Use some urea, its 46% nitrogen.

my home soil test kit indicates virtually no nitrogen

Your "home soil test kit" is wrong IMO. You have increased the nitrogen too far and burned the root system.
Get a real soil test.

Many forms of Nitrogen are very water soluble and if not used by plants fairly quickly the available N is washed out of the soil with water as it drains. Soil temperature also can influence available N, although in Ca that should not be a reason. More than likely there is too much undigested organic matter that the soil bacteria are working on and utilizing the N to the detriment of the plants.

Or your problem may have nothing to do with nitrogen. Lots of stuff will turn a plant yellow. As stated above, get thy soil to a lab.

Run microsprinklers for 6 minutes? Wow, I'm surprised the plants are upright. With that, very little of your growing media is being moistened.

Far too little water, and likely contributing to their problems. Likely you need to run the system far longer.

To determine how long to run the system, try 30 minutes, then stop. An hour later stick a trowel in it to determine how deep the moisture went.

If you think that's far too long as a starting point, run the system for the usual 6 minutes, stop, then an hour later check.

It is not possible to get an accurate N reading from a home soil test kit. Even many professional soil testing labs do not test for this nutrient.

N is the most mobile of the three primary plant nutrients and is very difficult to assess. It will read differently based on time of year/time of day, whether the area is in sun or shade, how much moisture is in the soil, quantity and type of organic matter and a host of other various factors. At best, you will only get an approximate reading at that point in time. It is also the single nutrient that is most often naturally lacking or deficient in an unamended cultivated garden.

Blood meal is a good source of fast acting organic N but sometimes it is too fast :-) In a warm, humid environment, blood meal will convert to ammonia rapidly and this can often burn fragile roots. You need to be very careful with your application rate - no more than a pound per 100sf. A slower, less soluble source would be better. Together with the organic matter of the compost, I'd guess the blood meal plus fish emulsion may have created too high a N level, at least temporarily. And I don't think this is aided by your watering practices (which would flush the excess soluble N) - 6 minutes is not a sufficient duration for any kind of proper soil depth penetration or to satisfy the needs of young, rapidly growing seedlings. It is far better to offer water at the root zone (not with sprinklers, where most evaporates before it hits the ground) for a longer duration and less frequently. You want to check and make sure the water penetrates down into the soil at least 6-8 inches. The bark, if applied very heavily, may also be impeding water penetration as well. I dislike bark for a veggie garden. Better to use a finer textured mulch - chopped grass trimmings, shredded leaves, compost, composted manures, etc., as these will help to retain soil moisture rather than repel it.

I have the same problem. Native soil is nitrogen depleted, but I live at the tundra. I worked organic matter into the soil (but not manure) but still levels are defficient.

Indoors, levels of same soil worked, have strong nitrogen levels and plants grow well.

The reason is because it rains a lot, every day, so it washes out all the nitrogen, even if the soil is clay.

I can't find solutions, but at least always have a cover ground crop, and use a lot of nitrogen fixing species everywhere.

Also adding too much organic matter temporarely locks the nitrogen from the soil.

Quick additions of nitrogen (even as liquid compost or urine) do not work long-term, because plants can only use as much nitrogen as possible, before the rest is leached out in my rainy climate.

Nitrogen availability is very dependent on soil temperature and the activity of the Soil Food Web, as well as a number of other factors relating to the soil. To a point organic matter in the soil can help hold N in place but too much OM can be as bad as too little and cause the SFW to be preoccupied with digesting that extra OM and utilizing the N for that purpose.
While many people think yellowing of plants indicates N deficiency that is only one of the causes of Chlorosis and throwing a source of N at the soil may not be the solution. A good in depth look at that soil, including a good reliable soil test from a good soil testing lab, is needed to determine what the real problem is.

Given what you've done your problem probably isn't a lack of N. Second, those home soil test kits are very unreliable - if you want to know what's In your soil you need an analysis from a reliable lab. Third, having no detectable nitrate N is not at all unusual, even in very fertile soils with adequate N-sources to provide for plant nutrition. I just got a test back from my state lab, and as usual it shows zero nitrate N, which is usual in my hot, humid Gulf coast environment. Still, everything grows pretty well.

Some other common causes for slow growth and chlorotic (yellow) appearance are low sulfur, low iron or zinc, and high phosphorous which leads to poor availability of iron and zinc. There are others, but those are common. Low S is frequently mistaken for low N.

The link below may help you understand the myriad nutrient causes of chlorosis. Since you really don't know what's in that soil, I'd suggest starting with a good soil test. If you're in CA I believe you don't have a state lab, but I've heard good things about A&L Western Labs:
http://www.al-labs-west.com/

Here is a link that might be useful: Plant Nutrients - Deficiency & Toxicity Symptoms