from fertilizer. If the soil contains more of an element than the grass requires, that element is not required as fertilizer. If the soil doesn’t have enough, that element should be applied as fertilizer.
element required as fertilizer as Q. a + b − c = Q where, a is the quantity of the element used by the grass b is the quantity of the element required in the soil c is the quantity of the element present in the soil Q is the quantity of the element required as fertilizer
of locked-up nutrients ▶ Focusing on what an element does, rather than how much is present ▶ Looking at percentages of elements rather than quantities ▶ Water or saturated paste extracts to look at availability ▶ The idea that an element can be exchangeable but not available
K is 50 ppm and the annual N rate is 16 g m-2. a + b − c = Q In g m-2, a = 8, b = 5.5, c = 7.5. In ppm, a = 54, b = 37, c = 50. amount needed 54 + 37 − amount present 50 = fertilizer requirement 41 Convert between 3-dimensional (ppm) and 2-dimensional (g m-2) based on rootzone depth and soil bulk density. For a 10 cm deep rootzone with bulk density of 1.5 g cm-3, 1 g m-2 equals 6.7 ppm. Using that conversion, Q of 41 ppm is a K requirement of 6.1 g m-2.