Studies on the weeds of vegetable crops. V. Final observations on an experiment with different primary cultivations.
Annual determinations were made of the numbers of viable weed seeds in the soil on plots of a 9-year experiment with vegetable crops in which 4 primary cultivations [deep ploughing to 14-16 in. ; shallow ploughing to 6-7 in. ; shallow ploughing plussubsoiling to 16-18 in. ; and rotary cultivation to 6-7 in. using L-blades] and 3 manurial treatments [various arrangements of N only, FYM and NPK] were compared. During the first 6 years peas, spring cabbage, leeks and brussels sprouts were grown in a 3-year rotation; in the final cycle autumn lettuce and early summer cauliflowers replaced spring cabbage. 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 subsoiling in the numbers of seeds present in the top 6 in. 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 pérsica were found where FYM 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 N fertilizers only. [A.S. For part IV see H. A., 34: 4633.]-Nat. Veg. Res. Stat, Wellesbourne, Warwick.