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Fine Tune Fertilizer Rates By Field, Not By Crop

The goal of a crop fertility plan is to determine the fertilizer rate needed to hit the yield target while accounting for nutrients already present in the soil. But farmers may wonder why it is important to spend time calculating different fertilizer product rates. Why not just use the same fertilizer blend across the whole farm or have a wheat blend and a canola blend?

Putting a little extra time and effort into a fertility plan can improve crop growth, reduce environmental impacts and, perhaps most importantly, produce a greater financial return.

The basic steps to building a fertility plan are: decide on crop rotation; set achievable yield targets; list nutrient uptake and removal rates; measure available nutrients in the soil; and, finally, calculate the amount of fertilizer necessary to make up the difference. Farmers should also understand the purpose of the fertilizer components when determining application rates and proportions.

Once you ve settled on a rotation plan, determine the yield potential of the field by looking at historical data and averaging yields over the last three or four times that crop was grown. A good rule of thumb for targeting higher yields is adding 20 per cent to the average.


Different farmers have different approaches on fertilizer recommendations, usually depending on their specific circumstances. Whether the land is owned or rented makes a difference, as does the term of the lease. Short-term lease land may just get enough nutrients for the crop the sufficiency approach. Land that is owned is treated more with a building program and is a long-term investment. I use the information from The Canadian Fertilizer Institute ( uptake and removal chart, which shows the amount of nutrients that a crop requires to grow and how much of the nutrients are removed when it s harvested. There are a range of values on the uptake and removal chart the growing season and geography of your farm determines where you fit on the scale.


A good fertilizer program requires reliable and representative soil-sample results, so take time to evaluate every part of your soil sampling technique. Samples sent to the lab must be collected in a way that maintains the integrity and validity of the sample. If you re hiring out the job, hire trained operators who collect samples consistently with the proper equipment.

A big part of a soil sample analysis report is an analysis of the changes in nutrient levels compared to previous soil sample information, so always take samples from the same areas to compare the changes in those areas. Record sample points and benchmark for baseline information. You can use GPS co-ordinates to get back to the same place or measure sample points from a reference point near the field, such as a fence post or survey marker.

Take samples at the same depth each time. Most soil scientists recommend two samples, one from between zero and six inches and the other between six and 24 inches. Keep the samples pure and be very careful to not contaminate them with other soil or dust. Use a clean plastic pail and rubber gloves when mixing soil to break up lumps. Label sample bags and fill out field information sheets accurately with all of the required information. And be consistent when labelling samples. For example, don t change the names of fields each time you sample them. It is imperative to do the best job possible when taking soil samples in the field to get the best information from the lab on the analysis.

Pick a soil sample lab that reports information in an easy-to- understand format and stick with that lab in order to get more consistent reports.


One way to think about soil is to view each field like a bank account FINE TUNE FERTILIZER RATES BY FIELD, NOT BY CROP

only one containing nutrients instead of money. This bank account of nutrients has deposits (the main one being application of fertilizer prior to crop establishment) and withdrawals (the main one being the harvesting of the crop). There are other important withdrawals and deposits taking place throughout the year in the field fertility bank account these are akin to service charges that draw down your balance or interest that adds to the level of available nutrients. Withdrawals for nitrogen include leaching, denitrification, volatilization, and erosion. The interest on the fertility bank account can be additional nitrogen from legume residue, other plant and animal residues and mineralization of soil organic matter.

It s important to confirm the fertility bank account balance in the field and understand what the regular deposits and withdrawals are. Confirm your soil fertility bank account balance compared to where you think it should be.

Another way to look at nitrogen is as the fuel in the tank to get you where you want to go. If you only got partway to where you wanted to go, chances are there s some unused fuel left. If you got a little bit farther than what the plan was, you probably drove on the reserve part of the tank for a little while or got better mileage than expected. Look at the other nutrients as the oil in the engine and the air in the tires. Maintain proper levels from start to finish and everything will run pretty smooth. If those levels start to drop too low, you can have a major problem and when they run right out, it is usually a bigger issue to fix them.


When planning to increase rates of nitrogen, also look at increasing rates of other nutrients proportionately. Expect to see greater yield response from an increase across the board than just bumping up nitrogen. When increasing primary nutrient rates, you also have to look at the micronutrients required for high-end yields. Crops have different response rates to certain micronutrients and it is important to make sure that they are not lacking.

The chances of success are much greater when you have the end goal in mind. Farmers will see agronomic benefits of crop fertility planning by following the straightforward process of determining yield targets, reviewing uptake and removal rates, soil sampling and calculating application requirements.

Practically speaking, the intensity of a crop fertility plan is limited by application equipment and in-season logistics. Look for ways in the current system to improve the fertility plan. Check application records for how much fertilizer was applied on each field, account for the crop removal with accurate yield information, and check that the soil sample report shows a reasonable balance.




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