Tillage and Conservation Agriculture

Abstract

Tillage is controversial but for generation after generation there was no debate: farmers ploughed as their forbears had ploughed, only more thoroughly. Pros: weeds and pests are controlled by breaking their life cycle—briefly; ploughing breaks up a crusted surface and compacted topsoil—briefly; creates a seed bed; and releases plant nutrients through mineralization of soil organic matter —this can also be a disadvantage. Cons: removal of surface cover and loss of soil structure renders the soil vulnerable to erosion; the habitat and life cycles of earthworms, mycorrhiza and myriad other beneficial soil organisms are disrupted; it compacts the plough sole and interferes with both drainage and up-flux of water; and it is costly in fuel and labour. On the Typical chernozem of the Bălţi Steppe , long-term field trials on different kinds of tillage, excluding zero tillage , show no difference in soil water stocks in spring, bulk density or crop yields ; but loss of soil organic matter was 1.6 times greater under the mouldboard plough compared with disking. Following the Dust Bowl in the 1930s, measures were developed to control erosive runoff : contour terraces , grassed waterways and the like. They have never been popular because the initial cost and continual upkeep are not recouped. Moreover, they don’t deal with the root cause; they allow business as usual but, when terraces are breached, the result is worse than before. The prime purpose of ploughing is to kill weeds ; desiccant herbicides made zero tillage a viable proposition and, since the 1960s, it has been adopted by farmers over 14% of the world’s cropland. It offers control of soil erosion , a simpler operation to manage, less outlay on machinery, more planting days, greater tolerance of drought , generally higher yields and, not least, a reduction of man-hours by nearly 70%. Growing out of these farmers ‘ experience, Conservation Agriculture (CA) encompasses no mechanical soil disturbance; continuous ground cover by crops or crop residues ; and crop diversification through rotations or associations of crops that control weeds , pests and disease. The new paradigm works almost everywhere for the simple reason that it eliminates destructive disturbance of the soil and daily attack by sun, wind and rain. But the first law of CA, often ignored, is remove all physical and chemical limitations before adopting no-till ; plough pans need to be broken up by deep cultivation. Retention of crop residues protects the surface and fuels life in the soil which, given half a chance, is self-sustaining; and ground cover of 70% usually eliminates soil erosion . Rotations should include perennial grasses and legumes for biological fixation of nitrogen to generate enough biomass to regenerate the soil. Excessive usage of pesticides under zero tillage is a myth—CA farmers use less and fewer chemicals than conventional farmers ; but precaution demands an alternative. Transition to CA is a complex process. It requires a period of transition for the improvement of soil quality , to enable the life of the soil to readjust, and for the farmer to learn how to manage the new system.

I have been a field for nigh on a thousand years, and I know men.

Some are clever, some are kind, but very few are clever and kind.

But he was. And I am sorry that all the other fields in England—who need him so much in these days—will have to go on without him.

Ronald Blyth: Obituary for a Suffolk farmer, 1930.