Reduced cultivation for cereals


Cereals & Oilseeds
Project code:
01 January 2001 - 31 October 1988
AHDB Cereals & Oilseeds.
Project leader:
Soil Science Department Agricultural Development and Advisory Service Brooklands Avenue, Cambridge, CB2 2DR



About this project


During the last 15 years fixed costs on cereal farms have increased by about 40% in real terms while output from cereals has only risen by about 15%. Cereal prices are now static or falling and the scope for farmers to increase yield is small. In these circumstances the need to reduce fixed costs is urgent. The purpose of this review is to examine what is known about reduced tillage and to consider the opportunities that safer shallow tillage systems offer in reducing cost per ton of grain produced.

Britain has more recent experience of reduced primary cultivation than any other country and during the 1970's as much as 1/3 of the cereal area was established with these methods and without ploughing, thereby enabling a major switch to winter-sown cereals. This development was supported and encouraged by a very substantial investment in research and development undertaken by ICI, AFRC, ADAS and several universities.

Long-term experiments proved that well-managed shallow cultivation and direct drilling usually gave as good or better yields of winter sown crops as ploughing, and that the area capacity of these systems was much greater for the same input of labour and fuel. For the claylands in particular, straw burning and shallow tillage was successful in giving good quality seedbeds and much faster work rates, leading to uniform early establishment of crops.

However, early in the present decade, the majority of those farmers practising reduced tillage moved back to ploughing. There were probably three main reasons prompting this change: build-up of grass weed pressure in particular from brome; restrictions on straw burning; and compaction sustained during wet seasons and by repeated cultivation at one depth. Although these problems were apparent to researchers, results from experiments other than with surface straw did not highlight their effects because in general experiments were designed to avoid them.

A great deal of useful information has been gleaned from carefully monitored experiments and also from farm experience. Soil types found to give the best opportunity for reduced tillage were those with good drainage and stable structure, i.e. the ability to retain porosity without mechanical loosening. Thus, to the surprise of many, clay soils in drier areas proved superior to many free-draining light loams which tend to compact. At first the greater density of direct drilled topsoils was assumed to be an adverse feature, but research showed that in many cases extra continuity within the coarse pore/fissure system offset the lower total porosity and gave the added benefit of a better surface for movement of traffic. Climate was seen to playa major role in the success of reduced tillage. In the wetter northern arable areas of Britain only well-drained light loams were found to be suitable, in contrast to the findings in the drier south. This difference is related to the higher organic matter levels conferring extra structural stability in soils of the former areas.

When reduced tillage was first introduced drills and shallow cultivation equipment were inadequate. A wide range of effective equipment was developed for drilling into undisturbed ground, for shallow cultivation and for loosening to the depth of topsoil without lifting too many clods.

The insidious build-up of grass weeds in reduced tillage was at first dismissed as of minor importance but eventually it was recognised as one of the major limitations. Substantial effort has been invested into studying the dynamics of grass weed species which has led to a quantitative understanding of how husbandry changes influence weed pressure. This has proved useful in providing criteria for avoiding long-term build-up of viable seed.

Initially it was thought that reduced tillage was likely to increase the risk of foliar and root diseases carried over on crop debris. However, in practice few problems have been encountered and although the potential risk is still recognised, it is now evident that this is not a major risk in cultivation choice. However, the occurrence of cereal root disease is definitely enhanced by shallow incorporation of chopped straw and this is the subject of current studies.

The picture that emerged from more than a decade of research and farm practice is that successful reduced cultivation systems require careful planning and more flexible management than conventional systems. Many farmers did not invest this quality of management and allowed problems to build up to a severity which not only caused a substantial loss of yield but resulted in a permanent change of cultivation method.

Recent Developments 
Several recent developments point to the possibility of developing more robust systems of shallow cultivation. Tyre technology has improved so that now some general-purpose radial tyres can be used at recommended air pressure levels low enough to cause only small amounts of damage on wet soils. Research into all-purpose wide-span gantries is well advanced and brings nearer the prospect of economic zero- traffic cereal production. This could extend the opportunity for shallow tillage to a much wider soil and climatic range. The current development of a herbicide effective against brome grasses may overcome a major limitation of non-plough tillage.

There is little doubt that the contribution of shallow tillage to reducing the cost of cereal production could be much larger than at present. In particular, shallow tillage offers the opportunity for 'timeliness' with minimum input of resources. However, this aim would not be achieved were reduced cultivation to be used in the routine and in- flexible manner commonly practised in the 1970's. The section of the review entitled 'Strategies for Reduced Tillage' suggests ways in which farmers can take maximum advantage from shallow tillage systems while avoiding or minimising the drawbacks. Those farmers not prepared to invest this level of care are advised to stay with conventional farming methods.

Recommendations for Future Study 
Many of the questions and problems encountered through the application of shallow tillage have already been answered by earlier investigations. However, the review has identified a number of key areas needing further studies to take account of changing circumstances and to exploit new developments. These are assembled in the final section of the review and are summarised here:

'Low Pressure' Case Studies 
To encourage more effective adoption of low inflation pressure technology on farms and to investigate the problems which restrict uptake, it is recommended that several on-farm case studies are set up.

Wide-Span Gantries
The all-purpose gantry offers the prospect of zero-traffic cereal production which would minimise problems of soil and crop damage in wet seasons. It is recommended that continued support should be given to this engineering development. In addition complementary work on the maintenance of permanent wheelways is recommended for contrasting soil types. At a later stage of development case studies to monitor farm application and behaviour of different soils in zero traffic may become necessary.

Cultivation for Control of Water Erosion 
Concern about the extent of water erosion in Britain has recently increased. Conservation cultivation methods have proved effective for control in several countries and it is recommended that studies to develop similar methods that British farmers will adopt should be supported.

Practical Guidelines for Reduced Cultivation
To help those farmers that take up reduced tillage and to avoid the problems encountered in the past, it is recommended that a complementary effort is needed to develop detailed criteria for making specific on-farm decisions about use of implements, soil management and weed control.

Weed Studies
As growing systems change and new herbicides are introduced there is an urgent need for studies on weed behaviour and control methods.

Stubble Cultivation in the Presence of Chopped Straw
There is a dearth of information on the effect of stubble cultivation in the presence of straw mulch, and on blackgrass, brome and volunteer cereals. It is recommended that studies are undertaken in a range of situations with detailed monitoring of salient factors.

Brome Dormancy
It is recommended that investigations to identify the factors involved in the apparent dormancy of brome receive continued funding.

Volunteer Cereals
Cereal volunteers are frequently a problem to specialist cereal producers and it is recommended that studies on dormancy as the basis for improved control measures should continue to receive support.

Resistance to Herbicides 
It is recommended that continued support is given to estimating the distribution in Britain of resistant blackgrass a weed encouraged by reduced tillage. The support should extend to studies providing better understanding of inheritance of resistance in this species.

Root Diseases
It is recommended that support be given to studies to provide information on the effect of long-term straw incorporation by reduced cultivation on root rotting diseases which are encouraged by this practice.

This review, completed in October 1988 has 71 pages in the full article.