The effects of direct drilling, shallow cultivation and ploughing on the growth of winter cereals (wheat and oats) are reported for the first 4 years of long-term experiments on two non-calcareous clay soils (stagnogleys), representative of soils occupying a large proportion of the cereal growing area of the U.K. These 4 years have been characterized by extreme contrasts in rainfall and wetness of the soil.
On a Lawford series soil, with 35% clay, although the treatments affected average grain yields none of the differences was large. With additional nitrogen fertilizer, the yield after direct drilling was significantly heavier by 6% than after ploughing. On the Denchworth series, with 50% clay, 4 year average yields were also similar after direct drilling and ploughing, but in individual years the treatments had large effects. In two wet years grain yields after direct drilling were 89 and 82% of those after ploughing, but in another year they exceeded by 16% those after ploughing, where lodging had restricted grain filling. In the unusually dry season of 1975–6 yields of winter wheat after direct drilling exceeded those after ploughing (by 14 and 6% on the Lawford and Denchworth soils respectively) and this was attributed to greater availability of water and deeper rooting in the spring. In a year of heavy wheat yields (1977–8) about 10t/ha was achieved on both soils irrespective of the method of cultivation. In this year, after prolonged wet soil conditions in winter, the response to additional nitrogen fertilizer was greater after direct drilling and shallow cultivation than after ploughing.
The concentration of nitrogen in the crops tended to be smaller throughout the growing season after direct drilling than after ploughing, especially on the Denchworth soil in the wettest season. The method of cultivation had no effect on the uptake of either phosphorus or potassium except on the heavier soil in the wettest year, when potassium uptake was restricted after direct drilling.
The results are discussed in relation to information on soil conditions and root growth also being obtained in these experiments.