WHAT’S THE VALUE OF YOUR STRAW
with wheat harvest right around the corner, the question of what to do with the straw has made itself top of mind. “It’s always a challenge to come up with one number that demonstrates the value of your straw,” says Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) wheat specialist, Peter Johnson.
“There are a lot of different variables farmers need to consider before they make the decision to bale their straw,” says Johnson. “Straw returns a lot of nutrients to the soil and can be an important source of organic matter.”
Although finding a number that completely encompasses the whole value of straw is impossible, a good place to start is the formula outlined in the OMAFRA Agronomy Guide for Field Crops.
|P& K only Straw value ($/tonne) =
$/tonne MAP x 0.003 +
$/tonne potash x 0.014
|N, P, K Straw value ($/tonne) =
$/tonne urea x 0.015 + $/tonne MAP x 0.003 + $/tonne potash x 0.014
|To change value to cents/pound,
divide answer by 22.05
“This is a good start, but it doesn’t include the value of organic matter or the value of micronutrients,” warns Johnson.
The value of the micronutrients in your straw is dependent on several different factors and is often field specific. “If your field has sufficient micronutrients – meaning you don’t need to buy them – assume they are worth nothing,” says Johnson. “They aren’t actually worth nothing, but there is enough in the soil to last for quite some time and leaving the straw in the field will provide no added benefit from a micronutrient perspective.”
organic matter management
Despite the difficulty in measuring its true benefits, the level of organic matter in the soil is important to consider before making the decision to harvest straw. For soil that is already high in organic matter – for clay soils, that’s six percent organic matter, 4.5 percent for silt soil and three percent for sandy soils – straw can be sold without negatively impacting the field. “But for clay fields with three percent organic matter, you need to be doing everything you can to build up the organic matter and that includes leaving the straw in the field,” says Johnson.
“For every three crops of straw that you sell off of the field, that’s the equivalent of 0.1 percent organic matter,” says Johnson. Although that may seem like a small amount, for a field with only three percent organic matter, 0.1 percent can make a big difference. “That 0.1 percent increase will hold at least one inch more available water. What’s the value of a one inch rain on July 15 during a dry season when corn is tasselling? That’s HUGE!” says Johnson, putting the value of organic matter in perspective.
think about tillage
The final consideration in the straw management debate is tillage. In some cases, leaving the straw in the field can be harmful to the next crop. “If you’re growing no-till corn after wheat, the straw can hamper the ability of the soil to dry and impact planting time,” says Johnson. With the rainy planting season of 2011 fresh in minds, this will be an important consideration for the 2011 harvest.
The other downside of straw in the field is the haven it provides for insects like slugs.
However, if the conditions of your field require more nutrients or organic matter, Johnson recommends managing the straw within the field as opposed to removing it completely to combat these challenges. “Limited tillage in the fall is a good thing,” he says. “It doesn’t take much to deal with the straw: one pass with the disc and the problem is eliminated.”
it starts at the combine
It’s also important to spread the straw uniformly. “If you are running a 40 foot draper head and it’s only spreading the straw 25 feet, something isn’t working,” says Johnson. There is a lot of potash in straw and while you may not be harvesting it from the field, if the straw isn’t properly spread, neither are the nutrients.
“The combine has to be able to spread the straw uniformly over the width that the header cuts. Chaff spreaders are a must and new knives are essential,” says Johnson. “The spreader needs to have the capability to match the header. That is the only way it will work.” •