Enhancing Efficacy of Pea Inoculants on Acid Soils with Molybdenum Background The micronutrient molybdenum (Mo) is critical in the formation of nodules for some legumes. This micronutrient is normally available in adequate amounts in fertile agricultural soils. However, it may not be available to the rhizobia if the soil is acidic. Some research done with soybeans in the southern United States found a yield response to adding Mo to the inoculants in acid soils. There was also an increase in nodulation. The North Peace Applied Research Association (NPARA) at Manning, Alberta has done small plot trials in recent years on acid soils (pH 6.3) having Mo at undetectable level (<1 ppm). NPARA used 0.15, 0.3 and 0.4 ounces Mo per acre and found impressive increases in nodulation using the 0.15 oz. rate. The increase in nodulation on peas inoculated with rhizobia and Mo was much higher compared with peas inoculated with rhizobia alone. The Mo added to the inoculants has a low cost ($2) per acre. It thus appears useful to further explore the potential for increasing pea production and profit margin using Mo with inoculants. Objectives • To provide evidence whether Mo use might increase pea production. • To compare a peat based inoculant (from Novozyme) with molybdenum included, with Soil Implant granular inoculant with sodium molybdate added at time of seeding. • To show in tours and meetings that Alberta Pulse Growers are working on topics of economic importance to growers. Methodology The treatment of Soil Implant granular inoculants with and without sodium molybdate and an experimental peat inoculants with Mo provided by Novozyme were compared. The following two field trials were conducted. Falher 2008: The plots were laid out south of Falher (NW16-77-21-W5), in a randomized complete block design with three treatments (Table 1) and four replications. Soil at the site was Gray Wooded with pH of 6.0. Each plot was 100 feet long by 12 feet wide (the width of the Conservapak seeder). Cutlass peas were seeded on May 30th, for a targeted plant population of 99 plants per square metre (9.2 per sq. ft.). Seeding had been delayed because of rain. Two weeks after seeding the farmer who had RR canola next to the trial sprayed 0.5 L/ac of glyphosate, which took out 60 feet of the 100 feet length. The plots therefore became 40 feet in length. The smaller plot area may have affected the reliability of the results. The crop was straight combined by a Wintersteiger plot combine on August 25th.

Sexsmith 2007: Bob McCreight suggested the field selected for the trial, because he has several years of soil tests that show the pH to be 5.9 to 6.0. The location of the field was next to Bob’s house and yard. The inoculants used for both treatments was Soil Implant granular. The sodium molybdate was in liquid form and was mixed very evenly with the inoculants in an electric cement mixer at a rate that would give 0.3 ounces per acre (8.5 grams) for the 8 lbs per acre of inoculants. This was done immediately before seeding. The cost of the Mo as sodium molybdate works out to approximately $2.00 per acre. Carneval peas were seeded with a Morris Contour air drill on May 15th. Using GPS guidance alternate strips of 48 feet were seeded with the Mo treatment, and the strips without Mo were seeded immediately afterwards. The treatments thus had four replications, each one half mile long. Strips of ½ mile using 25 ft header on a Lexion 560 combine were harvested on Aug 26th ’08. Results Falher 2008: Due to soil conditions at seeding the Conservapak seeder left a rough field finish but the plant stand was good (Picture 1). The peas emerged well on all treatments after seeding. Moisture conditions were good until the end of June, but July brought hot sunny days and drying winds and the crop was not able to meet early promise (seed weather data section). The granular + Mo and peat inoculants with Mo treatments had a statistically significant yield increase of 22.5% and 23.8% compared to the granular inoculants without Mo, respectively (Table 1). There was not a significant difference between yields from the two inoculants with molybdenum. The site was toured during the annual SARDA tour July 31st when 35 people saw the trial. There is interest in the topic but farmers are waiting for more definite results. Table 1. Pea yield for the treatments at the Falher and Sexsmith sites. Falher 2008 Sexsmith 2007 Treatment Yield, kg/ha Yield, bu/ac Yield, kg/ha Yield, bu/ac Granular Inoculants 1707 25.4 1741 29.0 Granular Inoculants + Mo 2191 31.1 1600 26.7 Peat based Inoculants with 2114 31.4 Mo LSD (5%) 2113.6* 4.07* 64.7** 1.08** CV, % 6.1 6.1 1.7 1.7 * and ** refer to significant treatment effects at 5% and 1% probability, respectively. Sexsmith: The seeding conditions were good with adequate soil moisture and the initial crop stand was excellent (Picture 2). The growing season was very stressful with very little rain in June and July and the peas remained short (12-14 inches high). The first significant rain came near the harvest time, in late August.

Roots were dug up at flowering and nodulation was fairly good. The soil was like concrete because of the drought and differences between treatments were not evident. With the crop growing in sub-optimal conditions, it is likely that the crop response to micronutrients was limited. Moisture content of peas was 14%. There was significant difference between the treatments (Table 1). On average the strips with Mo yielded 8% less than strips with no Mo. This result is puzzling and does not agree with the single strip trial that was done in the area last year, or with the trial done at the Falher site in 2008. The idea to have farmers visit the site was abandoned because of the severe drought in the area (three other extension tours were cancelled in the west Peace). Conclusions Considering the contradictory results from the two present sites and the results from earlier studies more work needs to be done before any conclusions can be drawn.

Picture 1. Cutlass peas after 13 days of seeding in trial near Falher.

Picture 2. A good stand of Carneval peas in early June at McCreight’s. Acknowledgements Nick Underwood – Reduced Tillage Linkages