Garth Butcher, Birtle, Manitoba

In 1998 I applied inputs sufficient for a 40 bushels (2,000 lb.) per acre canola crop in our area, but the yield I realized was only 15 bushels (750 lb.) per acre. This was extremely disappointing, my worst crop, relatively speaking, since I began zero tillage farming twenty years ago. The yield loss was mainly due to severe spring frost.

I have been very low keyed about the long term effects of zero tillage on my soils, but repeated frost events in late May/early June of 1998 followed by excessive rainfall for the following two weeks convinced me that my soils had changed more than I previously thought.

I had 600 acres of canola that was planted between May 8^th and May 14^th. At the time of the first frost, May 28, 2,000 acres had been sprayed with post emergent herbicides, 200 acres were not yet fully emerged, and 200 acres were in-between those two stages of development. Between May 28^th and June 4^th there were three more frosts and general cold conditions.

All of the canola experienced extreme frost damage, more severe than neighbouring conventional fields, but also significantly worse than some nearby zero tillage farmers who use fairly similar management practices but who have not been practicing zero tillage for as long a period of time. As well, some land that I had just began to farm had significantly less frost damage than my long term zero tillage fields even though the same methods were being used.

I have been aware of the increased susceptibility to frost of zero tillage crops for a long time. On several occasions over the past twenty years my crops, particularly canola, have sustained more frost damage than conventional fields nearby. These crops also recovered to a large extent, although with some thinning particularly in trashier areas. This was exaggerated in earlier years when the frost was more severe in chaff rows where chaff spreading was less adequate. I never experienced a yield disadvantage because the improved moisture availability became a more important factor later in the growing season. In fact, in most cases I felt I had a yield advantage despite the frost.

I feel the increased susceptibility to frost in zero tillage crops comes from several factors. This effect is amplified when dealing with susceptible crops such as canola and when a field has been in zero tillage for a longer period of time.

The most important effect is the insulation that the trash on the surface provides. Less heat is radiated from the soil and therefore temperatures drop lower around susceptible plants. This also reflects the suns energy instead of absorbing it. The soil below is somewhat cooler which means there is less heat to radiate up around the plants at night. As well, warm up in the morning after a frost is slower in such a situation. It would also follow that cool down the evening before would happen sooner with less energy absorption as the sun sets.

This is not the only effect going on though. The soil layer below this trash layer is different in a zero tillage environment. Sometimes referred to as the duff layer, it has a lower bulk density, a lower specific heat, and is more insulating than a conventionally tilled soil. There is less heat to radiate, and radiation is more restricted than on tilled soil. This same effect can be seen on "breaking" where frost damage is more severe as compared to land that has been farmed for a longer time, even when there is no trash in either situation.

Even having taken these factors into account, why did I experience such a huge yield loss in 1998 as compared with frost damage in previous years? The most important factor was probably the severity of the frost. Lower temperatures and four below freezing nights on a short period of time amplified the susceptibility of my zero tillage crops. In the past, the typical frost was a one-time event that allowed damaged plants to recover. My zero tillage soils are more "mature" now and therefore are more susceptible, relatively speaking. As well, due to a good crop the previous year, my average residue levels were high. The excessively wet and cool weather that followed further worsened the situation.

Underdeveloped and later seeded crops in the area did not fair as well as more advanced crops when the rains began, and all of my canola was under developed at the time due to the frost damage. As well, when it started to rain, my zero tillage fields were at higher moisture levels and came to the saturation point more quickly, causing further problems.

As you can see, I have done a lot of analyzing and agonizing because of the frost of 1998. Having gone through that process, what will I change in 1999?

Thankfully my memory of my 1998 canola crop is fading, and I have and will be making only minor modifications in my program. These changes will include:

1. Try to avoid two high residue crops in a row. My most severely damaged field

had been barley in 1996 and winter wheat in 1997.

2. When we applied NH3, this past fall we banded a little deeper to achieve a

somewhat darker surface and to mix residue into the soil a little more. This may reduce the duff layer.

3. We will harrow the land that was fall banded to mix soil and residue and speed

up residue breakdown; again to reduce the duff layer. This practice also seals up banded land from moisture loss in the spring.

4. We will continue using a hoe drill with on-row packing. Concern with frost was

The ideal seed row would be a trench with all residue removed with all the residue between the rows. As you know, the hoe drill doesn’t work perfectly in this way.

It is important to have a perspective on the frost some of us experienced last year. For me, it was a one in twenty year event and perhaps more like a once in fifty year event for a frost period that severe. If global warming is occurring then the risk should be reduced. As well, in considering what I have described, realize that I farm in the most frost susceptible area in all of Manitoba due to a combination of elevation, latitude, and location. I am going to be careful not to throw the baby out with the bath water when considering a change in my system.