by David Rourke and Andrew Hargrave

Improvements in seeding equipment with precision placement of seed and fertilizer, improved herbicides, lower cost of Roundup and concerns for moisture conservation have all contributed to the movement toward direct seeding into stubble. What happens to the soil ecosystem in direct seeding and what factors must one consider when choosing a rotation in a one pass system?

Certainly, soil structure will change with the lack of pulverization. Microbial activity will increase. Soil moisture availability and soil moisture holding capacity should also increase. Weed dynamics as well as disease pressures will change. So how can one economically manage these changes? There is no substitute for good management. By monitoring the changes in the field, a good manager can alter farming practices to meet the new obstacles and also take advantage of the benefits of direct seeding. One of the most important considerations is to adjust crop rotations to take advantage of improved soil conditions and also to manage weeds and diseases. One might also add that weeds and diseases which do not exist need not be controlled! Of course, the rotation must be economically sustainable, but at the same time must maintain soil quality and limit weed resistance and disease accumulation.

What are some of the factors which should be considered when choosing a rotation? First, one has to consider the limiting factors in the cropping area such as frost free days, growing degree days and available moisture. 2) the potential yield and market value of that crop, 3) the cost of inputs to grow a crop. 4) Are herbicides available to control your weed problems in a particular crop? 5) What diseases have been appearing in a particular field? 6) Will present seeding and harvesting equipment be adequate for the crop and residue? 7) What are the moisture and nutrient needs for the crop? This is not an exhaustive list, but wilt help to narrow down the choices for a good rotation.

1) Cropping region and soil type:

Growing crop varieties which are compatible to the growing region is important. Frost-free days, growing degree days and available moisture are important considerations A further consideration might be lower soil temperatures in fields with higher residues Seeding into this situation with a low disturbance drill may not provide an adequate microclimate to provide the soil temperature needed for germination and may delay emergence and ultimately shorten the potential growing season (Figure 1). A higher disturbance drill will allow the disturbed area to warm up more quickly, thus minimizing this problem.

Frost -free days and potential growing degree days will be a limiting factor when considering potential crops to insert into a rotation. In shorter growing season areas such as Riding Mountain, it is important to choose more frost resistant crops such as peas or shorter growing season crops such as Polish canola, oats and barley (see Appendix 1). In longer growing season regions such as south central Manitoba, growing season is not generally a limiting factor for crops such as corn, sunflowers and sugar beets.

If soil moisture is a limiting factor, direct seeding becomes more important. Snow trap in stubble over winter becomes much needed soil moisture at seeding. In the Minto, Manitoba area, there was as much as 3 V2" more of available moisture in zero till after wheat compared to conventional till at seeding in the top 4' of soil. Even a fall banding pass will reduce available moisture at seeding. The extra moisture in Zero till allows for shallower seeding and therefore results in quicker emergence and a more vigorous crop. To further provide soil moisture, heavy residue crops such as barley) oats and CPS wheat should be induced in the rotation.

On the other hand, if too much soil moisture is a problem, such as in the Red River valley, more crops with less residue cover should be included in the rotation. Crops such as flax (when baled), peas, canola and lentils when managed properly provide little soil protection, allowing the soil surface to dry in the spring. A further option would be to fall band to remove excess water.

2) Potential yield and market value:

Of course, $ and sense are important when considering crops in a rotation. It is important to have a flexible rotation to be able to take advantage of market trends. Naturally, in regions where crop choices are not as limiting, the options are far greater. Once a list of possible crops to be grown has been established, the next consideration is to maximize the potential return. Look at the market value of the different crops and the potential yield of these crops in your area. This has to be looked at in the longer term as well as the short term. Some land may benefit by the inclusion of alfalfa in the rotation. Although the potential return may not be as high as other options, future crops may benefit in the long run. (Work at the University of Manitoba by Dr. Entz has provided incite for getting in and out of alfalfa without breaking the soil.) On the other hand, if there is no potential market for the alfalfa hay or seed, this option may not be a viable one. In short, a rotation should be chosen which will maintain or enhance yields of future crops and bring an economic cash return in the present.

3) Cost of inputs:

The cost and efficacy of inputs should also be thrown into the economic equation. Seed treatments and innoculants, fertilizer, herbicides, fungicides, insecticides, and even combining, trucking and storage costs should be considered. The decision to use pesticides will be based on an economic decision, i.e. whether the net margin warrants the added costs. If it is anticipated that these pesticides may be needed before a crop decision has been made, this may influence the choice of crop or variety which may be used.

Fertilizer inputs in direct seeding should probably be looked at more closely. Most recommendations are based on conventional till systems. Increased moisture and microbial activity may make it more economical to use higher rates of fertilizer (away from the seed please!). At the CTPC, increasing the nitrogen inputs well above the recommended rate resulted in economic yield increases in most situations. Furthermore, a split application allows for more sensitivity to moisture conditions.

4) Herbicide availability:

Are there herbicides available to handle the antecedent weed population including volunteers? Up until now, the spectrum of weeds controlled in broadleaf crops has been limited. Roundup and Harvest tolerant canola varieties will help to reduce some weed problems at a reasonable cost. The registration of Pursuit in alfalfa and peas will help to control broadleaf weeds which were previously difficult to control.

Further herbicide considerations when deciding on a crop rotation are the need to rotate herbicides and to change timings of applications. This will prevent both the build up of herbicide resistant weeds as well as the development of new weed problems by exclusion of control.

Over the years Zero tillers may have been relying more heavily on Group 1 herbicides for grassy weed control. It appears that Group 3 herbicides (Advance, Edge, Rival, Treflan, Trifluralex, Fortress and Trifluralin) and Group 8 herbicides (Avadex BW, Avenge and Fortress) are an ideal fit in zero till, reducing the potential for Group 1 resistance (Figure 4). Considerable positive data has been developed on surface application Of these herbicides in a zero till system. Rotate herbicides in order to control different problem weeds every year so that a particular weed does not get neglected, creating problems down the road. If a particular weed is a problem and can best be controlled in a particular crop, then using that crop may be necessary to set the weed back enough for other crops in future years. Varying the seeding dates and harvest dates, the use of pre seeding and pre harvest herbicides will help to control different weeds at more vulnerable times.

The use of a very competitive crop like barley periodically in the rotation will help to suppress weeds with minimal or no herbicide inputs.

It is essential to be able to control volunteers from the previous year in a subsequent crop.

5) Diseases:

What diseases have been appearing in a particular field? How many years must a crop be excluded because of root rots, septoria, black leg, sclerotinia, ascochyta, etc.? What can be done to reduce these diseases? Some work has been done by Dr. Cook (Washington St.) and Dr. Bailey (Saskatoon) which has shown that leaving soil undisturbed, may reduce the viability of some disease inoculum. Despite this, it is still advisable to rotate crops. Work at the CTPC has shown that seed treatment and fungicides were more effective in zero till wheat when grown every other year than in successive years. There was a definite economic advantage to reducing the number of years of wheat. There was also evidence that wheat was more responsive to fungicides in a more diverse rotation. It is recommended t at crops susceptible to sclerotinia should be grown once in 4 years. There is work in progress in Minto which is looking at shorter rotations of lentils and peas in zero till. Avoidance of consecutive annual crops and crops with like disease inoculum will help to reduce disease build-up. Choosing disease resistant varieties would also be advisable when a disease inoculum may be present.

6) Seeding equipment:

Some crops such as corn require special seeding equipment. A purchase of new equipment or conversion kit to adapt existing equipment may be required at a cost to include some crops in the rotation. Also, special harvesting equipment may be needed for some crops such as a pick-up for peas to either make harvest possible or more efficient. Seeding into heavy residue may be a problem for some drills. For example, seeding canola into barley stubble at V2 with a ZT disc drill. There may be problems with hairpinning. Another factor may be fertilizer placement. Inherent with direct seeding is the need to precision band fertilizer away from the seed. Seed placed fertilizer is risky especially with crops such as canola and flax. With sensitive crops a better choice may be to broadcast the fertilizer.

7) What are the moisture and nutrient needs of a crop?

It may be an advantage to use a heavy nutrient and moisture user following a less nutrient taxing crop. In the case of a legume crop or perhaps a forage crop such as alfalfa, nitrification may take place for two years allowing for two successive crops of heavy nitrogen users following these crops. Fertilizer inputs should still be used, but perhaps at a reduced rate.

In areas of moisture restrictions, it may be necessary to alternate heavy water users with crops not as demanding. This may be flexible depending on fall and winter moisture.

There is no magic rotation for everyone! To choose the rotation (or rotation options) which is right for you it is important to take into account climatic and soil restrictions, cost of inputs, weed and disease pressures, machinery capabilities, economics and market conditions. Alternating crop types and herbicides is always a good idea where possible. Direct seeding has many potential pitfalls and opportunities. It is up to you to act on them!

Appendix 1. Days to maturity for some crops grown in Manitoba and Saskatchewan Crop Days to Maturity
Barley	60 - 90
Polish Canola	73 - 83
Buckwheat	80 - 90
Yellow Mustard	80 - 90
Oats	85 - 95
Brown Mustard	85-95
Flax	85 - 100
Lentils	85 - 100
Wheat	90 - 100
Field Peas	90 - 100
Navy Beans	90-100
Coriander	90 - 100
Argentine Canola	92 - 102

Black Beans Source: Agricultural Climate of the Eastern Canadian Prairies, 1992.