What is the soil like where the Brussels sprouts are growing? As a general rule aphids tend to go to lush growth and that is usually the result of too much Nitrogne in the soil. If plants have aphids the simplest means of control is a sharp stream of water to knock the wee buggers off the plant.

The plants are grown in rows and are watered with drip tape on automatic timers. So the only thing that gets water is the plants. There hilled a bit with little weeds as I keep them under control with the old hand pulling method. Kids do this well but you have to put up with the complaints. It's hot out here.. I'm tired.. etc.

Soil condition. They had horses on the land 7 years ago and the area was not used for anything since. I've used my tractor to break up the soil and till it in. Haven't added anything to this soil. There are places where little to no weeds were living so I don't know how much nitrogen is in the soil.

Sorry to say that aphids can be found on the new growth of many kinds of plants, regardless of how they have been fertilized. It's true that we can make our plants much 'softer' and more succulent with excess N, but it is not a requirement for the aphids.

Insecticidal soaps are can be used by organic growers, as can Neem oil. Strong sprays of water can be very effective, but that means that you'll need to drag a hose around. That's a good first option if you have a hose bib nearby.

The sharp spray of water is a very effective and does not require lugging a hose around, any pump sprayer will produce that sharp water spray.
Was a good, reliable soil test done on the soil before planting? Were any of these simple soil tests done with that soil?

1. Structure. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. A good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drains too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer you soil will smell.

5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.

Is your soil clay, sand, loam, gravel?
What is the level of organic matter in that soil, the humus level?

No tests has been done on the soil. The soil apears to be more of a silt in one area greyish, sand in anonther and brown in another area. My plan is to mix them together with horse manure and mulch.

What I have found a bit wired is that when you water with a hose the water runs off the mounds more like the soil is water resistant. I used drip tape to send the water staight down and that works just fine.

Who makes a good soil testing kit? Or should this be done by a lab?

Where in the world are you? In the United States each state has an agricultural school that with the USDA cooperates in doing Ag research and has this service in each county to provide garden and farm help and advice. Canada has Ag Canada but I know little about how that works. There are also labs that do soil testing and are more expensive that if your state universities USDA Cooeprative Extension Service would.
As a general rule of thumb the soil test kits avialable to you are not reliable enough to be of any use.

I've been telling this story since 2003 so most people are tired of hearing it.

I had mentioned the sudden and permanent disappearance of aphids from my roses to one of our local organic researchers here in San Antonio. He took me into his research greenhouse to show me something. He had planted three identical shrubs each in 4-inch pots. He placed them so that their canopies touched. One of the plants was covered with aphids while the other two plants had none. NONE! What was the difference? The soil. He's a local provider of compost and was experimenting with soil additives to the basic Wal-Mart generic soil. The soil in each pot started with a Wal-Mart base but he added compost to two and added greensand to one of the compost mixes. The plant with aphids was the Wal-Mart base with no compost or greensand.

The sudden disappearance of aphids from my roses happened after 8 years of horrible infestations. All we had used on the roses for 8 years was compost. The disappearance happened the week I scattered ordinary corn meal under the roses to stop powdery mildew. That was the event that converted me to an organic program. That was in 2002. I wish I could guarantee it would work for you, but the point to me is that healthy plants have the built-in defense system that allows them to literally shed pests. Yes I have a few ladybugs, but not nearly enough to eat all those aphids. It could be the corn meal in the soil led to more of a chain reaction that allowed more aphid predators to thrive??? I don't know exactly, but it's been 5 years with no more than a handful of aphids total, for the duration.

That is really interesting about the cornmeal. I have a worm bin and we give the worms a sprinkle of cornmeal every now and then, it's supposed to be a real special treat for them.

As to the soil testing and all that. I suppose I'm more in the mode of trying thins out and recording the results to see what works best in my location/soil/etc. I may find that some things work great and others are pointless or even detramental. About all I do know is the soil is so sandy that gardening directly in it is almost more like hydroponics than soil gardening. Even the compost that comes from the county has a large percentage of sand mixed into it. I've taken to planting directly into soil amendments piled on top of cardboard and covered with mulch.