Single plants of Gabo, an Australian spring wheat, and Pitic 62, a Mexican semi-dwarf one, were grown at 20°C in a growth cabinet until anthesis. They were then transferred to glasshouses at 18/13, 21/16 and 24/19°C day/night temperatures and supplied with 20, 60 and 100% of their ad lib. water requirements. In terms of water use, dry matter production and grain yield, patterns of response to temperature and water stress were very similar for the two varieties. Highest yields were obtained at 21/16°C. Efficiencies of water use increased as water supply decreased; they were lower at 18/13°C than at higher temperatures. The amounts of dry matter produced after the treatments were imposed were taken as biological indexes of the nine environments. Over the entire range of those values, the grain yields of Pitic 62 were consistently higher than those of Gabo. Significant features of Pitic 62 that contributed to its higher yields were that: (1) by anthesis it had produced larger ears from a given weight of supporting shoot tissues; (2) after anthesis it mobilized a higher percentage and amount of stem and leaf material that apparently contributed to grain production. Two broad categories of shoots were distinguished. The first four shoots of both varieties were very tolerant of water stress, producing 50% of their potential grain yield on 20% of ad lib. water supplies. These shoots experienced water stress only after anthesis. Younger shoots experienced the stress treatments from an earlier stage of development; they were very sensitive to water stress and their grain yields were related linearly to water supply. Harvest index values varied with the category of shoot selected and with size of shoot or plant. Implications of relationships between grain weight and shoot weight for crop selection are discussed.

1. Fifty-one experiments on the nitrogen, phosphate and potash requirements of maincrop potatoes were carried out in Great Britain in 1956–62. Each experiment tested four rates of each nutrient in all combinations and both total and riddled yields and quality data were obtained.2. Nitrogen requirement was influenced by previous cropping and the rainfall during the preceding winter. 50–80 lb/acre of N are recommended in mixed farming rotations depending on winter rainfall, and 120–150 lb/acre of N in arable rotations.3. Yield increases from phosphate were usually larger on soils with low citric-soluble phosphate. Nevertheless, irrespective of soil phosphate status, optimum rates of application were at least 120 lb/acre of P2O5 which was the highest rate tested in most of the experiments.

Birch et al.: Magnesium Requirements of CropsAbsorbance was measured on a Unicam SP500 spectrophotometer. Chromatograms were repeated several times : the results are as follows : Extract Method 1 1 2 2 PC TLC PC TLC No. of chromatograms 5 5 4 4 Mean absorbance at 500mp 0.621 0.601 0.986 0,985 R.m.s. deviation 0.009 0.010 0.030 0.012 Coefficient of variation 1 . 5 1 . 6 3.1 1 . 3 %In a series of 14 assays, each performed in triplicate by TLC, the coefficient of variation was in the range 0.3-3.2 %, with a mean coefficient of variation for the 14 assays of 1 -6%.McKeown & Mark3 quote pairs of results of assays of annatto extract which differ by 0-4%, the mean difference for the six pairs being 1.6%. In our hands, thin layer chromatography has proved as suitable as paper chromatography for the separation of bixin before assay. Reproducible results can be obtained very rapidly.In 43 experiments on a range of soils there was little indication that magnesium sulphate applied to the seedbed increased yield of cereals, potatoes or sugar beet. In one experiment only, on potatoes, a very high rate of muriate of potash induced magnesium deficiency. Different rates of ammonium sulphate, compared on cereals only, did not affect crop response to magnesium.The magnesium content of barley foliage and the effects of magnesium sulphate and ammonium sulphate on this content were shown to be related to soil potassium and magnesium levels. 77 No. of Crop expts. Series I Spring oats Spring barley Series 11 Winter oats Spring barley Treatments compared" KzO rate: 40, 120 K2O method: broadcast on seedbed Mg rate and method: nil combine drilled 12 broadcast on seedbed 12 combine drilled N rate: 20, 60 K2O rate: 40, 120 Mg rate: 0, 24 Series lTI (a) Potatoes 4 K 2 0 rate: 120, 360 Potatoes 9 K20 rate: 120, 360 Mg rate: 0, 24 Mg rate: 0, 24 Mg rate 6: as foliar spray with K 2 0 rate 360" Ma rate: 0. 24 (b) Sugar beet 5 K 2 0 rate: 80,240

From 4 weeks after germination, three defoliation regimes – undisturbed, cut to 3 cm above ground every 4 weeks, or cut to 1.5 cm every week – were imposed on small swards of subterranean clover cv. Tallarook grown at constant 20´C and a 10 hr day length of 23,700 1x intensity. The treatments induced marked differences in morphology, growth, and survival. Within 16 weeks from sowing 50% of uncut plants had died compared with 5% under weekly defoliation. The rate of 35S uptake was consistently higher in uncut swards, which were estimated to have produced over 60% more dry matter than defoliated swards, yet yielded some 30% less because of high rates of death and decay within them. An optimum leaf area index (LAI) of 2.5–3 for net photosynthesis resulted from the rapid decomposition of dead tissues. Photosynthetic efficiency increased with age in uncut swards, and respiration rates over all treatments were linearly related to total plant weight. Plants adapted to weekly cutting by developing a prostrate network of stolons with a dense population of sites of leaf production which led to rapid canopy development following defoliation, and increasing rates of 35S uptake as time progressed. Five times as many leaves were harvested as from the uncut treatment and 70% of the herbage was leaf, compared with 25% in uncut swards. After 8 weeks of cutting, the photosynthetic rate of ground cover left following defoliation was about two-thirds of that achieved by complete leaf cover. The usual confounding of LAI with age, and different susceptibilities of dead tissues within low and high density populations to decompose rapidly, may explain previous conflicting reports of whether or not optimum LAIS for growth exist in clover swards.

Methods are described and results reported of meteorological observations made during the irrigation seasons 1936–57 and 1957–58 at three stations in the Nanneella irrigation area (dimensions approximately 6 by 7 km²) and on a dry-land station nearby. The former stations are situated on irrigated pastures, whilst the latter is on a dry-land pasture. Irrigation gives rise to a decrease of air and soil temperatures and an increase of atmospheric humidity- near the surface of the earth. The magnitudes of these effects depend inter alia on the irrigation rate and the distance down wind in the irrigated area. In summer at an irrigation rate of approximately 0.3 cm/day the observed differences between the dry-land station and a station in the centre of the irrigation area amounted to: 1–2°C for air temperature at screen height (125 cm); approximately 10°C for soil temperatures (at depths of 5 and 30 cm); 5–10% for relative humidity at screen height; 0.5–1.5 mm Hg for vapour pressure at screen height. The differences quoted are for average values of the observed quantities taken over a period of 4 weeks. The observations are presented in more detail in graphical form.