Less tillage means slower breakdown of crop residues, such as straw and chaff, as well as soil organic matter.
Nitrogen contained in crop residue is tied up for a longer time in a direct seeding system and is less available to plants. If the field pea crop is properly inoculated, however, this should not pose a problem.
Spring banding is the most efficient method of applying fertilizer – banding fertilizer in a pea crop is better than broadcasting, since less fertilizer will be available for weed growth, especially if the fertilizer is placed close to the seed.
Never sacrifice seed placement for fertilizer placement – proper seeding depth and soil-to-seed contact is critical.
In heavy clay soils, seed and fertilizer separation may be reduced due to soil lumping.
High seeding speeds may affect seed and fertilizer separation by collapsing the banding trenches.
Too much seed-placed fertilizer can hurt crop emergence, cause severe crop damage and/or increased days to maturity.
Studies on seed-placed phosphorus using double disc openers suggest a maximum of 30 lb./acre of P2 O5.
Soil moisture conditions, row width and width of spread, soil texture and fertilizer type dictate what rate of fertilizer can be safely placed with the seed (higher moisture levels allow for more seed-placed fertilizer),
Row width and width of spread of the seeding tool determines the Seedbed Utilization (SBU) or how fertilizer is scattered in relation to the seed – wider row spacings lead to reduced seedling emergence and yield loss (the same holds true for narrow spread patterns).
The higher the percentage of Seedbed Utilization (SBU), the more fertilizer may be placed with the seed.
Understanding the fertilizer requirements of field pea is critical to reaching optimum yields. To achieve 50 bushels of pea seed per acre, pea crops (including vines and pods) will require approximately:
150 lb. (N) nitrogen
45 lb. (P) phosphate as P2O5
140 lb. (K) potash as K2O
13 lb. (S) sulphur
over 100 lb. (Ca) calcium
15 lb. (Mg) magnesium.
Field pea has the ability to fix nitrogen from the air. The process works like this:
The field pea forms a symbiotic relationship with specific bacteria, which live in association with plant roots.
The bacteria infect the plant roots and form nodules.
The bacteria use nutrients from the plant and provide nitrogen to the plant in return.
For this reason, most of the nitrogen required by pea can be provided from the soil and fixation. This can greatly reduce and often eliminate the need to add N fertilizer. Inoculation with the proper strain of rhizobium bacteria is essential to ensure fixation.
Soil tests are also important in deciding whether or not N fertilizer should be applied:
Generally, if soil tests are above 40 lb. N/ac. in the 0 inch to 24 inch depth, no additional N fertilizer is required.
In soils testing less than 20 lb. N/ac., a small amount of starter N may be beneficial.
In a cold/wet or hot/dry spring, when nodules are slow to develop, plants may be unable to obtain sufficient N from the soil, resulting in a nitrogen deficiency.
When the 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), any additional nitrogen will delay the onset of nodules and reduce nodulation and nitrogen fixation.
Combined soil and fertilizer nitrogen levels greater than 55 kg/ha (50 lb/ac) can prevent nodulation and nitrogen fixation.
It can take three to four weeks after planting before nodules are fully functional. Early plant growth may be poor in soils with nitrogen levels less than 11 kg/ha (10 lb/ac), and plants may appear yellow prior to the onset of active nitrogen fixation due to a nitrogen deficiency. This early deficiency can be corrected by adding low levels (10 to 15 kg/ha, 9 to 13 lb/ac) 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.
Monoammonium phosphate (ex. 12-51-0) can provide a small amount of starter nitrogen needed for early plant growth.
With pea and nitrogen, it’s possible to have too much of a good thing. Excess N fertilizer will reduce the amount of N fixed by a pea crop, delay crop maturity, increase disease levels and reduce standability.
Mid-season N applications are normally not recommended. An exception would be under conditions of failed inoculation and obvious N deficiency.
Adequate levels of phosphorus are critical for optimum yield and early maturity. Phosphorus deficiency restricts top and root growth, resulting in spindly stems with fewer branches.
Phosphorus promotes the development of extensive root systems and vigorous seedlings. Encouraging vigorous root growth is an important step in promoting good nodule development, nitrogen fixation, and early more uniform maturity.
Phosphorus moves poorly in soil, so it should be placed near the seed. On the other hand, germination and emergence can be reduced if too much phosphate is placed with the seed.
Field pea research in Alberta has found that up to 30 lb./ac. seed-placed P2O5 has not reduced germination or emergence – in fact, under very good seedbed soil moisture conditions, even higher rates of seed-placed phosphate are safe.
Peas have a relatively high requirement for phosphorus. A 50 bushel per acre (bu/ac) pea crop takes up 40 to 54 kg/ha (36 to 48 lb/ac) of phosphate and 35 to 43 kg/ha (31 to 38 lb/ac) is removed from the field with the seed.
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.
Even if seed yield increases are not achieved every year, a pea 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 17 kg/ha (15 lb/ac) in a 2.5 cm (1 in) spread and 15 to 18 cm (6 to 7 in) row spacing under good to excellent moisture conditions.
Rates of seed-placed phosphate should be reduced if the seedbed has less than ideal moisture conditions. 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, banding the fertilizer away from the seed (sideband or to the side and below) should be considered. If sidebanding, sideband all the phosphate fertilizer, especially when using narrow openers.
Pea crops generally need more potassium than cereal crops and often almost as much potassium as they do nitrogen. Only 20% to 25% of the plant potassium is in the seed, however, the rest is in the leaves and stems and is normally returned to the soil.
Many Alberta soils are medium to high in exchangeable potassium, often ranging from 400 to 1,000 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.
Potassium fertilizer is not required when soil tests show greater than 300 lb. potassium/acre.
Banding or seed-placing potassium are the most efficient methods of application.
Because large amounts of seed-placed potassium with pea crops may reduce germination and emergence, it may be best to either band it before seeding or sideband it at the time of seeding (this is especially true if phosphorus and sulphur fertilizers are also being applied).
Peas have a high demand for potassium at about 135 to 165 kg/ha (123 to 150 lb/ac) K2O for a 50 bu/ac crop. This works out to just over 1 kg/ha (0.9 lb/ac) for every bushel of grain produced. Use a soil test to determine whether additional potassium is required.
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 of phosphate mentioned previously (17 kg/ha or 15 lb/ac). Most of the potassium taken up remains in plant residue and is not removed with the grain.
Pea crops have a reasonably high sulphur requirement. Much of the topsoil sulphur is contained in soil organic matter. This is slowly released as sulphate-sulphur (SO4-S), the form of sulphur that plants require. Sulphate-sulphur is similar to nitrate-nitrogen in that both are mobile in soil.
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.
For testing purposes, soil samples should be taken from the 0–6 inch, 6–12 inch and 12–24 inch depths to determine the amounts of sulphur at each depth.
A 40 bu/ac pea crop requires about the same amount of sulphur as a 40 bu/ac wheat crop, approximately 9 to 11 kg/ha (8 to 10 lb/ac).
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.
If sulphur is required, apply a sulphate containing fertilizer such as ammonium sulphate (21-0-0-24).
Elemental sulphur fertilizer won’t be available to the plant in the year it is applied – elemental sulphur is best used in a longer term program to build soil sulphur levels.
Micronutrient deficiencies for pea production have not been identified as a widespread problem through pea growing areas of Western Canada.
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.
To achieve a 50-bushel yield of pea, the micronutrients needed are:
0.06 lb. (B) boron
0.09 lb. (Cu) copper
0.63 lb. (Fe) iron
0.45 lb. (Mn) manganese
0.09 lb. (Zn) zinc
trace amounts of (Mo) molybdenum
field pea can tolerate what is considered low or deficient Cu, Zn or B levels.
impact of micronutrients on other crops
Note that pea 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