The trial described here for conducting on-farm compares wheat crops grown under three tillage systems: full or conventional tillage, minimal tillage and zero tillage.
First, it checks whether yield can be maintained using standard sowing dates but with the reduced effort and reduced expenditure associated with fewer tillage operations.
Second, it uses reduced tillage to open up the possibility for timelier sowing.
The trial also introduces a simple method for assessing how much of the rain falling on the crops is wasted or leads to soil erosion and how much goes towards producing crop growth. It uses the method to compare the three tillage systems for water efficiency.
Such a tillage trial could be important in areas where water is a major limitation to production and where soil structure is poor and erosion a problem.
It should not be attempted if aggressive local weeds cannot be controlled other than by full tillage. Nor should it be approached with the expectation that minimum and no-till approaches will increase yield unless they lead to timelier planting.
The aim will be long-term protection of the soil resource; reduced machinery wear and savings in fuel costs and labour.
A likely conclusion from this trial is that the farm will benefit from a mix of several tillage approaches. Other chapters you might need to refer to are those on choosing the right variety x sowing date, optimizing a cropping sequence for the farm, nitrogen use and crop establishment practices.
Those farms with low rainfall where normal cultivation results in high evaporative or runoff losses and therefore reduced soil moisture;
those farms where rain falls in bursts of high intensity leading to run-off;
those on steeply sloping land with associated problems of water erosion;
those with poorly structured soils that readily turn to dust when cultivated under dry conditions or form large clods when cultivated wet;
those with soils that readily form plough pans that are impenetrable to roots or with soils that become compacted under heavy wheeled traffic;
those farms requiring an early start to the season when weather may commonly preclude normal multi-pass tillage operations.
Tillage has been used for millennia to prepare the soil prior to sowing many of the annual grain crops. It involves applying power to break up and rearrange the entire topsoil structure. It has the primary aim of destroying weeds and pests but is also important for incorporating, redistributing or releasing nutrients and making the soil texture suitable for seed sowing, seed germination and for easy penetration of seedling roots.
The English word tillage is derived from the Old English tillen which means to toil. With only human or animal power available, it took a long time and much toil to till even moderate-sized areas of land. When tractors became available, larger areas could be cultivated per person.
Conventional multi-pass tillage
Tractors and their increasing power also made it possible to expand cropping areas into more difficult soils. In time this created problems in less robustly structured soils with many loamy and fine-textured topsoils weakening within a few years of tractors replacing animal teams for tillage. Fortunately, such weakening is reversible.
In the absence of tillage, structural stability of soil aggregates improves after several years under, for example, subterranean clover pasture.
Surface water runoff can increase following tillage on many soils, causing increased water erosion particularly on sloping cropland. Erosion by wind is also increased by tillage because the topsoil is left bare and loose.
Other potentially undesired effects of tillage include reducing soil organic matter through oxidation and deleterious effects on soil micro flora and fauna, also leading to reduced soil structural stability and increased surface runoff and water or wind erosion.
If it were possible to retain the desired effects of tillage while reducing or removing the problems it can generate, that would be a major step forward.
No-till cultivation is a major step forward for some situations but it can have its problems. It also disturbs the soil but limits that disturbance to rows or slots in which the crop seeds and fertilizer are placed.
Unfortunately, without herbicides no-till crops become dominated by weeds and so yield poorly. Herbicides have their associated costs and may have unknown side effects or long-term impacts on the environment. Furthermore, some weeds have developed resistance to some herbicides, leading to a need to rotate both crops and herbicide groups in order to keep crops weed-free.
On the positive side, a no-till system buries fewer fresh weed seeds and brings many fewer dormant weed seeds to the surface where they can germinate, so with increasing time under no-till, weed problems and herbicide applications can be reduced.
Minimum tillage took less time than conventional so the wheat crop (on right) could be sown earlier and in this case yielded more
H. GOMEZ MACPHERSON
Some advantages of no-till
A major plus of no-till sowing is that it can reduce erosion to low rates, close to those at which soil is formed from bedrock (0.01-0.001 mm depth of soil or about 15-150 kg soil ha-1 per year). Sustainable soils under cropping are therefore possible in the long-term, a difficult goal using conventional tillage particularly on slopes.
As well as making soil systems sustainable, no-till, when used intelligently, can also lead to improved yields. An example of this is where no-till has allowed earlier sowing than would have been possible if seeding were delayed through the time taken for multi pass tillage.
A no-till crop emerging uniformly
Sowing immediately following opening rains as is made possible by no-till, also means that any newly emerging weeds can be killed using low herbicide rates. Furthermore, soils are relatively warm during autumn sowing, and are typically wetting up with the onset of the cool, wet winters, making tillage less necessary to reduce soil strength. Soil disturbance below the seed zone using a tine set deeper than the seeder opener, typically improves crop establishment and yield.
A reduction in the number of cultivation passes as with no-till also means less wear on machinery, less use of fuel or animal power, less time devoted to soil preparation by the farmer thus a possible overall improvement in gross returns for the farm.
A further possible benefit of no-till over multi pass tillage is that rain, particularly heavy rain, is more likely to concentrate in the seeder slots and thereby penetrate directly to the crops root zone. This could improve not only water harvesting but also general water use efficiency by the crop. This contrasts with a more uniform penetration of water over the entire surface of a multi pass system providing benefits to inter row weeds.
However, where yields are high and large quantities of residues are left in the field after harvest, problems of disease and residue handling can become limitations to the no-till approach.
A trial conducted by the chapter author with wheat in western Australia compared conventional, minimal and zero-till systems for rainfall penetration over three years.
Using infiltrometers, described later for possible inclusion in your on-farm trial, it was found that it took three years before the zero-till treatment had settled and matured sufficiently to show benefits. Then, almost all (96 percent) of the 253 mm growing season rainfall penetrated the zero-till plots for use by the crop.
This was more infiltration than under minimum tillage (86 percent) but substantially more than under conventional tillage (79 percent) where 21percent of the rain ran off, was lost to the crop and caused soil erosion. Interestingly, earthworm numbers were increased tenfold by reducing levels of tillage as the soil micro fauna and flora rebuilt towards the situation in permanent pasture.
Conventional or full tillage rearranges the entire topsoil. It may require several passes to first turn the soil and then break it down into a friable seedbed prior to sowing.
No-tillage or zero-till involves one pass during which a part of the soil surface is disturbed or opened and the seeds are placed concurrently in that disturbed zone. The seeder opener may be a knife-point as little as 5 mm-wide on a tine, or a single, double or triple-disc set at a slight angle to the direction of travel.
Minimum tillage as defined here is generally a one-pass tillage operation at sowing synchronous with seed placement, typically achieved using full cut-out points, or full cut-out one-way or offset discs to break up the entire soil surface. It may include a shallow cultivation between seasons to control weeds when it may be called reduced tillage.
Conservation tillage is a generic term that covers any tillage system that reduces loss of soil and water compared with conventional tillage. Some have defined it more tightly to include treatment of residues specifying that at least 30 percent of the soil surface should be covered with residues after sowing so as to reduce erosion by water. It is likely to include zero, minimum and reduced tillage systems within the definition.
Tillage points 180 mm (left) and no-till points 12 mm, 50 mm winged, 50 mm winged with deep knives
No-till could reduce yield
It is possible that minimum or no tillage approaches will give lower yield than the conventional tillage operations used currently by the farmer.
A review of over 30 tillage trials (see further reading) found that tillage method (conventional or zero-till) did not change yield when data were averaged across studies, locations and years. However, in some places and some years either method could be far better (+1 t ha-1) or far worse (-1 t ha-1) than the other. The reasons for the variability were not always clear but in some cases reduced yield in the no-till treatments could be associated with slow early crop growth, more weeds, or increased soil disease particularly in wetter years. Increased yield in no-till treatments could sometimes be linked with improved aggregate stability and water infiltration and, where soil fertility was high, increased water storage and efficiency of water use.
The clear message is that there are many possible variables altering the relationships between tillage method and yield. The aim of the researcher and farmer should be to identify the limiting variables and adopt a tillage system or suit of systems that minimizes their effects.
Likely limitations to yield
The lesson for the design of your current trial is that you should ascertain with the collaborating farmer what are the likely limitations to the different levels of tillage. Discuss weeds, diseases, nutrition, problems of residues from previous crops, and soil factors perhaps limiting establishment. The design should include levels of likely limiting factors as subtreatments within the main tillage treatments.
Problems of stubble
Plant residues on or above the soil surface are often referred to as stubble. Most is likely to be dead straw remains of the previous wheat crop. Stubble handling can be an intractable problem of no-till and minimum-tillage seeder operation. The problem increases with increase in yield.
In theory, clean stubble on the soil surface should reduce water loss and when incorporated should increase soil organic matter, aeration and water retention and increase yield. Sometimes, however, retaining rather than removing stubble results in reduced yields.
FA double disc seeder
Strategies to capitalize on the positives of stubble (maximizing the time that stubble provides soil protection against wind and water erosion) while dealing with any negatives (disease, allelopathic and seeding problems) include straw spreading at harvest followed by flattening to enhance breakdown during the off season and heavy grazing.
Seeding through heavy stubble is difficult. Burning to remove the stubble makes seeding easier but it does waste crop nutrients and cause air pollution. Leaving standing stubble short at harvest may make it easier to sow into. Standing stubble wraps around tines less than straw lying on the soil. Disked seeders may cut through prostrate stubble on firm soil, but if the surface soil becomes soft, such as after rain, discs tend to push straw into the soil rather than cutting.
Methods of sowing into stubble include widening tine spacing on seeders. This allows greater amounts and lengths of straw to pass. Some farmers sow at up to 30 cm spacing to seed through the stubble and while still retaining it in order to reduce evaporation from the soil.
If stubble is going to be a major problem in the prospective trial, consider introducing stubble management approaches appropriate for the farm as subtreatments.
Problems of sowing and weed control
Soil disturbance prior to or during seed placement aims to ensure that sowing depth is optimal and consistent and that the seedling coleoptile can penetrate its covering of soil and the roots rapidly explore the soil to depth. Seeds sown at the wrong depth or at irregular depth because of poorly prepared cloddy soils or inadequate seeding equipment may produce poor yields. The other aim of soil disturbance is to set back or kill any weeds and pathogens that will restrain growth of the developing wheat seedlings.
For no or minimum tillage operations fertilizer is generally placed and not broadcast during sowing. Position is important. Fertilizer is best placed deeper than the seed through separate delivery tubes behind each sowing point, or slightly offset behind separate seed and fertilizer points in each sown row. Fertilizer toxicity to the cereal seedlings is thereby minimized and weed seeds germinating on the soil surface have their access to the deeply placed fertilizer delayed.
Putting fertilizers below the seed using a deep fertilizer point, followed by a shallower seeder point then a press wheel
The farm should be aware that for deep fertilizer placement power requirements on no-till seeders might be as high as with conventional seeders sowing into loosened tilled seedbeds. Typically, 3-6 kW may be required per knifepoint for a knifepoint to penetrate over 100 mm into the soil at a speed of about 8 km/hr. This may reduce the number of rows that the farmer can plant at once with normal machinery or animal power.
In your trial, type of fertilizer, timing and placement will depend on local constraints. As with other variables it may be appropriate to include a fertilizer subtreatment in the study.
Effective weed control is critical if minimum or no-till practices are to compete with conventional tillage in the production of yield. For your trial it may be advantageous to apply residual herbicides before sowing. In that case, the farmer should add knives to the seeder when sowing to throw soil and herbicide out of the sown row so the seedling can grow in relatively non-toxic soil. Weeds germinating between the sown rows receive the toxin from the thrown soil.
Depending on the farms previous experience with weed control methods, it may be necessary to include subtreatments in the trial with different types or levels of herbicide.
Questions before you start
The first question to answer with the farmer is why are you planning to do tillage trials? The design of the trial will depend on the answer. Consider whether there are opportunities to:
reduce erosion problems on the farm where there is steeply sloping land;
get the crop in earlier, closer to the optimum window for the best variety, if tillage and seeding could be done more quickly. Would earlier planting lead to increased yield? Would this be an overall economic benefit to the farm? Work out approximate amounts;
cut back tillage passes without loss in yield thus saving money by reducing fuel and implement wear and operator time on tillage activities. Calculate how much might be saved;
reduce a common problem of soil compaction associated with continuous movement of heavy machinery over the land;
minimize loss of scarce water stored during fallow by tilling and planting in one pass. Would this lead to increased yield by making more water available to the crop in the establishment phase? Estimate how much.
Next you need to consider what problems are likely to arise from any changes in tillage technology and how they might be overcome.
Amongst these might be:
dealing with crop residues;
increases in disease associated with residues and reduced soil disturbance and whether a changed crop sequence might be an option to overcome the problem;
increases in pests until the system reaches an equilibrium between pests and predators;
alternative ways of dealing with weeds and the costs of herbicides and their potential problems. It should always be recognized that any chemicals, though very useful in the short-term, may create problems of herbicide resistance in weeds if herbicide types are not rotated in the longer-term;
establishment problems associated with poorer tilth of seedbeds.
The final issue to think about is that the trial must be long-term, possibly more than three years.
When moving from full tillage to zero-till the micro-flora and fauna take a long time to reestablish themselves and reach equilibrium in a relatively undisturbed soil profile. This duration may discourage the farmer from starting the trial even though the potential benefits of reducing the level of tillage are well understood.
If the farmer considers that the benefits of change outweigh the disadvantages and risks, start to put together a plan that is visionary but cautious in size and resources. Give the farmer a commitment on your time through the study.
Keep proposed areas for the study to a minimum unless the benefits of reducing tillage are very obvious (like steeply sloping land). Allow for large enough plots at least 10 m long for later division into subtreatments, for things that unfold as obvious limitations on the farm as the study progresses (see the plot and subplot diagrams in the chapter on What is the best cropping sequence for the farm? sequences a field layout and general methods to useand read there how to layout plots).
Address only the issues raised in the above and associated questions. Restrict proposed measurements in the first two years to establishing that yield does not decline with the changed methodologies. However, if yield does seriously decline in the first year, modify the trial to include subtreatments to determine why. If the reason is obvious and insurmountable, consider curtailing the study at that time.
General aims of the trial
The trial compares three systems of tillage initially for their effects on yield. The longer-term aim, once the systems have been through an establishment phase or preliminary testing for two to four years is to define a tillage management package for the farm and region. This might include proposals for crop sequences, time of planting of specific varieties, weed and disease control strategies and plans for handling of residues.
There is no doubt that to produce an optimized system several other variables will need to be changed when the tillage method is changed.
Choice of tillage systems for the trial
The multi pass conventional system used in the trial should be that normally used on the farm or in the area.
A minimum tillage system should disturb the soil sufficiently in terms of the cultivated width and depth of each row, to give some weed control and an appropriate tilth for seedling emergence. This disturbance should be in one pass concomitant with seeding. A light cultivation may be needed between seasons to control weeds or incorporate stubble. You will need to discuss with the farmer which implements already in use on-farm will be appropriate.
The no-till treatment will be largely dependent on herbicides for weed control so soil disturbance should be that required to open a slot just wide enough for seed and fertilizer placement. This may be only a few millimetres wide. Check on photos in this chapter for ideas on what machinery might suit the farmers requirements or how current machinery might be modified. Choice of herbicide and timing of application(s) will vary with location. The aim should be to minimize applications yet achieve sufficient control of weeds to avoid curtailing wheat seedling emergence and early growth.
Spatial design of the study
A strip design
In the simplest design the three tillage treatments selected for study can be sown as strips next to each other, conventional (C), minimum (M) and zero-till (Z), each one or two seeder widths wide and more than 30 m long. The strips can then be marked out as plots each at least 10 m long to serve as three replicates.
A simple layout for a tillage experiment with three replicates within the farmers crop. The conventional tillage strip is part of the farmers crop. The minimum and zero till strips are added within the crop
If the plots are within a field that is cultivated and sown using the farmers normal procedures, the C strip can be part of the larger crop (see Figure showing a simple layout for a tillage experiment). Choose a part of the farm for the trial where the tillage treatments are most likely to give a benefit. Remember that the location of plots is to be a fixture for at least three years.
If you have identified other issues that should be examined from the outset (options for how to control weeds; options for handling stubble such as burning, incorporation or leaving on the surface; variations on when to sow the crop, etc.) then make the nine plots bigger than 10 m long and split each one to include the important subtreatment (see the example for how to do this in the chapter on optimizing crop sequences). You may not need to include the subtreatment on all tillage treatments, but always include it within all replicates of the particular tillage treatment.
If you are planning to have two sowing dates, then mark out the plots two seeder widths wide and plant the first seeder width as the first date. Plant the second date next to it. Plant in the direction of the arrows in the layout figure in a continuous run from replicate 1 through replicate 3.
If the crops will be harvested by machine, each subtreatment (subplot) may need to be up to 10 mlong. If harvests will be by hand, the subplots could be as short as 2 m.
Measuring rainfall infiltration
If the farm has erosion problems, you may decide to include measurements of rainfall run off in the second or later years of the study. Infiltration is the difference between rainfall measured in a rain gauge and rain measured as run off from the tillage treatment. Erosion is assessed as the degree of turbidity of the run off water (how much sediment it contains). These measurements are made with homemade infiltrometers placed within one replicate of each tillage treatment. You may decide to add a fourth replicate plot for the infiltrometers, three per tillage treatment. The plot need only include the main treatments.
Building an infiltrometer and how it works
An infiltrometer is a means of collecting and measuring the run off. It is a watertight wall enclosing a measured area of the field, but the wall has one leakage hole at its lowest point. Any water that does not filter down into the soil will temporarily collect on the surface within this enclosure and run out of the hole. The escaping water is caught in a pipe and collected at a lower point in a measuring container, usually a drum.
Infiltrometer walls can be made out of anything that will not absorb water and can be any shape. Galvanized steel sheeting 1 mm thick by 200 mm wide is suitable. Three 2.4 metre lengths bolted together with small overlaps will provide a circular four square metre infiltrometer area. Ahole is required in the steel wall to fit a 25 mm diameter or larger drainage hose. Either you or the farmer should have little difficulty making such infiltrometers.
After construction the circular infiltrometer wall is positioned in its plot on the soil surface and pushed vertically into the soil until the drainage outlet is level with the soil surface.
The runoff flows under gravity into a container in a trench, one container per infiltrometer. The volume of runoff is measured after each runoff-producing rain if possible. Percentage runoff can then be calculated by subtracting the collected amount from rainfall measured in a rain gauge located on-site. A60 litre container will collect 15 mm runoff from a four square metre infiltrometer (1 mm of rain falling on 1m2 is 1litre).
You may decide to put your containers in trenches dug in the paths separating the zero and minimum tillage plots and minimum and conventional tillage plots (white strips in the layout diagram).
The amount of sediment in the runoff can be used to approximate erosion by measuring turbidity of the runoff water by eye. First make a visual or descriptive scale of water clarity from 1 to 4. Each time volume measurements are made score each run-off sample after agitating it. Record the scores. A pattern will become apparent over time.
Infiltrometer rings inserted immediately after sowing can be temporarily removed at harvest if necessary then replaced until immediately before sowing the following seasons crop, in order to record infiltration amounts during any out-of-season rains. The crop inside the infiltrometer must be treated exactly the same as the crop in the remainder of the plot.
Measuring the runoff from infiltrometers. The grey galvanized iron walls of six infiltrometers enclose the remaining stubble of a zero-till wheat crop. Drums storing runoff are in a trench so they are slightly lower than the infiltrometer walls
Observing and measuring the crop
Observations of the crop should show which tillage system produces the best economic yield (allowing for costs of inputs) and the most sustainable yield as well as explaining or at least indicating why. Check the introductory chapters for how to collect, measure and analyse plant samples and determine yield. Those chapters also gives a guide to measuring crop water use and water use efficiency.
Rainfall and infiltration data. These data are from the third year of a study after multiple, minimum and no-till treatments began. No-till used a double disc seeder opener at sowing such as pictured earlier. Minimum tillage used full cut-out tine points 50 mm deep, 3-pass cultivation used wide tine points 80 mm deep. Rainfall is the full height of each histogram. Sowing and anthesis dates are marked.
At seedling and spike emergence: counts of seedlings during the two weeks after sowing show whether the method of seedbed preparation limited early growth while counts of spikes at first spike emergence indicate the degree to which later vegetative growth was constrained. Greater water infiltration would be likely to increase spike numbers and potential grain production.
Counts of seedlings and spikes can be made on metre lengths of row that are selected and marked at sowing. These row lengths should be within the crop, that is, bordered on all sides by plants of the same tillage treatment. Two such lengths within each replicate plot are sufficient. While these are quick and easy measurements that can be taken in an hour or two they can be a useful guide to explaining yield differences between treatments. So if possible, collect the numbers with the farmer, find the average and then discuss them.
If soil pathogens or nematodes are likely to be a factor amplified by the main treatments, their occurrence should be estimated. Check with your research colleagues as to how this might be done.
At maturity: grain yield and associated kernel weight are essential measures. Biomass measured at maturity allows harvest index to be calculated (a useful estimate of crop efficiency).
Measures at final harvest should be based on crop samples of at least 1 m2 area cut to soil level. The 1 m2 sample areas should be surrounded by non-harvested border rows. It is essential to measure the area of crop sampled in each plot. In infiltrometer plots the whole enclosed 4 m2 area should be harvested.
If the farm has suitable machinery, preferably harvest the whole subplots minus border and end rows by machine (see companion chapters). The area harvested must be measured. Also harvest the whole infiltrometer plots by machine.
Weeds: a major difference between the tillage treatments may be weed production, particularly if there is no prior experience on-farm with the use of weedicides in reduced tillage situations. Rough estimates of weed effects can be made by estimating the proportion of ground covered by weeds at first tillering. Crop yield losses will approximate percentage weed cover. Make these estimates on each subplot separately and write down the numbers. Discuss them with the farmer.
A better though more demanding way to estimate yield loss due to weeds is to cut a known area (1 m2) of each plot to soil level at spike emergence and dry then weigh the weeds and the crop separately. Yield without weeds would have been actual grain yield increased by the proportion of biomass produced by weeds. Weeds germinating after spike emergence have little negative effect on crop production. For future decisions about types of weedicides to use, it is worthwhile identifying the major species of weeds in the biomass samples. Check the chapter on crop establishment for detailed methods.
It is probably unnecessary to make a detailed assessment of how components of crop yield are changed by the tillage treatments. However, if eyeball assessments indicate there are trends, and you want to analyse them, follow the approaches for harvesting and making calculations in the introductory chapters.
Using the crop measurements
Seedling emergence: until the systems stabilize there may be no benefits seen from the reduced tillage systems. You may decide to make only cursory observations during the first two years after the treatments are commenced.
Once your detailed study begins, take the counts of seedlings emerged from each of the treatments and graph them separately against time from sowing following the methods described in the chapter on crop establishment.
These counts and curves will show in which treatments seedlings emerged first and what proportion of sowed seeds actually became established seedlings.
In a well-established no-till system, seedlings may emerge slightly earlier and tiller more strongly than under full cultivation. This is because under a no-till system less of the soil water stored over the off-season is lost to evaporation so more water may be available for early growth. Furthermore, weed weight rain tends to 100 X concentrate in the crop weight seeding slots rather than dissipating over the whole width of the seedbed and thus soaks more quickly to the developing seedlings. Earlier emergence can lead to greater yield in short-duration crops.
However, on the contrary, seedlings may emerge less quickly through mulch, as the soil surface tends to be cooler. So where no-till is associated with heavy mulch, emergence may be late and tillering and potential yield curtailed.
If you have used three or more replicates, compare tillage treatments within each block separately after comparing performance averaged for the whole trial. Each replicate should give a similar ranking for the tillage treatments. If that is not the case, the effects are possibly due to random variation. Nevertheless, try hard with the farmer to link differences between replicates to observations you and the farmer have made and the measurements you have to hand. There are always reasons for different behaviour.
Spike numbers: compare the data of spike numbers similarly. Do the tillage treatments rank the same across blocks? Do the rankings for spike numbers match those for seedling emergence with early emergence equating with more spikes? Do your estimates of weed infestation link to the numbers of spikes?
If a biomass harvest has been taken at this stage, dry and weigh the crop and weed fractions separately for each plot. Add the numbers for the two fractions together to work out biomass per plot. Calculate the percentage potential crop losses due to weeds by
Multiplying actual yield at the final harvest by that percentage figure approximates yield losses due to weeds. This enables the farmer to work out crop losses in money terms and to equate that loss with the cost of herbicide or labour to reduce the weed problem.
The final harvest: this is the one that matters most to the farmer. If grain yield per m2 is well down on the no-till plots compared with his conventional cultivation, and money has been spent on herbicides, the trial may seem a failure. Though the savings in fuel and time in doing less tillage will have to be factored into the gross returns analysis to assess the degree of economic failure or success.
First, if different areas of crop have been harvested in different plots, convert all the results to a metre square basis or to t/ha. Does ranking of cultivation systems for grain yield remain constant across blocks? Can any differences in ranking across blocks be linked with earlier measured differences in weed infestations, poor emergence or low tiller numbers in specific plots?
Are the differences in yield between treatments so small that they are really insignificant? Can it be concluded that tillage system has no effect on yield? Try throughout to explain why things happened so you can find ways to fix the problem later.
If total crop dry weight (grain, straw and trash) was measured for each plot at harvest, work out harvest index (HI) as grain divided by total. A very good crop should have a value of about 0.5 i.e. 50 percent of the crops above-ground weight should be grain. If the reduced tillage treatments were collecting and storing rainwater better than the conventional tillage system, particularly late in growth, harvest index will be higher. If early growth was excessive and water ran out for grain filling, HI could fall to 30percent or less.
Check average kernel weight in the different treatments by taking a handful of grain from each plot then counting and weighing 100 kernels. If any weights are much below 3 g, the treatment was short of water during grain filling. Rank the tillage treatments in each block separately. Are the rankings consistent or differences absent?
Rainfall and infiltration data
Data from the study described under Measuring rainfall infiltration are used here to indicate how your infiltration numbers might appear. Depending on your soil type and previous use of the land, differences between treatments may not appear until the third year of the study or even later.
Once the soils under the minimal or no-till systems stabilize you would expect to see more infiltration and less runoff and erosion occurring than under multi-pass tillage. This occurred in the histograms of the figure. The red bars showing infiltration (the difference between rainfall and runoff) for the no-till treatment are taller than the blue bars for multi-pass cultivation.
Is there any indication in your data that greater infiltration leads to better growth and yield?
However, when the soil profiles become saturated, runoff from all three treatments should be similar. Equally, if there are high-intensity rainfall events, differences will be small or even absent.
Check to see whether the infiltrometer data from your study are similar. Also check your measurements of turbidity. If the runoff water was always clear from all tillage treatments there are no problems. If the water was consistently more turbid from the multi-pass system you have an erosion problem that should be fixed. Does zero- tillage fix the problem?
The trial does have the major drawback that it must be continued over several seasons if it is going to give a definitive answer about which tillage system is right for the farm or for the site on-farm where it is tested. In some soils and environments it may be five years before soil flora and fauna stabilize under minimum and no-till systems.
It may be most efficient on effort when doing this study to establish the different tillage systems and make only cursory observations and measurements of the crops in the first year.
In the second year, place the infiltrometers and make only learning measurements on them. Save detailed observations for the third or later years. The farm will have to gain experience during the first year on how or whether weeds can be controlled by chemical means (no-till) or by limited till (minimal tillage plots).
Similarly there will be a learning curve for how to manage residues. Is it possible to drill through residues of the previous crop? Should residues alternatively be removed, windrowed, burnt or incorporated. Are they a source of disease?
If the area is dry for most of the season, residues are less likely to be a disease source than if it is wet. If left on the surface, residues will act as a mulch to keep soil surface temperature down and conserve moisture.
While this is likely to be beneficial in hotter regions, in cool areas it may delay crop emergence and development too much with negative consequences to yield. If it is a warm and wet decaying surface, residues can tie up nitrogen and result in the crop looking nitrogen deficient. Incorporated residues act differently to surface residues.
The interactions between residues and weather are numerous and it is not possible to give blanket suggestions for how they should be handled. An approach must be refined for the region.
A common conclusion is that they are more trouble than they are worth, so they should be burnt. This is a simple but wasteful and polluting solution. Furthermore, if retained they can reduce or prevent erosion caused by heavy rain. In areas with sloping cropland this could be important. For example, erosion can be stopped on 15 percent slopes if the surface is covered by straw (about 4tha-1 is needed) and the soil moderately permeable to water. When using any level of tillage on slopes it is always wise to work along the contours.
If weeds emerge before the crop, they will rapidly dominate the use of light, water and nutrients and crop yield will be small. During the early years of establishing a no-till system, it will probably be essential to control aggressive established weeds with herbicides. It may take as long as five seasons of spraying before the soil seed bank of weeds with long dormancy is completely cleared.
Annuals with little dormancy are soon cleared as long as those weeds do not surround the cropped area. Some grass weeds that can regenerate from vegetative fragments can be best cleared by herbicides or by an initial deep ploughing. Shallow normal tillage done poorly can exacerbate the problem.
The positive side of no-till is that once the seed bank of weeds is at a low level, weeds can be controlled by limited chemical applications or by occasional minimal tillage.
The benefit of measuring runoff water from plots is that it provides information throughout on that very important aspect of sustainable farming, erosion control. Even before the minimum or no-till systems stabilize, the trial will allow decisions to be made about the level of danger in the present system. Is erosion a problem over the whole farm or of no consequence? And are the sloping areas of the farm under threat of washing away?
The major advantages of minimum or no-till systems, speed of land preparation and timeliness of crop turn around and sowing, and the reduced costs of tillage, are aspects that should be considered when deciding on a tillage system for the farm.
A mix of no-till, minimum till and conventional cultivation will spread the tillage workload through time. By selecting crop varieties of varying duration matched to the systems, farm production could be optimized in hand with increased sustainability.
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