Inoculation and Fertility
Chickpeas have the ability to fix 60-80 per cent of their nitrogen requirements through nitrogen fixation. Kabuli chickpeas are excellent nodulators and nitrogen-fixers. Desi chickpeas are good nitrogen-fixers under ideal conditions, but may be a little sensitive to adverse environmental conditions.
Chickpeas require a specific Rhizobium species for nitrogen fixation (Rhizobia cicero), and it is different from Rhizobium used for peas and lentils. Examine the label of any inoculant to make sure that it is appropriate for chickpeas. Some chickpea inoculants will be labelled as “garbanzo bean,” and are appropriate for use in chickpeas. 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 temperature extremes, drying out, or direct sunlight. Inoculant must be stored in a cool, dark 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 tank mix inoculant with 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 adverse environments and seed-applied fungicides than other forms of inoculants.
Inoculants are available in different formulations: liquid, peat-based, 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.
Research completed at the University of Saskatchewan evaluated the performance of inoculant formulations in chickpeas. Results indicated that inoculation using granular formulations was as good as, or better than other formulations. The peat-based 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 to ensure sufficient numbers of the correct strain of highly effective rhizobia is available. Inoculant is economical relative to its potential benefits. The risk of poor nodulation is too great to not inoculate each time the crop is seeded.
The effectiveness of inoculation can be checked by examining the crop at early flowering. It may take up to four weeks after seed germination before nodulation reaches a point where it can be evaluated. 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 a nodulation failure is noted by early summer, nitrogen can be applied as a rescue treatment. Check at early flowering, seven to 10 days (approximately the 8 node stage). 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 (39 to 49 lbs/ac) should be made.
This nitrogen is best applied as broadcast urea or dribble banded liquid 28-0-0. The use of a urease inhibitor, such as 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 to decrease losses.
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.
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 can enhance 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, provided adequate levels of phosphorus fertility are present to begin with.
Fertility requirements for chickpeas are not well-defined. Based on limited data, the requirements for phosphorus, potassium, and sulphur are similar to peas or lentils. A well-inoculated crop should not require nitrogen fertilizer, provided the appropriate Rhizobium inoculants are used and 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 seedbed), chickpeas may benefit from low rates of starter nitrogen in some years. 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, including seeding into standing stubble prior to May 15, 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 chickpeas 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 suggest 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.
Phosphorus: Chickpeas have 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. Chickpeas remove approximately 0.36 lb P205 per bushel of seed.
Chickpeas 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 lbs/ac.
Potassium: Potassium is usually not required as a fertilizer supplement in most soils where chickpeas are grown. When soil test levels are very low, a small amount should be seed-placed. However, seed-placing potassium may cause seedling damage. The maximum safe rate of potassium and phosphorus is 20 lbs/ac (22 kg/ha).
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 consistently identified as a problem through chickpea growing areas of Western Canada, although no research has been conducted to access micronutrient requirements of chickpeas. 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.