This paper describes a new method for estimating pasture yield in which the yields of random quadrats are rated with respect to a set of reference quadrats preselected in the field to provide a scale which is available for reference throughout the sampling. Three alternative calibration procedures are described based either on the dry matter yields of the reference quadrats or on the yields of quadrats rated and cut either during or at the end of sampling. The second and third procedures are shown to have advantages over the first. When testing the method with four observers and two types of calibration scales, estimates of mean yield were generally within 4 per cent of the actual mean with a maximum difference of 8 per cent. Methods are given for calculating the number of samples required to obtain minimum variance for the estimate of mean yield for a given cost in terms cf time spent in the field.

A method is presented which gives an accurate estimate of the botanical composition of grassland on a dry-weight basis, without the necessity of cutting and hand-separating samples. In a number of quadrats an observer estimates which species take first, second, and third place in terms of dry-weight. The data are tabulated to give the proportion of quadrats in which each species received first, second, and third place. These proportions are multiplied by 70-2, 21-1, and 8-7, respectively, and added to give the dry-weight percentages of each species.The dry-weight-rank method was tested four times by comparing the results with those of hand-separating cut samples. No great differences between the two methods were detected when exact rankings, obtained from hand-separating, were used, and it was found that ranks could be estimated accurately, provided that sufficient training had been given to the observers.

A simple method is described of testing the susceptibility to acaricides of larvae of the cattle tick Boophilus microplus (Can.) in Queensland, Australia, by enclosing them in packets made from rectangular filter papers, folded once and secured along the remaining three sides by spring clips, that had been impregnated with Risella-oil solutions of DDT, dieldrin, or Bayer 21/199 (coumaphos), or with deposits from xylene solutions of Dilan. The response of susceptible engorged adult females to dieldrin was tested similarly. Five out of six experiments showed statistical evidence of repeatability of results in determination of relative DDT-resistance of larvae. There was a slight increase in susceptibility of non-resistant larvae to DDT with increasing age between 7 and 28 days for fresh packets but not for re-used packets. In three out of four tests, re-used packets were significantly more toxic (up to 1·40 times) to susceptible larvae than fresh packets. In one test a loss of toxicity occurred after storage of Bayer 21/199 packets for 23 days. The possible use of this method for measuring resistance in ticks is discussed.

Small additions of (15NH4)2SO4 and K15NO3 were used to investigate the nitrogen economy of Townsville lucerne (Stylosanthes humilis H.B.K.) and Rhodes grass (Chloris gayana Kunth.) grown separately and together in pots. Rhodes grass reduced the total yield of nitrogen per plant in associated Townsville lucerne to about half that of Townsville lucerne in pure stand. It appears that the Rhodes grass seedlings competed strongly with Townsville lucerne for available soil nitrogen during the first 5 weeks of the experiment. When the two species were grown together, Rhodes grass took up about 20 times as much 15N as the Townsville lucerne during the first 9 weeks, and about 8 times as much between 9 and 13 weeks after sowing. This ratio was the same for (15NH4)2SO4 as for K15NO3. When the two species were grown separately they took up equal amounts of 15N between 9 and 13 weeks after sowing. Estimates of soil nitrogen uptake at 5 weeks showed that 47% of the nitrogen in the Townsville lucerne growing with Rhodes grass had come from the soil. At 9 weeks the cumulative uptake of soil nitrogen by this Townsville lucerne was only 6%, and at 13 weeks only 3%, of its total nitrogen yield. No significant transfer of unlabelled nitrogen from legume to grass was detected. Attention is drawn to the assumption used in calculating uptake of soil nitrogen by the legume. It is suggested that this tracer technique can be applied to 15N experiments in the field.

Lack of information on the feeding value and on the presence of deleterious substances in many species belonging to the genus Indigofera has limited the potential use of these species as feed and fodder legumes. To obtain such information, leaves and seeds of 46 accessions representing 19 species of Indigofera that had shown some agronomic value were incorporated into a semi-synthetic diet at 5% w/w (seed) or 20% w/w (forage). The diets were fed to groups of young rats for 4 weeks, and dry matter intakes and growth rates relative to control diets were measured. Selected organs were examined for any histological changes. Seed and forage samples were analysed for indospicine, a hepatotoxin, and for the presence of another potentially deleterious substance, 3-nitropropanoic acid. Thirteen of the accessions representing 8 species were readily eaten and did not depress growth rates relative to control feeds, and another 13 representing 10 species gave acceptable growth rates. Liveweight gains were less affected by forage diets than by those containing seeds. With the exception of those in rats fed on diets containing I. spicata and I. nigritana, the organs of all other rats were histologically normal. It is unlikely that the concentration of 3-nitropropanoic acid (0.5-3.4 mg g-1 dry matter) in any feed was high enough to cause any of the observed toxic signs. Indospicine was present in only 4 of the 23 species tested, including all accessions of I. spicata, and the concentration of indospicine was a good indicator of the toxicity of these feeds. It is concluded that accessions that had produced growth rates comparable to those of controls may be recommended as non-toxic feeds suitable for further testing.