Liquid Rhizobial Inoculants for Lentil and Field Pea

Abstract

Traditional peat legume inoculants are viewed by western Canadian farmers as being difficult to apply. A liquid inoculant was developed and its feasibility as a carrier for Rhizobium legurninosarum bv vicieae strains 99A1 and 128C56G for lentil ( Lens culinuris Medik.) and pea ( Pisum sutivum L.), respectively, was examined. The population of the strains exceeded 33.8 × 10 6 /oz (10 8 /mL) for 9 mo when held at 41°F and stored in a warehouse with temperatures between 41 and 70 °F. One and 8 mo‐old inoculant stored as previously described nodulated their host crop. Studies using commercial scale farm equipment determined that the liquid inoculant gave a very uniform coverage of the seeds when applied through a grain auger and that the inoculated seeds flowed well when planted using various types of seeding equipment. Pea producer trials in Saskatchewan showed that the liquid inoculant was much easier to apply than the peat inoculant and that the yield of field pea was similar with either inoculant. Research plot field trials in Saskatchewan and Alberta showed that the liquid inoculant for pea and lentil resulted in yields equal to or better than those observed for the peat inoculant and that proper inoculation gave yield increases of lentil cv Laird and field pea cv Radley and Express of 546 (29%) and 303 (9%) Ib/acre, respectively over the uninoculated control. Research Question Field pea and lentil producers in western Canada inoculate their seed with Rhizobium as it is augered from storage bins to seeding equipment. Seed is treated with one of several sticking agents followed by application of the peat to the moistened seed. The objective of this study was to evaluate a liquid carrier of Rhizobium for field pea and lentil. Does the liquid formulation maintain an active and large population of Rhizobium ? Would a liquid inoculant equal the yield performance of the peat inoculant? Literature Summary Proper inoculation of legume seed can provide a large and effective population of Rhizobium . For several decades farmers have relied on peat as a carrier of rhizobia and, while it is an excellent medium for sustaining a large microbial population, it can be messy and time consuming. A typical western Canadian farm operation seeding 200 acres of field pea will have to inoculate 16 tons of seed. Therefore, it was not surprising that these producers requested a user friendly inoculant. A liquid formulation had been developed for the soybean rhizobia, Bradyrhizobium japonicum . We adapted this technology as a means of meeting the request of pea and lentil producers in western Canada. Study Description Shelf Life —This study examined the shelf life of two strains of Rhizobium leguminsarum bv viceae , 128C56G and 99A1, effective on field pea and lentil, respectively. The strains were packaged into plastic bags with capacities of 12.7 fluid oz (the traditional soybean liquid inoculant size) and 1.06 gal, proposed for the western Canadian market. The viable count of the strains of Rhizobium in the liquid formulation was determined periodically over 8 mo by removing samples, serial diluting the samples, and planting them onto a suitable growth medium. Seed Survival —Field pea and lentil seed were treated with 1 and 8 mo old liquid inoculum and seeded within 1 h of treatment or stored at 70°F and seeded at 24 and 48 h after seed treatment. Nodules per tap root were counted after growing in the greenhouse for 5 wk. Field Studies—In 1991, nine pea producers compared the ease of use and grain yield following treatment of seed with the peat or the liquid inoculum on 40 acre plots. In 1991–1992, we used replicated research plots (8.2 by 20 ft) in field pea and lentil fields to compare N 2 fixation (C 2 H 2 reduction) and grain yield following treatment with the peat or the liquid inoculum. Applied Questions Does a liquid formulation of Rhizobium maintain a shelf life sufficient for the planting season for field pea and lentil producers? Populations of both strains of Rhizobium exceeded 337.8 × 10 6 colony forming units (cfu)/oz (10 9 /mL) at the time of packaging and after 8 mo storage at 41 to 70 °F. The number of nodules that developed on field pea and lentil seed treated with 1 and 8 mo‐old inoculum was not significantly different ( P = 0.05). The liquid inoculum meets the Fertilizers Act of Canada (1988) requirement that large seed legume inoculants supply 100 000 viable, crop‐specific rhizobia per inoculated seed to ensure adequate nodulation, N2 fixation, and yield. Will the liquid inoculant perform as well as the peat inoculant? The mean yield of field pea treated with the liquid and peat inoculum from the producers trials did not differ at 2041 and 2021 lb/acre, respectively. The grain yield of field pea and lentil from the research plot also showed that the liquid inoculant performed as well as the peat inoculant (Tables and ). Inoculation of lentil and field pea with strains 99A1 and 128C56G, respectively, resulted in average yield increases of 564 (29%) and 303 (9%) lb/acre over the uninoculated treatment. Recommendation Inoculation of field pea and lentil with Rhizobium ensures that a large and effective population is available to colonize, develop root nodules, and fix N 2 for the crop. The peat‐based inoculants remain as excellent carriers of Rhizobium . However, the liquid inoculant described is user friendly and performed as well as the peat inoculant. Effect of inoculant formulation on yield of lentil inoculated with Rhizobium leguminosarum bv vicieae 99A1 in Saskatchewan research trials. Raymore Rosetown Moose Jaw Success Sovereign Treatment 1991 1992 1991 1992 1991 1991 1992 1991 Mean ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ lb/acre ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ Liquid 1134 1724 1941 1960 2403 2426 906 2784 1910 Peat 1088 1921 1711 2116 2126 2297 1177 2925 1920 Uninoculated 782 848 1223 913 1991 1820 586 2788 1369 LSD ( P = 0.05) 303 667 230 452 387 318 368 NS NS Effect of inoculant formulation on yield of pea inoculated with Rhizobium leguminosarum bv vkieae 128C56G in Saskatchewan and Alberta research trials. Redwater Pigeon Lake Saskatoon Treatment 1991 1992 1991 1991 Mean ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ lb/acre ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ Liquid 3908 3700 2558 3361 3382 Peat 3875 3443</jats

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