After a long trip – this one to start the year was a particularly long one for me – I usually have some passages or topics to look up in my library when I get home.
This time was no exception. I was checking Carrow et al. (Turfgrass Soil Fertility and Chemical Problems) on page 166 to refresh my memory with their advice on fertilizer recommendations.
“One approach is to meet the immediate needs of the plant, and the other is to build soil levels to an optimum level as well as meet plant requirements. These approaches are commonly referred to as ‘sufficiency’ and ‘buildup and maintenance,’ respectively. Higher recommendations are used if the aim is to build soil levels.
They continue, and this is the paragraph I wanted to read:
“A less appropriate approach to fertilization that is sometimes, although infrequently, suggested is to replenish nutrients removed by the plant. This approach is not based on soil testing but on the weight and nutrient concentration of the clippings. Such an approach assumes that clippings are removed and neglects nutrient fixation, leaching, and other processes that reduce the availability of applied nutrients. If replenishing nutrients removed was a reasonable option for fertilization, then return of clippings should provide the necessary nutrients.”
I wondered what Madison had to say on this topic – his Principles of Turfgrass Culture (1971) has two chapters about nutrition. I made a new slide with this quote:
He wrote that “with clippings returned, and if soil tests indicate adequate levels, there may be no need for added phosphorus.” And “when clippings are returned, little potassium fertilizer should be needed on most soils.”
I like the approach we take with MLSN. We base it on soil testing, and also replenish nutrients used by the plant.
I’ve often explained that this is not the way to think of turf nutrition:
That’s because N controls the growth and consequently the demand for all other nutrients:
As I continued reading, I came across this on page 206 of Madison:
“A different aspect of nutrient availability is considered by Liebig’s Law of the Minimum. Liebig was a 19th century chemist who initiated the use of chemical fertilizers. As Liebig saw things, and stated in his law, if one necessary element is deficient and all others are adequate, growth will be limited by the one that is missing. That is a reasonable statement.
In recent years Liebig’s Law has been presented to turf audiences in a different and incorrect form. Instead of one shartage with all other supplies adequate, the law is presented as if a number of minerals were short in varying degrees and the Law is stated as “the necessary factor in shortest supply limits growth.” The discussions accompanying this version of the law emphasize the error. The speaker suggests that if, for example, phosphorous [sic] is in very short supply and nitrogen in moderately short supply that you can get no further growth from added nitrogen until phosphorus is first added. This is not so. In that example, added nitrogen would increase growth. The plant tissues would contain a smaller percentage of phosphorus, but because there was more tissue the total phosphorus taken up would be greater than without the added nitrogen.”