When anyone makes the claim, "This fertilizer won't burn," my immediate reply is, "Then it won't feed, either." The identical property which makes food elements available as plant nutrients-high solubility-will also make them likely to "burn" or injure plant tissues. The burn may be immediate or it may be delayed, but if the soluble ingredient which causes this condition is present in excess amounts, burn is almost inevitable.
A SOD STORY
On lawns, for example, a burn from an overdose of a chemical fertilizer such as ammonium sulfate becomes visible almost at once, while a too-heavy application of sewerage sludge may not show any ill effects for a month or two after application to the turf. Unfortunately, the burn from organic sources comes so much later after application that it is seldom traced to its cause. Nevertheless, because it happens in summer-a time when grass is peculiarly susceptible to severe injury-a delayed organic nitrogen burn of this kind usually causes more permanent injury than does a burn inflicted early in the season by a chemical fertilizer.
To understand how all this happens let us look at two lawn areas, one fertilized heavily with a highly soluble chemical like ammonium
nitrate and the other with sewerage sludge (a typical organic fertilizer). In the first instance, the owner applies 10 pounds of ammonium nitrate in spring soon after grass begins to grow. He fails to water it in, and so the chemical fertilizer begins to suck moisture out of the grass plants to satisfy its "thirst." In a matter of a few days, the entire lawn is dappled brown and green-severe nitrogen burn. After the owner realizes his mistake, he waters heavily to wash out the excess salts; the grass gradually recovers and turns dark green. By June it is healthy and ready for another feeding. This time the owner waters it in and no burn results.
The same week in early spring the second lawn, perhaps next door to the first and on the same type of soil, is fed with sewerage sludge because the owner is convinced this organic fertilizer will not burn. He applies SO pounds per 1,000 square feet of lawn. April and May remain cool, however, and because soil bacteria are inactive the organic material is not broken down and this first application produces no results. The owner, certain he needs more fertilizer, dumps on another 25 pounds of sludge per 1,000 square feet. The two applications contribute less than four pounds of actual nitrogen per 1,000 square feet, not an excessive amount by any means. If organic nitrogen were really non-burning, he would have no trouble.