Responses of stream periphytic algae and benthic insects to increases in dissolved inorganic phosphorus (P) were assessed in a streamside mesocosm. Controls and treatments were colonized continuously in summer by biota from the stream. P was maintained in the treatments at 10 μg∙L−1, [Formula: see text] times the concentration in the controls. In the treatments the biomass of chlorophyll a reached 3.5 times that of the controls, accompanied by an increase in Cyanophyta relative to diatoms. No difference was detectable in the numbers of insects drifting from controls and treatments. Numbers of individuals emerging (> 40 species) from the treatments over 7 wk were 2.2 times those from the controls. In both controls and treatments, 77% or more of emerging insects were Chironomidae. After week 7 the density of benthic insects in the treatments, determined without size selection, was 1.75 times that of the controls; size distributions in treatments and controls were similar. Addition of P, therefore, increased the food of insects and resulted in a doubling of their survival to emergence.
Results are given for the effects of ammonium nitrate applied a t two levels and potassium sulphate a t one level on the nitrogen, calcium, magnesium, sodium, potassium, phosphorus, sulphur and chlorine content of perennial ryegrass grown pure and in the presence of clover. Three cuts were taken over two seasons and statistical analyses of the results are presented for each cut.Application of nitrogen fertilisers increased the K content of the ryegrass (chiefly the non-protein nitrogen). Sodium contents were increased a t all cuts and potassium in the second and third cuts, after application of nitrogen. Chlorine content was decreased and phosphorus increased (at second and third cuts). Variable magnesium contents were obtained, possibly due t o rainfall conditions. IntroductionA number of workers, including Bartlett et a1.l and Brouwer,2 have commented on the possible adverse effect of heavy dressings of nitrogenous and potassic fertilisers on grassland. These workers have stressed the probability of increasing the incidence of hypomagnesaemic tetany in ruminant animals grazing pastures overdosed with these fertilisers. Although a number of workers including Stewart & H~l m e s ,~ Bosch4 and Thomas & Thompson5 have provided valuable data on the effects of different manurial treatments on the mineral composition of grasses, there is still a considerable lack of information on the effects of fertiliser treatment with specific reference to magnesium.It is clear that the mineral composition of a sward is dependent on many factors other than the mineral status of the soil and such factors as botanical make-up, stage of growth, and season cannot be overlooked. In this investigation the effect on grass of two levels of nitrogenous fertiliser and one of potassium has been studied in herbage sampled at three different times of the year from replicated plots. Attention has been given to a single species, namely perennial ryegrass, although the effect of the presence of clover on the ryegrass has also been studied.
Abstract. To assess the merits of rearing coho salmon, Oncorhynchus kisutch (Walbaum), smolts semi‐naturally, trials were made in which 17 groups of tagged smolts, from 4 brood years, were raised on a partially natural diet in a semi‐natural habitat. Their subsequent survival, as determined from catch and escapement, was compared with that of four groups of smolts, from the same brood years, raised by a conventional hatchery method. The returns of the semi‐natural fish proved lower than or similar to those of the hatchery fish, which attained a maximum survival to catch and escapement of 26%. The survival of the semi‐natural fish showed no relation to their location in their linear rearing facility, nor to size of smolt (within a narrow range). Further trials showed that a month's delay in release of the semi‐natural fish did not increase returns, contrary to a current predictive model. The distribution of the catches of both kinds of fish was broadly similar in the troll and sport fisheries. It is concludedthat semi‐natural rearing of coho smolts is not superior to that of standard hatchery procedures, although it may be favoured for specific locations that lend themselves to this approach.
Main effects and interactions of nitrogen, phosphorus and potassium fertilisers and soil‐moisture tension on the growth, yield and phosphorus uptake of potatoes were studied in a field experiment. Yield, growth and nutrient uptake increases produced by applied N were interdependent with those produced by lowering soil‐moisture tension and were highly significant at all stages of growth. Increases in P uptake produced by N application at 60 lb. per acre and the lowering of moisture tension were attributed mainly to effects on root development. There was some evidence that the physiologically acid ammonium sulphate reduced the rate of fixation of applied P. Severe damage to roots and stolons by potassium chloride in the early season was reflected in reduced numbers of tubers. High N rates prolonged shoot development and delayed tuber development. Effects of potassium chloride on P uptake were small. The percentage of dry matter in tubers was considerably reduced by N and K applications and by lowering moisture tension, but was increased by applied P. Effects of applied P on P uptake were largely dependent on the presence of applied N and, as in previous work, soil‐P uptake was either depressed or unaffected by applied P. Dry matter yield/fertiliser rate curves were paraboloid in form, particularly in the early season.
4 series of field experiments was made on maincrop potatoes grown for seed with farniyard manure. The optimum rates of application of ammonium sulphate, superphosphate and potassium chloride were considerably lower than those at present practised in the area.Moderate applications of superphosphate (60 lb. of P,O, per acre) increased seed yield generally but had little effect with soils high in easily soluble phosphorus. Potassium chloride increased the ware/seecl ratio considerably. Interactions between the effects of the fertilisers on yield were very small.Use of 120 lb. of N per acre, consistently depressed yield of both ware and seed.
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