Might be a nutrient imbalance or a too wet soil. Excess Potash levels can inhibit a plants ability to properly utilize Nitrogen. Might be a soil pH problem which can also prevent plants from utilizing nutrients.
The nutrients in organic materials are not very readily available until the Soil Food Web makes them available to plants, although many of the nutrients in animal manures are fairly water soluble. Organic matter does hold moisture in the soil, but too much organic matter can hold too much soil moisture.

Yeah, I thought about the water. It's good draining soil on a slope in a warm dry climate...seems hard to over water here, especially squash and melons. But it still could be that....of course with that much organic material it could hold water/displace air where the roots are trying to eat.

PH is good. The problem I see with spending for soils test is that the garden is an acre with areas of very different history of use since starting it from all native soil a few years ago( good P&K no N originally). Some has seen compost 5 or more times and some only 1 or two times and some is still native soil not yet ammended or planted.

I have the basic soils test kit I don't find Potash to be through the roof, it is right around "sufficient". I need to get some more N capsules and find out if nitrogen is still there... certainly seems it should be.

O.K.,
A few closing comments on this exciting thread.
First thanks, Kimmsr for your comments. I read a few scholarly articles on the possibilities you presented which where very informative. It could be imbalance. I dug some soil up, it was wet, looked great otherwise, no smells or mold or anything. The roots from a plant I ripped out looked fine but there was none of the good white stuff I usually see when I dig up an active bed.

It could be too much water, no green veins are present like in iron deficiency. But I will take one professional soil sample anyway. That could be a good starting point for eliminating guess work in solving future mysteries such as this. I do have pretty good soil I know that.

Another update in case anyone ever searches this topic. Nitrogen did in fact leach from the compost that I had added to the planting area. I tested the planting area with the yellow plants and the compost pile that I drew from for planting. The planting area shows low nitrogen and the compost pile is very high(p & k good in both). I was over watering and that's part of it both on the leaching side and just somewhat drowning the plant.

The Nitrogen in compost is not very readily available and therefore does not appear on most tests. That does not mean the N is not there simply that it is not very readily available and needs to be worled on by the Soil Food Web to become available to plants. The N in compost is more stable then the N in animal manures.
The test you did does not necessarily reflect that your compost is deficient in Nitrogen.

It is hard to make any judgement without knowing what climate you are dealing with, and underlying soil type. That only the squash are having this problem is curious and undoubtedly significant.

O.K. I realize that I put 6 gallons total of compost into the hills of squash and it's basically a fail. Last year I put about 20 gallons per hill and still got much yellowing but not failure.

Anyway about nitrogen being locked up in the soil, I guess that happens but it's readily available in the compost I added as per test, so my conclusion for now is what my neighbor said, that It leached out of the root zone.

As suggested by pnbrown climate and soil type could have lots to do with this in combination with the way the drip is set up on each hill. First off I planted in large holes on sloped land in native soil, sandy loam to just plain sandy, which is devoid of nitrogen. The situation is a little more like container gardening in the desert.

I have a 5 foot coil of micro tubing with half gallon emitters around the squash plants in the hills and that is the only watering it gets due to the fact that we have practically no rain from Apr. to Nov. or later.

In my other bed the drip is laid out in flat rows and I am thinking it is likely that soluble nitrogen migrates around in the beds more normally as opposed to being drug out of the root zone.

Conclusion, some other form of feeding will be helpful for best results with this planting method I am using.

Anyway, thanks for helping with ideas/thoughts.

Given that I am using drip, it would be nice to have all the fertility needs of the plants done at planting time. P&K are sufficient always, so it's just N.

Any suggestions for what would do the nitrogen job for 100 days in this situation? Maybe good suggestions for how to safely side dress when vines start running?(as is often suggested on seed packs). Can I dig something in around the drip without hurting the shallow roots at about 40 days after planting?

Thanks.