Geoscience Reference
In-Depth Information
lem because they could regrow from their strong underground rhizomes after the tops
had been killed by paraquat. However, the next generation of weedkillers included
glyphosate ('Roundup'), which was extremely effective in controlling these.
The pay-off for this reduced tillage was in allowing a major move away from
spring-sown crops and grass to winter cropping. Much larger areas could be sown
with higher yielding, and much more profitable, winter cereals. The extra money in
the farmer's pocket in the 1970s was invested in better drainage and better machinery
- a spiral of improvement. There were also some incidental benefits in the early
years. On heavy land, natural drainage and root development improved after direct
drilling because of the greater continuity of pores and channels that became estab-
lished through worm activity
(cf.
chapter 5
). On light land, the risk of soil erosion and
the loss of organic matter was reduced.
By the early 1980s, tine cultivators, chisel ploughs and direct drilling had re-
placed the traditional mouldboard plough on about 50% of the heavy land in the
drive towards quicker, more energy saving and more profitable agriculture. In farm-
ing terms, this represented a major revolution compared with 10-15 years previously
when the mouldboard plough reigned supreme. However, the new farming practice
had scarcely become established in the popular consciousness before its heyday was
already past.
There were serious disadvantages in reduced tillage that became evident after a
few years. In many cases, but particularly on light soils, the lack of ploughing led to
soil compaction below the shallow working depth. This was especially noticeable on
headlands and near field entrances, and led to substantial yield loss. The Agricultur-
al Development and Advisory Service (ADAS) now recommends loosening the soil
every few years to avoid this problem. Perhaps the major drawback of reduced till-
age was the increase in grass weeds in the growing crop, especially blackgrass
Alo-
pecurus myosuroides
and bromes; these are more difficult to control with selective
weedkillers than wild oats. The cumulative increase of bromes through the carry over
of seed from one year to the next was a major cause of the decline in direct drilling.
F
ERTILIZERS
Some 15 to 20 chemical elements are essential for plant growth, of which crops need
Of the major elements, carbon, hydrogen and oxygen are obtained from the air and
water (as CO
2
and H
2
O) while the others are mainly taken up by the roots from the
soil in the form of 'available' nutrient ions (
chapters 1
and
3
). Thanks to atmospheric
pollution, more than enough sulphur is supplied in 'acid rain' and dry deposition to
meet the needs of most crops except in parts of Scotland. However, these aerial inputs
