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February 2014 Archive for Ask an Agronomist

RSS By: Farm Journal Agronomists, Farm Journal

Have your agronomic questions answered by a Farm Journal agronomist. E-mail us directly at, and we’ll respond on this blog to provide an interactive dialogue.

Assess the benefit of using management zones versus grids for sampling

Feb 19, 2014

Question: We have done 2.5 acre grid samples the last two years and spread fertilizer with the grids. Can I move out to 10-acre grids and get average and get the same results? We are in the southeast part of Georgia.

Answer: I would not let a grid establish how I pulled the samples.  I would look for any information I can get for how the field yields to start with.  However the field yields is how it should be sampled.  I like to lay soil types down first and then the yield maps and aerial imagery of fields over my soil maps to refine the zones.  I always respect my soil types and then subdivide those soil types down into zones based on water drainage, water availability and crop growth. Instead of looking at 2.5-acre or 10-acre grids, I would look at your yield maps.  If you don’t have yield maps in cotton and peanuts, I would look at aerial imagery (NDVI) as well as thermal imagery to help me define how the field yields. Take the high, medium and low yields in the field – that’s how it should be mapped out and sampled so you have a better picture.  Your yield map and soil test map should correlate. Granted, yield maps in corn are easy to get, while cotton and peanuts may be a lot harder to do. If that’s the case, I would rely on NDVI or thermal imagery to help me have a good map, and then I would sample it by management zones not grids.  A management zone can vary in size.  Some might be 10 acres in size and others as small as 2 acres.  Let soil type, topography, fertility and yield history separate the field out into management zones.  By that I mean, for example, with corn if I have one area making 220 bushel/acre consistently and another area making 150 bushel/acre, those are two separate management zones. If you know how that field yields, that’s how it should be tested.

How to Navigate Zone Management

Every risk has its reward. With zone management, the reward is higher yields and profitability. How to navigate zone management decisions to realize the benefits of variable-rate technology over time.


10 Tips to Help You Safely Enter Zone Management

Chris Barron of Carson and Barron Farms in Rowley, Iowa, has spent the past few months planning and preparing his crew to test the zone management waters


Is it ok to inject chicken manure into fields this time of year?

Feb 11, 2014

Question: What harmful effects might injecting chicken litter into fields this winter have on soil fertility and/or soil structure?

Answer: From a chicken litter standpoint if you’re injecting it now you have to think about what the carbon-nitrogen ratio is in the chicken litter. Straight chicken manure with no bedding will have about a 10-to-1 carbon-nitrogen ratio. That’s not a problem. But if the chicken litter has any bedding with it like wood chips, the carbon ratio could go up and this could create a nitrogen deficit situation for the crop you’re planning to grow. So, in corn for instance, instead of getting a nitrogen return from your manure it could take six months to a year to get the nitrogen out of the manure and that could create a nitrogen deficiency in your corn. From a fertility standpoint what’s the carbon-nitrogen ratio? If it’s 20-to-1 or lower, you probably will have no negative effects from that perspective.  From a soil structure standpoint you have to consider the salt load.  Depending on the soil type, it can hold from 300 to 600 units of salt without too much damage.  But if you’re injecting upwards of 600-plus pounds of salt per acre you could destroy the soil structure.  That’s broadcasting it.  Now, if you took that 600 pound of salt and banded it, you would destroy the structure in the band. You can check your salt index when you run a manure analysis.  If you keep your salt applications typically below 300 pounds per acre you don’t usually have much of a problem. But if you get into levels above that you could destroy the soil structure. Also, in regard to soil structure, the timing of application matters if you have to deal with the results of wheel track compaction. In terms of a carbon penalty, the more time you have ahead of planting for the litter to break down the less of a carbon penalty you would have versus if you make an application a few weeks ahead of planting.

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