The interest in pulse crops in the southwest has been steadily increasing over the past few years. In addition to choices of varieties, there is now a larger choice of inoculants to use. A lot of excitement has been generated over granular inoculant. Granular inoculant differs from the other two seed coated formulations in that it is applied to the soil in the seed row, not unlike you would apply fertilizer in a single shoot system. There are certain advantages to using granular inoculant, such as ease of use and metering. The rhizobia in granular inoculant also has greater protection from desiccation relative to the peat powder or liquid type, allowing granular inoculant to survive for extended periods in the soil. In most cases, seed applied inoculant results in nodules that are clustered around the seed or crown of the plant. Since granular inoculant is in the soil, nodules tend to form on the lateral roots. This generally results in more nodulation on the lateral roots and nodulation that encompasses much more of the shallow root zone. Previous studies have indicated that in many cases, there was also a yield increase with the use of granular inoculant.
Under the Special Crop Sector of the Agri-Food Innovation Fund, seven Applied Research and Demonstration Farms across Saskatchewan initiated a study to look at the interactions between seed applied fungicide and inoculant formulations in Carneval peas under zero tillage. Inoculant treatments consisted of an uninoculated control, a liquid, and a granular formulation. The fungicide treatments included a control, Apron, and Apron plus Thiram. Emergence, nodulation, harvest dry matter, thousand kernel weight, percent protein and yield were examined. This experiment was conducted on land that had no history of pulses grown on it to best evaluate crop response without any residual effect from past applications of inoculant.
There is only one year's data so far in this study, so conclusions are very premature at this stage. There have been very variable results over the seven locations, which is not too surprising, this being the first year of the 5 year study. For the purpose of this article, I will be focusing on the Swift Current site managed by Wheatland Conservation Area. At Swift Current, there was an interaction in 1997 between fungicide treatment and inoculant formulation.
I was surprised at how well the untreated/uninoculated treatment yielded (Figure 1). Some of this response may be explained by the position of the slope these plots may have been located on, providing better moisture (the site has gently rolling topography). However, it is more likely a result of sufficient nitrogen available in the soil in combination with some starter nitrogen that was applied at time of seeding. There were excellent soil moisture reserves in the spring and timely precipitation occurred during the growing season. The yield for this control treatment will not likely remain as proportionately high in relation to the other treatments over time, especially in drier years. The nodulation and plant vigour for the control was much lower than the granular treatment and somewhat lower than the untreated liquid inoculated treatment (Figures 1 and 2). However, the nodulation was higher than expected overall, indicating there was sufficient native rhizobia present in the soil at these plot locations to cause active nodulation.
With respect to yield, when no fungicide was applied, there was no difference between the granular inoculant treatment and the control (untreated/uninoculated). The untreated liquid inoculant treatment, although the highest yielding of the liquid treatments, was nearly 200 lbs/ac lower than the control (Figure 1). The granular treatments all showed an increase in yield and nodulation response compared to the treatments having liquid inoculant. When fungicides were added, the granular treatments again showed the best response in yield and nodulation. In addition, when the treatments were rated on the basis of vigour, the granular treatments all produced higher plant vigour ratings (Figure 2).
The Apron/Thiram/Granular treatment had a significant yield increase over the control and was 325 lbs/ac above the best treatments with liquid inoculant (Figure 1). However, this same fungicide treatment had a very negative impact on yield and nodulation scores when liquid inoculant was used. This effect was also observed at Indian Head, Canora and Redvers. Since there wasn't a Thiram treatment alone with any inoculant treatment, it is difficult to determine if the negative response to the liquid inoculant is a result of Thiram itself or a combined effect with Apron. The Apron/uninoculated treatment resulted in the lowest yields compared to the Apron/Thiram/uninoculated treatment or even the Apron/Thiram/liquid treatment. This effect was also observed at Melfort, and Indian Head.
There was a response to protein to inoculant formulation at Redvers and Scott (data not shown). At both locations, there was an increase in percentage protein with granular inoculant showing a higher increase in protein than the liquid formulation. At Swift Current, there was no significant difference between inoculant treatments. However, there was an interaction with the Apron/Thiram/liquid inoculant formulation resulting in a significant decrease in percent protein in the seed relative to the control or granular inoculant formulation. There was no significant difference in protein between the inoculant formulations without fungicide, the control, or with Apron.
In summary, this first year of results have provided variable
results over the seven locations of this study. However,
indications suggest there are positive responses of pea yields to
granular inoculant without fungicide treatments or with either
Apron or Apron plus Thiram. When Apron was applied without
inoculant, there was often a reduction in yield. The combination
of Thiram and Apron had a very negative effect on yield and
protein when applied with liquid inoculant, however, the
Apron/liquid inoculant treatment did not have a negative effect
on yield. As more years of data are compiled, some of the
variability may be sorted out. I understand that treatments with
Thiram only on the two inoculants and uninoculated treatments
will be included in 1998 to see whether Thiram itself is not
compatible with liquid inoculant or if it is the combination of
Thiram and Apron that may be the problem. Although granular
inoculant is more expensive than liquid inoculant, initial
evidence suggests that in many areas of the province, such as the
drier areas, granular inoculant can provide advantages in yield
and convenience.
Figure 1: Carneval pea yields and nodulation scores, 1997
Swift Current.
Figure 2: Nodulation and plant vigour scores, 1997 Swift Current.