Advance Note on Research

Abstract

The increased use of herbicides and minimum cultivation techniques for the establishment of crops has aroused further interest in sowings under trash or mulch. As part of a series of experiments on the effect of different mulches on seed germination and establishment and in view of disappointing results in the field when sowing into a paraquat-treated sward, it was decided to examine the eifect of such herbage on germinating seeds under glasshouse conditions. Part of a permanent pasture was sprayed with paraquat at the rate of 2 lb a.i. per acre. Samples of herbage were subsequently collected after 2, 7 and 14 days and stored in a deep-freeze until needed. Fifty seeds, per 10-in. diameter pot, of barley (Rika), perennial ryegrass (S321) or rape (Essex Giant) were sown on the surface of sterilized soil which had been saturated with water and allowed to drain freely for 24 hr. The seeds were then covered to a depth of l^-in. with herbage. The pots were watered daily, using a fine droplet sprayer, and notes were made on seedling numbers and growth characteristics. The results are shown in Tables 1, 2 and 3.Both crops and mulch treatments showed significant differences in emergence (Table 1).For all crops the shorter the interval between spraying and harvesting the mulch the greater was the depression of seedhng emergence.The growth of barley under the 7-and 14-day mulches could be regarded as satisfactory. With the 2-day mulch, growth was uneven and the first leaf of approximately 15-20% of the seedlings was white-tipped with yellowing along the veins. The seedlings were generally weakened and secondary infections, such as powdery mildew, were thus encouraged.The rape seedlings showed distinct symptoms of a physiological disorder under all treatments. The cotyledons had a white central vein, white edging and sometimes chlorotic spots. On a number of plants one cotyledon appeared to be more affected than the other, possibly due to shielding of one by the other during emergence. Formation of the true leaves appeared to be delayed on affected plants, and these true leaves also showed chlorotic areas. These adverse effects to growth occurred on approximately 90%, 60% and 20% of the plants growing in the 2-, 7-and 14-day mulches, respectively.Ryegrass was the slowest crop to emerge and gave the poorest total emergence. However, Table 1. Effect of mulch on the emergence of barley, rape and perennial ryegrass (angular transformation of % emergence)

Some effects of paraquat on crop establishment in killed swards

“…Experiment 3: effect of paraquat-treated grass mulch on germination and establishment In a previous experiment (Warboys & Ledson, 1964), phytotoxic effects were found when seeds were grown under mulches containing 250-700 ppm (dry-matter basis) of paraquat. In this experiment mulches obtained by sampling a permanent pasture 7, 14, 21 and 28 days after spraying with paraquat at 2 3 kg/ha contained 670, 362, 328 and 344 ppm respectively.…”

“…Residual paraquat activity in the soil was reported by Hammerton & Johnson (1962) when directdrilling rape and in trash by Warboys & Ledson (1964), despite an interval of up to 14 days between spraying paraquat and sowing seeds of rape {Brassica napus L.), barley {Hordeum vulgare L.) and perennial ryegrass {Lolium perenne L.). Gleeson (1964) andO'Toole (1965) also reported paraquat residues in grass reseeding trials on mineral and organic soils respectively, whilst Knight & Tomlinson (1967) found that paraquat was not always adsorbed by soils.…”

Factors Causing Losses during the Establishment of Surface-Sown Pastures

“…Although losses of seedlings due to soil fauna and residual herbicides were small by comparison with losses due to moisture stress, they can be important in other situations (Suckling, 1951). The effect of residual paraquat in cover can be overcome by allowing an interval of 1 to 2 weeks between spraying and sowing (Warboys and Ledson, 1965). To control slugs, Sucking (195 1) recommended grazing prior to sowing; but this would negate the advantages of cover.…”

Chemical Curing of Pinegrass With Atrazine and Paraquat

“…The samples were not analyzed for residual herbicide, but Warboys and Ledson (10) and sneva (7) For personal use only.…”