It has been a few years now since we have done any grid sampling but I imagine we need to be doing some. Have been pulling some composite field samples and if they come back showing a need for lime we will probably grid some before liming and VR it.

We try to make what I call "smart" grids. Since we do everything "in house" on our farm we know the fields pretty well and have old airial photos to work with as well. Many of our fields have been increased in size by combining sometimes several crop fields as well as surrounding pasture which leaves us with one larger irregular shaped field. We try to use old aerial maps to see where these old fence lines were and match our grids up so they are not straddleing these old lines. Often we find due to different cropping/pasture use over the years before the field was combined there can be significant differences in pH and fertility between these "old" fields. Also since we know our ground we may put "irregularities" in a seperate grid - like a rock outcrop area or where my dad always fed cows in the corner of one field - knowing these areas will be "diferent".

Long story to tell you our grids vary in size - typically from as little as one acre to as much as 5 but probably average about 2.5 acres. If we have ground that varies a lot we keep to 2.5 or less. We may at times even use "zones". I think we will be using a lot more zones since a lot of the ground we recently rented is terraced. Will probably use the terraces as two sides of the zone borders, chopping the area between into 2-3 acre irregular shaped "chunks". Our soil "types" don't change much within a field, topsoil depth and productivity does. For areas where soil types change a lot this would probably not work as well as using soil type for the delineation.

Lots of ways to do it but my belief is if you know your own farm pretty well you can come up with better distribution/shape of grids than what an outsider with no knowlege can do arbitrailary mechanically assigning a given size square grid.

That's my 2 cents - others mileage may vary.

John

Edit addition: "We" test for pH which for our area is probably the most important test as well as P and K and sometimes organic matter. There have been a lot of field tests done over the years that show we rarely have any micronutrient shortage that limits yield although there are rare exceptions. That is for our particular area as I know there are areas micro tests are implortant. The nitrogen test doesn't tell us much here as our topsoil is so thin what is there is subject to loss from water saturation. Further west of us in Kansas the soil nitrogen profile test gives them useful information. Independent labs will give us micro recomendations but university tests have tolds it rarely pays - "here".