I don't think their experiment proved excessive nitrogen fertilizer won't harm your garden, but it also failed to prove that excessive nitrogen fertilizer will harm the garden as expected.
Neat story tedln. No mention of just how mucn nitrogen was in the product they used. Bagged fertilizers vary a bunch in the amount of nitrogen. It would also be interesting to know what crop they were growing. How often do you hear that too much nitrogen will make lots of leaves but no fruit? I think that is a myth.
Yes, excessive fertilizer will kill your plants. You can test this easily with a plant in a pot. Just give it a tablespoonful a day and see how many days it takes to kill the plant.
I am not at all surprised that their test plots did much better with the addition of fertilizer. Nitrogen is the thing most often lacking in garden soils and especially if those "soils" came in a bag.
Glad your plants are looking better.
I don't remember all the details of the experiment including the crops grown on the plots. I do remember they didn't mention having a control plot which had no additional fertilizer added. They did use virgin soil which had not produced any crops except ground cover in a number of years. They tested the soil for starting NPK levels, but since their interest was in nitrogen levels, they didn't seem to pay much attention to the PK levels. I think they were trying to prove the point that suppliers of commercial fertilizing products encouraged growers to over fertilize with nitrogen in order to sell more product. They simply based the experiment on the recommended application rates the commercially available bags provided.
They assumed the suppliers were encouraging garden and home users to apply excessive amounts of fertilizers. They believed the double and triple suggested rates would kill the gardens. They probably should have used additional plots to determine the actual nitrogen concentration required to harm the plants.
They also did not perform additional soil tests to determine the current effects and long term effects on beneficial soil bacteria and salt build up in the soil from excessive nitrogen application.
They also didn't perform any run off tests to determine how much nitrogen was being washed away by normal rain into local water ways.
They had a very narrow scope experiment on nitrogen effects without considering the interrelated effects of other factors.