaid (rhizobium survival in the soil was not a factor), but was well nodulated in the sand, thus explaining the lack of fixation in the loam. Higher amounts of inorganic N produced in the loam shortly after germination have the potential to inhibit nodulation in this soil. Also the loam, after liming but before planting, contained higher amounts of nitrate-N and total inorganic N than the sand, and the total inorganic N mineralized by the loam (518 versus 347 mg per pot by harvest) would also have had some effect on N2 fixation had nodulation taken place at a later date. Levels of critical nutrients (B, Ca, Cu, K, Mg, Mo and P) were measured in the clover tops, but no element appeared to be in deficit or excess, except A1 which could not be excluded as being at a toxic level in the limed loam in the present trial.

True protein digestibility and amounts of endogenous protein measured with the 15N-dilution technique in piglets fed on peas (Pisum sativum) and common beans (Phaseolus vulgaris)

The faecal and ileal true protein digestibilities of the raw pea (Pisum sativum) varieties finale and frijaune and the ileal true protein digestibility of steam-processed common beans (Phaseolus vulgaris) were measured in piglets using the 15N-dilution technique. The faecal true protein digestibility of both pea varieties was about 97. The ileal true protein digestibility was between 93 and 95, indicating that the pea protein is almost completely enzymically digested in the small intestine. The faecal apparent protein digestibility was 85 for both varieties while at the ileal level it was 79 and 74 respectively. The lower ileal apparent protein digestibility of peas can be attributed completely to the excretion of endogenous protein. The ileal apparent protein digestibility of toasted common beans was about zero (–4); the ileal true protein digestibility was about 66. This indicates that the protein of the common bean, although toasted, was highly resistant to enzymic digestion. It was calculated that per kg ingested bean protein, 340 g undigested bean protein and 700 g endogenous protein passed the terminal ileum. The results of the present study explain why in previous experiments a strongly reduced weight gain and even weight loss was observed in piglets fed on raw and toasted common beans.