SP FAQ - Risk assessment
Yes it does. The saying 'You pays your money and takes your chances' is never more easily demonstrated than with no-tillage. Put another way lower risk systems almost invariably cost more than higher risk systems. What each operator must work out for themselves is how the cost of risks balances out against the cost of the inputs they are prepared to put into the system.
We have compiled a risk-assessment chart (see below) which identifies the six most important drill or opener functions that determine the risks associated with the use of any one type of no-tillage drill or opener. It ascribes values (1 10) to the risks associated with using different mechanical designs to perform each of these six functions, according to published scientific data. 1 is low risk. 10 is high risk. When you add all of the risk values together and express this as a percentage of the maximum attainable (60) you get a percentage-risk figure. The highest possible risk is 60/60 or 100%. The lowest possible risk is 6/60 or 10%. There is no such thing as zero risk in agriculture.
The percentage risk figure is an estimate of how many times you would expect to see an impaired crop in every 100 no-tillage crops sown with the machine in question. The figures produced by this chart have proven to be remarkably similar to field experience, so their relevance is high.
The table below lists some of the more common machine and opener types with risk assessments ascribed to them. The data are based on scientific experiments reported in the two books identified in Question 1. You may agree or disagree with them but unless you have actual scientific data that refutes them it would be unwise to change them markedly.
Examples of how some common no-tillage openers rank in terms of biological risk
|Disc version of winged opener||Vertical angled disc||Slanted angled disc||Shank & sweep openers||Vertical double disc||Simple winged tine|
|Seed depth control||2||1||1||9||3||8|
|Total out of max. 60||7||18||17||32||32||40|
|% chance of impaired biological performance||11%||30%||28%||53%||53%||67%|
(i) The 'Simple winged tine' (known as 'Baker Boot' ) and 'Disc version of winged opener' (Cross Slot®) were both invented by the authors and yet they find themselves at opposite ends of the risk assessment chart. In fact, the Cross Slot opener was invented to overcome the shortcomings of the 'Baker Boot' opener since although the latter scored well for 'Slot micro-environment' it scored poorly in most other respects.
(ii) The 'Baker Boot' was designed to be used predominantly in smooth pasture. Comparing this opener with other openers designed for arable no-tillage penalizes it unfairly but it is nevertheless included here without bias to illustrate how the table exposes the limitations of such an opener when used for arable no-tillage.
(iii) The figures represent the chances of obtaining impaired biological performance from using any of these openers. For example, the table suggests that use of Cross Slot openers will result in an 11% chance of a poor crop, whereas use of shank and sweep openers will result in a 53% chance of a poor crop unless there is little residue present and the fields are smooth and flat.
Put another way , the table suggests that in heavy residues on less-than-smooth ground there would be about 5 times as much chance of getting an impaired crop using shank or sweep type openers compared with Cross Slot openers.
The six key functions that appear in the chart are things every no-tillage opener or machine has to cope with every time it is used, or at least most times it is used in the case of 'residue handling' .
The table below lists some 29 desirable functions from 7 different no-tillage opener types that are ranked 1 - 5 according to how well each performs each function. In this table, it is clear that Cross Slot openers ('Combo winged tine & disc' ) are far superior to any other type of openers in existence.
No-tillage could be looked on as a short-cut. But it is only when you attempt to shortcut the short cut that risks get out of control.