31 Fertilizer numbers

first_imgVolume XXIXNumber 1Page 31 By Clint WaltzUniversity of GeorgiaAll plants require nutrients to grow and develop properly.Various nutrients affect plants differently and are needed invarying amounts.Essential nutrients are just that: essential. Plants have to havethem to sustain the vigor they need to resist environmentalstresses, weeds, diseases, insects and other pests.The 16 essential nutrients are broken into two categories,primary (nitrogen, phosphorus and potassium) and secondary(calcium, magnesium, sulfur, iron and others).The primary nutrients get the most attention because they’rerequired in the greatest amounts. Fertilizers are sold based ontheir amounts.The numbersOn a fertilizer bag, the numbers refer to the percentage ofactual nitrogen (N), phosphate (P2O5) and potash (K2O). So 10percent of the weight of a bag of 10-10-10 is nitrogen, 10percent is phosphate and 10 percent is potash.It’s easy to figure the actual weight of nitrogen. The percentageis listed on the bag. In a 50-pound bag of 10-10-10, the nitrogenwould weigh 5 pounds (0.10 times 50).It’s not as simple, though, for phosphorus (P) and potassium (K).To find the amount of phosphorus, multiply the phosphate numberby 0.44. Get the potassium amount by multiplying the potashweight by 0.83.How it adds upSo that 50-pound bag of 10-10-10 has 5 pounds of phosphate times0.44, or 2.2 pounds of phosphorus. It has 5 pounds of potashtimes 0.83, or 4.15 pounds of potassium. With the 5 pounds ofnitrogen, then, it has 11.35 pounds of primary nutrients.Using the same formula, a 50-pound bag of 16-4-8 would have 8pounds of nitrogen, 0.88 pounds of phosphorus and 3.32 pounds ofpotassium. That’s 12.2 pounds of primary nutrients.So what’s the rest of the weight in the bag? Some of it may besecondary nutrients. The rest is filler material to make iteasier to apply.A fertilizer bag containing all three nutrients is considered a”complete” fertilizer. A product with any nutrient missing iscalled “incomplete.”(Clint Waltz is an Extension Service turf scientist with theUniversity of Georgia College of Agricultural and EnvironmentalSciences.)last_img read more