Western Canadian crop production is all about nitrogen, right? Well, yes and no. Nitrogen is largely the most limiting nutrient for crop production here and is applied in the greatest amounts, yes, but a farmer would be very unwise to under-value a plant’s access to the proper levels of other macro and micronutrients.
That, for the most part, is well understood in cereal and canola production, but when it comes to pulses — a crop that creates its own N as long as it has the proper inoculum applied — there’s also uncertainty surrounding P, K, S and micronutrients.
“Pulses are viewed as if they take care of themselves, and they do to a certain extent, given that they make their own nitrogen,” says Tracy Preete, agri-coach with Agri-Trend Agrology. “But when targeting high yields, the crop needs optimum levels of phosphorus, potassium and other nutrients, too.” What’s more, there is some research to suggest that starter N is still money well spent, especially if growing conditions are poor at seeding and soil nitrogen levels are low.
How much fertilizer do pulses need? Well, that depends. A decent starting point to determine rates is field history. Dale Risula, special crops specialist with the Saskatchewan Ministry of Agriculture, encourages farmers to look at the last crops grown, yields, removal rates of the big-four nutrients and take into account moisture levels and rooting depths of past crops. Pulses are a relatively shallow-rooted crop, making them a good fit after deeper rooting crops like cereals, but it also means that nutrient levels and moisture at lower depths may not be useful to the crop.
Preete understands why farmers typically choose to soil test ahead of cereals or canola because of their appetite for N, but that soil testing carries the same value ahead of pulses, too. Pulses use phosphorus, potassium and sulphur just like any other crop and will yield best when all nutrients are provided in adequate levels, Preete says.
A response to phosphorus fertilizer in ideal growing conditions might be tough to gauge. In a challenging growing season, however, a P application is well worth the money, as access to soil phosphorus is often restricted by cold soil temperatures and slow root development. the plant is more likely to access the close-by, usable form. We’re not talking huge levels of fertilizer here, either. Depending on field history and a soil test, you may only end up adding 20 pounds of P2O5 and maybe 10 or 15 pounds of K2O, but it could have a significant impact on yields. As always, follow seedplaced fertilizer safety guidelines
(see Figure 1).
Many farmers are clueing in and seeing the value of applied P and sometimes K, however adding S isn’t on many radars just yet, and for good reason. A 30 bushel/acre lentil crop uses the same amount of S as a 40 bushel/acre wheat crop, or about eight to 10 pounds of S, says Ken Panchuk, soil specialist with the Saskatchewan Ministry of Agriculture. “If canola is grown in rotation and is fertilized for optimal S levels, there should be enough S cycling through the soil to provide lentils with enough S,” he says. The key is to not let the canola run out of S and to keep tabs on soil levels over time.
If you’re taking the time to do a soil test, Preete suggests collecting as much information as possible, including analysis of micronutrient levels such as zinc and boron. For the most part, micronutrient deficiencies in pulse crops are rare, however, over time, deficiencies are more likely to occur. “Benchmarking where your micros are at gives you a point of reference so you can track what’s happening (to levels),” Preete says. In addition to field records and soil test data, tissue test analysis and visual inspections are other great tools to help predict if levels are sufficient on a field by field basis.
N AT SEEDING?
And what about starter N? Pulse seedlings do need some nitrogen in the early growth period prior to nodule formation; nodules may take three to four weeks to form. In ideal growing conditions, most or all of that needed N will be provided by the N component of most phosphate fertilizers, as long as there’s more than 10 pounds of available N per acre in the first six to 12 inches of soil. In less-than-ideal situations — a cold or overly wet spring or an N deficient soil— farmers and researchers alike have seen a good response to just a bit of N put down at seeding or with the seed.
“For the most part, if you’re applying phosphorus (11-52-0) at recommended rates, you’re likely putting down enough starter N,” says Risula. It’s important to note that a higher seed bed utilization rate (i. e. paired row seeding or side-band application) increases the safety of seed-placed nitrogen.
It should go without saying that pulses should be inoculated with the correct strain of rhizobia bacteria before going in the ground, as each pulse crop needs a specific type of bacteria. It’s also important to remember that it’s not just the right kind of bacteria that makes nodule formation successful — you need a critical number of live bacteria on the seed and seedling for the magic to happen. Risula says that if seeding is delayed after inoculation or if seeding conditions are dry (or cold and wet), it’s definitely good insurance to bump up inoculant rates before the seed goes in the ground.
Seed treatments can affect bacteria survival as can using chlorinated water during the inoculation process. It’s important to factor mortality into the process and bump inoculant rates accordingly, Risula says. And it’s not a bad idea to order your inoculant early to ensure the right type and amount of inoculant is available right when you need it.
Industry guidelines for seedplaced fertilizer and tips on inoculation can be found at www.agriculture.gov.sk.ca/inoculation_ pulse_crops.
MAXIMUM SAFE RATES OF ACTUAL SEED-PLACED PHOSPHATE (P2O5) FERTILIZER. CROP
Canaryseed, pinto bean Flax, pea, forages (alfalfa, bromegrass)
Fababean Lentil, mustard, chickpea