A model is derived that relates yield to levels of applied fertilizer in terms of parameters that have direct physical meaning. N8, P8, and K8 define the contribution of the soil to the supply of nitrogen, phosphorus and potassium for plant growth; BN, BP and BK define the responses to nitrogen, phosphorus and potassium fertilizer at low nutrient levels and aN is the level of nitrogen required to raise the osmotic pressure sufficiently to prevent growth.

To test the model, field experiments were carried out on French beans and summer cabbage in which 125 different combinations of levels of nitrogen, phosphate and potassium fertilizers were applied. The yield data from each block of each experiment fitted the model very well. Fitted values differed from block to block but these differences could be attributed to the fact that for each block equally good fits were often obtained with widely differing parameter values. Estimates of N8 were made from chemical analysis of the (NH4 + NO3) — N of soil samples from the field plots, and P8, and K8 from chemical studies of the adsorption of phosphate and potassium on untreated soil. They were in substantial agreement with the average values obtained by the entirely different procedure of fitting the model to the yield data. Also estimated values for BN, BP and BK and aN from other chemical studies were consistent with those obtained by model fitting.

It is concluded that although the theory has limitations it is broadly in accord with the results of the detailed field experiments.

The systemic fungicide benomyl was used as a seed dressing and as a spray at two concentrations, 250 and 500 ppm, on the winter barley variety Pella. An additional treatment was a spray application of CCC at 500 ppm. All spray treatments were applied at growth stage 3–4. Without fungicide treatment, total yield in the inoculated plots was approximately 40% of that in the uninoculated plots. The 500 ppm fungicide-spray treatment significantly decreased incidence and severity scores of eyespot, the seed dressing being significant only for the latter. The seed dressing and 500 ppm spray treatments significantly increased mean yield/head, fertile tiller number and 1000 grain weight. All the fungicide treatments significantly increased total yield in the inoculated plots. There were no significant effects of CCC upon disease or upon yield, neither was there any interaction between benomyl and CCC.

The voluntary intake by sheep of seventy silages was measured in experiments in several years. Linear and multiple regression analyses were made between these voluntary intakes and the contents of dry matter, various acids and nitrogen and the digestibility value determined in vivo. There were some differences in these relationships for silages made from different groups of species, particularly those made from legumes. Voluntary intake was positively correlated with the contents of dry matter, nitrogen, lactic acid as a percentage of total acids and with the Flieg index. Voluntary intake was negatively correlated with the contents of acetic acid and ammonia as a percentage of total N. Although pH alone did not account for a significant part of the variation in intake, multiple regressions in which pH and one of the measurements of fermentation quality were included were significant, with pH positively related to intake. When all silages were considered, the correlation between voluntary intake and the apparent digestibility of dry matter was not significant. However, for legumes this correlation was significant and positive and for grasses other than ryegrass the correlation was significant and negative.

A perennial ryegrass silage was treated to give a range of acetic acid contents (2·0–8·8); pH and moistvire levels were held constant by adding solutions of the acid and of potassium hydroxide. When fed to sheep, ad libitum, the pattern of eating during the day was affected by acetate content in the silage but the intake over 24 h was unaffected. In a second experiment the infusion of acetic acid into the rumen depressed silage intake but this effect was not observed when part of the infusate was replaced by potassium acetate. It is considered unlikely that high acetate level per se will result in a low intake of silage.

Isocaloric quantities of casein, and glucose were infused into the abomasum and duodenum of sheep given perennial ryegrass silage ad libitum. Casein infusion significantly increased nitrogen retention but failed to affect silage consumption, suggesting that the positive relationship found between silage intake and silage nitrogen content is unlikely to be due to a low nitrogen status in sheep fed all-silage rations.

The pH of soil cropped with ryegrass increased with calcium nitrate as a fertilizer and decreased with ammonium nitrate, especially in the mid-range of pH. Changes above pH 7·2 and below pH 4·5 were small.

Yields of 4 cuts of grass given either N-fertilizer were similar over a pH range (in 0·01M-CaCl2) from 4·3 to 7·4. However, the composition of the grass and nutrient uptakes were affected by both soil pH and form of N-fertilizer.