The soil in the garden is poor. Much clay, poor drainage. What should I add to the soil to give it a higher nitrogen level? When should I add it? Is there a kit to ascertain the levels of needed minerals?
Nitrogen alone will not correct the soil deficiencies you have described. Bob Bricault of MSU has written a brief and informative article about creating healthy garden soil, which you can find here: http://migarden.msu.edu/uploads/files/Healthy_soils.pdf. This article will provide you with a good understanding of what amendments your soil MAY need to create healthy soil in your garden, but to get a definitive answer specific to YOUR soil, you should have a complete soil test done, with recommendations specific to the nutrients and other matter needed by your soil to make it productive for you. One place to obtain such a soil analysis is here: http://www.msusoiltest.com/