Inoculation and Fertility
Chickpea has the ability to fix 60 to 80 per cent of its nitrogen requirement through nitrogen fixation. Kabuli chickpea is an excellent nodulator and nitrogen fixer. Desi chickpea is a good nitrogen fixer under ideal conditions, but may be a little sensitive to adverse environmental conditions.
Chickpea requires a specific rhizobium species for nitrogen fixation. Chickpea rhizobium species are not the same as the rhizobium species for peas and lentil. Examine the label of any inoculant to make sure that it is appropriate for chickpea. Some chickpea inoculants will be labelled as “garbanzo bean,” and are appropriate for use in chickpea. Note that many different strains of this rhizobium species occur and vary in terms of their effectiveness. The manufacturer may have one or more strains in the inoculant.
Nitrogen fixation is a symbiotic relationship. Rhizobium enters the root hairs of the plant and induces nodule formation. The plant provides energy for the rhizobium, and the rhizobium in return converts atmospheric nitrogen from the soil air surrounding the roots into a form that can be used by the plant. Maximum benefit is derived if the supply of available soil nitrogen is low and the soil moisture and temperature levels are adequate for normal seedling development from the time of seeding until seedlings are well established.
Rhizobium bacteria (either on the seed or in the package) die if they are exposed to stress such as high temperature, drying winds, or direct sunlight. Inoculant must be stored in a cool place prior to use and must be used before the expiry date. Following application of the inoculant, plant the inoculated seed into moist soil as soon as possible.
Inoculants are sensitive to granular fertilizer. Banding fertilizer to the side and/or below the seed is recommended. Never mix inoculant with granular fertilizer. Inoculants are also sensitive to some seed-applied fungicides. Check the label of both the inoculant and seed treatment for compatibility. When using a combination of fungicide and inoculant, apply the fungicide to the seed first, allow it to dry, and apply the inoculant immediately prior to seeding. Granular inoculants are less affected by dry seedbeds and seed-applied fungicides than other forms of inoculants.
Inoculants are available in different formulations: liquid, powder, and granular. All inoculant formulations will perform equally well if the inoculant is properly applied and if environmental conditions are ideal. Under adverse conditions the best performing formulation should be granular, followed by peat, and then liquid.
The effectiveness of inoculation can be checked by examining the pulse crop in early summer at early flowering. It may take three to four weeks after seed germination before nodulation reaches a point where it can be evaluated. Although chickpea is an excellent nitrogen fixer and the nodules can be easily seen when a plant is pulled from the ground, the best way to check for nodulation is to dig a plant and gently remove the soil from the roots by washing in a bucket of water. Nodules are fragile and readily pull off if the roots are pulled out of the soil.
If the rhizobia are actively fixing nitrogen, the nodules will appear visibly red or pink inside. Nitrogen fixation is synchronized with plant growth, supplying the crop nitrogen during rapid vegetative growth.
Seed applied inoculant should result in nodules forming on the primary root near the crown. If the inoculant was soil applied (granular), nodules should be found on primary and secondary roots. If nitrogen fixation is active, the nodules will be pink or red on the inside. Lack of nodules indicates rhizobia did not infect the pulse plant. Lack of a pink colour (usually green or cream coloured) indicates the rhizobia are not fixing nitrogen. Nitrogen fixation declines once plants begin pod formation and seed development.
Research completed at the University of Saskatchewan evaluated the performance of inoculant formulations in chickpea. Results indicated that inoculation using granular formulations was as good as, or better than other formulations. The peat-based powder and liquid formulations performed as well as the granular formulation in some instances, especially when soil moisture was not limited. Studies carried out in drier soil conditions favoured granular products.
Chickpea crops should be inoculated each time they are grown. This ensures sufficient numbers of the correct strain of highly effective rhizobia are available where they are needed. Inoculant is economical relative to its potential benefits and nitrogen fertilizer replacement. The risk of poor nodulation is too great to not inoculate each time the crop is seeded.
Pulse inoculants and pre-inoculated seed products are supplements, as defined by the Fertilizers Act, and are subject to registration and monitoring for quality control.
Inoculation for Phosphorus Solubility (for all pulse crops)
JumpStart® contains the fungus Penicillium bilaii and is also available in the dual inoculant TagTeam®. This fungal inoculant enhances phosphorus solubility and uptake by plants. The fungus colonizes along the root system of the plant, and through the production of organic acids, increases the solubility of soil or fertilizer phosphorus. Keep in mind that JumpStart® will normally replace approximately 11 kg/ha (10 lb/ac) of P2O5.
Fertility requirements for chickpea are not well-defined. Based on limited data, the requirements for phosphorus, potassium and sulphur are similar to pea or lentil. A well-inoculated crop should not require nitrogen fertilizer, provided the appropriate Rhizobium inoculants are used and nitrogen fixation is optimized. If nitrogen fixation is not optimized due to unfavourable growing conditions (e.g. relatively dry seed bed), chickpea may benefit from low rates of starter nitrogen in some years.
Generally, nitrogen fertilizer is not required if nitrogen fixation is optimized. Well-nodulated chickpea plants can derive 50 to 80 per cent of their nitrogen requirement through fixation under favorable growing conditions. If nitrogen fixation is not optimized due to unfavourable growing conditions (e.g. relatively dry seed bed), chickpea may benefit from low rates of starter nitrogen in some years. But, Saskatchewan research conducted with four chickpea varieties from 2004 to 2006 showed no differences in seed yield when sown with or without starter nitrogen when granular inoculant was utilized.
Most chickpea varieties are late maturing. Management of maturity is critical to optimize crop quality. In addition to field selection and seeding practices to encourage early crop development, nitrogen fertilization management can be used to manage maturity. Research conducted in Saskatchewan concluded that cropping strategies and practices that produce vigorous early growth allow for earlier pod set. This early pod set ties up plant resources and minimizes the production of new podding sites. A strong early pod setup provides a strong reproductive sink and helps slow the production of new vegetative tissue. The results showed that nitrogen fertilizer supplied to non-inoculated chickpea accomplished many of these strategies.
Starter nitrogen (N) of 28 to 56 kg N/ha (25 to 50 lb N/ac), without inoculant, resulted in earlier maturity by an average of 13 days in normal to cooler/wet seasons. In dry years, only marginal differences were noted as drought conditions accelerated crop maturity. Research at Swift Current and Shaunavon, SK suggests the best practice may be to apply starter nitrogen instead of inoculating the seed. Earlier research using starter-nitrogen for maturity management utilized higher starter-nitrogen rates of 56 to 67 kg N/ha (50 to 60 lb N/ac), applied away from the seed, without inoculants.
If a nodulation failure is noted by early summer, nitrogen can be applied as a rescue treatment. Check closely seven to 10 days prior to flowering. Nodulation and nitrogen fixation should be well developed by the 12 node stage. Although application rates have not been established, an immediate top-dress application of 44 to 55 kg/ha should be made.
This nitrogen is best applied as broadcast urea or dribble banded liquid 28-0-0. The use of Agrotain®, which protects the urea-nitrogen for up to two weeks while waiting for a rain to move the nitrogen into the soil, should be considered with this later application of nitrogen.
Phosphorus: chickpea has a relatively high requirement for phosphorus. Phosphorus promotes the development of extensive root systems and vigorous seedlings. Encouraging vigorous root growth is an important step in promoting good nodule development. Phosphorus also plays an important role in the nitrogen fixation process and in promoting earlier, more uniform maturity. Chickpea removes approximately 0.36 lb P205 per bushel of seed.
Chickpea grown on soils testing low in available phosphorus may respond to phosphate fertilizer even though dramatic yield responses are not always achieved. Even though seed yield may not be increased every year in response to phosphorus fertilizer, the crop may still benefit from earlier maturity.
The maximum safe rate of actual seed placed phosphate is 20 lb/acre.
Potassium: potassium is usually not required as a fertilizer supplement in most soils where chickpea is grown. When soil test levels are very low, at least a small amount should be seed-placed. However, seed-placing potassium may cause seedling damage. The maximum safe rate of potassium and phosphorus is 20lb/ac.
Sulphur: if identified as deficient through a soil test, sulphur can be added by side banding, mid-row banding, or broadcasting ammonium sulphate.
Micronutrients: deficiencies have not been identified as a problem through chickpea growing areas of Western Canada, although no research has been conducted to access micronutrient requirements of chickpea. If a micronutrient deficiency is suspected, it is advisable to analyze soil and plant samples within the suspect area and compare the analysis to soil and plant samples collected from a non-affected area of the same field. If the analysis confirms a micronutrient deficiency at a relatively early growth stage, a foliar application of the appropriate micronutrient fertilizer may correct the problem.