- Understanding the fertilizer requirements of lentil is critical to reaching optimum yields. The crop will respond to added fertilizer nutrients when soil test levels are low to medium. It is always best to soil test as an aid in developing a sound fertilizer management program.
- Lentils can derive up to 80% of its nitrogen requirements through nitrogen fixation. The remaining nitrogen comes from the soil (available at time of seeding plus mineralized during growing season).
- As the supply of nitrogen from soil and fertilizer increases, the amount of nitrogen fixed by the plant decreases.
- Nitrogen is necessary for high yields, but generally nitrogen fertilizer application is not required for lentil.
- N starvation may occur during and immediately following emergence. Lentil plants begin root nodule formation about two weeks after plant emergence. During this period, plants may turn pale green, called the “period of N starvation,” and it is normal. With proper inoculation, nodules will soon start to function and eliminate this problem.
- Where combined levels of soil and fertilizer nitrogen reach 28 to 40 kilograms per hectare (kg/ha) or 25 to 35 pounds per acre (lb/ac), development of nodules and nitrogen fixation may be delayed. Combined soil and fertilizer nitrogen levels greater than 55 kg/ha (50 lb/ac) can prevent effective nodulation and nitrogen fixation.
- It can take three up to four weeks following planting for nodules to become fully functional.
- Early plant growth may be poor in soils with nitrogen levels less than 11 kg/ha (10 lb/ac), causing plants to appear yellow prior to the onset of active nitrogen fixation due to nitrogen deficiency. This early deficiency can be corrected by adding low levels (10 to 15 kg/ha) of starter nitrogen at seeding.
- Although high levels of starter nitrogen may appear to help the crop overcome a nitrogen deficiency during early crop growth stages, final seed yields may not increase. Typical applications levels of monoammonium phosphate (ex. 12-51-0) often provide the small amount of nitrogen needed for early plant growth and, depending on the soil test, may provide the starter nitrogen required.
- If called for, N should never be seed placed. Instead, applications before seeding (or side-banding where there is separation of the seed and N band) are recommended.
- Yellowing of a lentil crop may also be due to flooding, which deprives roots of needed oxygen (these conditions, if they persist, will also cause inoculant failure). Yellowing may also be a condition of seedling root rot.
- Soils with high N content prior to planting will inhibit nodule formation and are unsuitable for lentil production.
- Mid-season N applications are normally not recommended. An exception would be under conditions of failed inoculation and obvious N deficiency.
- Too much soil N reduces yield by encouraging rank plant growth and delaying maturity.
- Lentils 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 fixing process and in promoting earlier, more uniform maturity.
- Lentils grown on soils testing low in available phosphorus or under cool wet conditions may respond to phosphate fertilizer. However, dramatic yield responses are not always achieved. Even if seed yield increases are not achieved every year, a lentil crop may benefit from improved stress tolerance as a result of phosphorus application.
- The maximum safe rate of actual phosphate applied with the seed is 22 kg/ha (20 lb/ac) with 10% to15% seedbed utilization (SBU) under good to excellent moisture conditions.
- Calculate SBU by dividing seed spread by row spacing. For e.g. a 2.5 cm (1 in) spread with 25.4 cm (10 in) row spacing, equates to 1/10 or 10% SBU. Rates of seed-placed phosphate should be reduced if less than ideal moisture conditions exist.
- Higher rates of phosphate fertilizer placed in the seed row with narrow openers like discs or knives can damage the emerging seedling and reduce the stand.
- If higher phosphate rates are required, band the fertilizer away from the seed (sideband or to the side and below), or increase phosphate levels in the years prior to growing lentils.
- Lentil is moderately tolerant to seed-placed phosphate. Up to 15 lb. of P2O5 per acre may be safely applied with the seed.
- Even though seed yield may not be increased every year in response to phosphorus fertilizer, the crop may still benefit from earlier maturity.
- Research has also shown that although phosphorus is a limiting factor in many Alberta soils, build-up of soil phosphorus tends to raise available soil phosphorus levels and phosphorus fertilizer responses are often not dramatic.
- Lentils have a high demand for potassium.
- Use a soil test to determine whether additional potassium is needed.
- Seed-placing potassium may cause seedling damage. As with phosphate, a wider opener may allow for slightly higher safe seed-placed rates.
- The sum of seed-placed potassium (K2O) plus phosphate fertilizers must not exceed the recommended safe rate of phosphate mentioned previously (22 kg/ha or 20 lb/ac).
- Most of the potassium taken up remains with soil residue and is not removed with the grain.
- Many Alberta soils are medium to high in exchangeable potassium, often ranging from 400 to 1000 lb. of potassium/acre in the 0 inch to 6 inch depth of soil.
- Potassium deficiencies are most likely to occur on sandy soils that are intensively cropped or on Grey-Black transition soils and Grey Wooded soils.
- Sulphur is required in a relatively significant amount.
- A 30 bu/ac lentil crop requires approximately 9 to 11 kg/ha (8 to 10 lb/ac) as lentils remove about 0.2 lb/bu of sulphur.
- Soils testing low in available sulphur should have this deficiency corrected by side-banding, mid-row banding, or broadcasting ammonium sulphate, which contains sulphur in a plant-available form.
- Most research indicates limited yield response from the addition of sulphur fertilizer except in fields testing very low in sulphur.
- Sulphur is normally not limited in most irrigated soil as irrigation water contains substantial amounts of sulfate-sulphur (amounts in the water vary over time) – approximately 30 lb./ac. of sulfate/sulphur is added to the soil with 12 inches of irrigation water.
- Some soils are deficient in plant-available sulphur in the topsoil but have enough sulphur in the subsoil to meet crop requirements.
- In wetter, cooler conditions, plants may suffer from a lack of sulphur before plant roots grow down into the subsoil containing sulphur.
- Sulphur deficiencies are frequently a problem in the Black and Grey Wooded soil areas of Alberta and occasionally a problem in the Brown and Dark Brown soil areas.
- Test soil to a depth of 24 inches to determine if sulphur fertilizer is required – if analysis levels are less than 20 lb./ac., follow recommendations of the analysis report.
- Micronutrient deficiencies for lentil production have not been identified as a widespread problem through lentil growing areas of Western Canada.
- Micronutrients namely boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) and zinc (Zn) are usually adequately supplied by most soil types.
- 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.
impact of micronutrients on other crops
- Note that lentil is not grown continuously on the same land – other rotation crops such as flax, wheat, canola and barley may respond optimally to the topped up levels of these minerals:
- The three remaining micro-nutrients – iron, manganese and molybdenum – have a much more critical effect.
- Most Alberta soils are adequate for iron but high pH soils or alkaline soils may lock up manganese availability so that a foliar application of this micronutrient may be necessary.
- Molybdenum becomes much less available in acidic soils (below pH 6.5) especially at pH 5.5 or less.
- Molybdenum is absolutely essential in the nitrogen fixation process in legumes – without it, no nitrogen can be fixed (in Europe, producers may apply 200 to 300 grams of actual molybdenum to the seed crop or soil every few years or lime the soil to bring up the pH and release more molybdenum).
- Based on soil test results, micro-nutrient fertilizer should be applied in test strips the first year. Sandy, low organic matter may show best response.
- For more information, recommended soil micronutrient levels are tabulated in the fact sheet: Minerals for Plants, Animals and Man, Agdex 531-3 and Micronutrient Requirements of Crops, Agdex 531-1.