I attended the Agvise 2011 Canadian Soil Fertility Seminar in Carman last week. There were a lot of really impressive speakers there. Here are a few of my notes on what was covered.
Nutrient Trends – Using the Data. John Heard
John Heard led off by letting us know that Better Crops Magazine has recent nutrient trends.
Currently nitrogen removal in Manitoba is very close to nitrogen fertilizer applied. He also showed some long-term trends – currently nitrogen addition and removal is roughly in balance. Farmers applied more nitrogen in the 90s than they removed in crops. Prior to that farmers removed more nitrogen with the crops than what was added as fertilizer. Two factors that aren’t accounted for in this are that manure adds about 7-8% to the total nitrogen supply and pulses and forages also fix nitrogen.
Phosphate has a similar trend – currently net exporting P2O5. Manure adds about 15% to phosphorus supply. We’ve been removing K2O from soils for years and are still drawing it down at rates of roughly 4 removal to 1 add.
Fertilizer prices spiked in 2008 – but are currently close to normal levels.
Soil testing has gone up a lot in recent years (about 5.2 million soil tests in US in 2010). In Manitoba, soil samples have roughly tripled in the last 10 years: 2001: 14,999, 2005: 36,155, 2010 42,392. Almost 40% of Manitoba samples are coming from zone/grid managed fields. Soil test results on hay fields are biased because most hay fields aren’t sampled. They’re mostly only sampled for manure management. It’s likely that the current upward trend in phosphorus is due to manured fields rather than fertilizer application. Soil test K levels have increased 10 ppm in MB in the last 10 years, again probably due to manure application.
Tracking Soil Nutrient Levels for Your Clients. John Heard
Nutrient removals are exceeding nutrient application. On a short-term basis low analysis starters can work, but you’re going to need make up the removed phosphorus somewhere! When growers are costing fertilizer, they should look at the purchasing power per bushel. It’s not the cost of the fertilizer; it’s how much fertilizer you can buy with a bushel!
Phosphorus and the 4Rs. Rigas Karamanos
Probability of wheat response to application of phosphorus as a function of soil test P: <5 ppm 100% response, 6-10 71%, 11-20 ppm 50%, 21+ 25%. The response to phosphorus for peas is similar to that for wheat.
Soil chemistry and precipitation play a huge role in the behavior of phosphorus in the soil. If soil test phosphorus numbers are not correlated to the yield, they mean nothing (soil tests show potentially available, not necessarily what the crop can actually get to). There are tests to show available (soluble) phosphorus but they will give very small numbers because available phosphorus is a tiny part of the soil’s phosphorous pool. Pop-up effect is a temporary increase in solubility
It takes about 10-20 days for plants to get to soil phosphorus (no roots), then there’s a huge uptake, and then it slows down.
What determines maximum crop yield? Genetics (each crop has a genetic max), solar radiation (tends to be constant), water (variable), nutrients (somewhat controllable)
Rules of thumb:
- If it’s too good to be true, it probably is.
- Beware of hype – hype hurts.
- Don’t trust testimonials because they are anecdotes not data.
- What did the opposing side say?
- Ultimate standard: is there published peer review evidence.
- There is no substitute for thinking critically and thinking for yourself.
- At the end it is YOUR decision!
Polyphosphate fertilizer is very similar to orthophosphate. Polyphosphate converts to orthophosphate very quickly in a day or two. Unless you’re applying the phosphorus after seeding, by the time the plant takes up the phosphorus from the fertilizer all the fertilizer products have the same extractable P. No difference between products.
When midrow banding be careful as the high concentrations of nitrogen can keep the plant from reaching the P. You can end up with large hot bands where nitrogen needs to migrate out before phosphorus is accessible. Shallow banding is better than deep banding (12-year study)! Seed row placement is generally a bad idea (reduced yield in 8 out of 12 years). When the field is tilled, in row is better, when direct seeded mid-row is better (30 year study). Why? Don’t know.
Liquid fertilizer has spacing issues just like dry fertilizer – it comes out as droplets not a steady stream!
Some phosphorus is required for maintenance as well as crop needs. Extensive leaching of phosphorus and K is expected on soils with a pH less than 4.5. However long-term movement and stratification is possible (largely through erosion). Phosphorus uptake is not significantly different under different tillage systems
Once Around the Nitrogen Cycle. Les Henry
He spoke about how grossly contaminated wells have to be before things such as blue baby start to be a problem. In almost all cases the problem comes from wells and not from aquifers. It is possible that it’s the bacteria and not the nitrogen directly that was responsible for blue baby.
The efficiency of the mineralized nitrogen is probably 100% – now we need a better measure of mineralization. Mineralization rate doubles for every 10 degree rise from 5-35 C. Moisture: On a % basis mineralization and moisture content linear between WP and field capacity. Les has a simple nitrogen Mineralization Test – take sample in fall, place moist soil in loosely tied plastic bag and leave sit at room temperature for 4 weeks, dry and analyze as normal. This only works if soil is at field capacity to soil test depth.
Project Smorgasbord. John Heard.
John Heard told us a bit about Ray Bittner’s P Ramp Calibration strips in the Interlake area. More phosphorus = More Alfalfa – less phosphorus = more bare patches. If alfalfa feed tests < 0.2% phosphorus there is phosphorus deficiency in the soil. Increasing phosphorus increases protein content (vs. check). John emphasized how easy it is to set up a ramp calibration strip – it takes roughly 18 minutes/plot.
He also gave us a quick report on damage affecting ESN. John noted that there is lots of damage to ESN during application. A simple test for checking amount of damage is to take ESN that’s come out of your fertilizer applicator: add water to 3g ESN, weigh it, and wait about 24h. Weigh again. What’s dissolved is lost. Minnesota and Alberta reported averages of 24% and 13% damage, with more damageat the end of booms and at higher air flows. This damage to the ESN coating didn’t reduce crop yield.
The Manitoba test showed less damage than in other regions
Residual Soil nitrogen Levels as a Yield Sufficiency Tool? Rule of thumb is that less than 30 lbs. residual nitrogen indicates under fertilized crop. However there is no research cited. Initial research shows if residual nitrogen >60, then more nitrogen than needed was applied. However, underfertilized and optimally fertilized left roughly same amounts of residual N.
Wheat Grain Nutrient Content. Tom Jensen.
Tom Jensen gave us results for an experiment trying to show a relationship between soil test nutrient level and grain nutrient levels. The hypothesis is that soil content will affect grain content. The results didn’t show this for most nutrients: negative correlation for N, some correlation for P and K, good correlation for Boron, no good correlation for Cl, Fe was significant correlation, there were no Cu deficient sites, so no good test, not a good correlation for Mn, and Zn has the best correlation between soil test and grain. This needs more research!
Effect of Nitrogen Fertilizer Source and Management on Grain Yield and N2O Emissions. Don Flaten.
N2O is a very powerful greenhouse gas. Agriculture is about 9% of Canada’s greenhouse gas emissions. In Manitoba agriculture is about 1/3 of greenhouse gas emissions.
A lot of N2O is released when soils thaw. There are concerns with fall spreading because of late fall / early spring losses. Denitrification doesn’t contribute much to N2O if it’s too wet or too dry. Research so far shows no significant effect of nitrogen source or timing on N2O emissions at Winnipeg and Brandon 2001-2003. N2O emissions are highly variable by site, year, and so on. Don suspects nitrification is responsible for most emissions, but can’t prove it yet. Two main emission processes – Denitrification, Nitrification
As far as grain yield goes, there is no convincing evidence showing any agronomic penalties for fall application vs. spring.
A few key events that might only be a few days long seem to account for most of the emissions
Despite the lack of evidence, greenhouse gases from agriculture will attract lots of attention in Manitoba in the next few years.
Crop Scene Investigation. John Lee
Analyzing Plant Tissue results is tricky.
When collecting samples:
- Store or ship immediately
- Never test plant roots!
- Don’t ship soil
- Fill out information completely
- Bags need holes to prevent rotting/mold
- Be sure to include enough plant material
Sufficiency ranges are established for almost all crops and nutrients. A second test, DRIS is available for some crops. DRIS -20 to +20 is considered normal, lower than -20 is deficiency. It is very helpful to pair tissue tests with soil tests taken at the sites where tissue was collected. Plant analysis can sometimes show us what’s limiting and the degree of the limitation. Plan tissue analysis works better when combined with a site specific soil test and visual data.
