Studies on the weeds of vegetable crops. 5. Final observations on an experiment with different primary cultivations.
Annual determinations were made of the number of viable weed seeds in the soil on plots of a 9-year experiment with vegetable crops in which four primary cultivations and three manurial treatments were compared. The fluctuations in size and changes in species composition of the weed seed populations are described. There was little difference between deep ploughing and shallow ploughing with sub-soiling in the numbers of seeds present in the top 6in. of soil. Shallow ploughing alone resulted in rather greater numbers, especially after the production of fresh weed seeds. The highest numbers were consistently recorded on plots which had received shallow rotary cultivation, and the greatest contribution to this effect was made by Poa annua. In most species the number of seeds was not consistently related to manurial treatment, but in each year greater numbers of seeds of Stellaria media and Veronica persica were found where farmyard manure had been applied.
With Poa annua there was an interaction between the effects of manuring and those of primary cultivation, while most seeds of Polygonum aviculare occurred on plots which had received nitrogen fertilization only (See also Weed Abstr. 8: 598, 12: 1071, 1072 and 13: 473). Authors' summary.