Soil Fertility Soil Fertility • Inorganic fertilizers Inorganic fertilizers – Most developed in the 1940’s Most developed in the 1940’s – Ammonium nitrate Ammonium nitrate – Superphosphate Superphosphate – Muriate of potash Muriate of potash – These are often pure (do not contain These are often pure (do not contain micronutrients) micronutrients) – These are often concentrated (therefore These are often concentrated (therefore they are cheaper to transport and apply) they are cheaper to transport and apply)
– Most developed in the 1940’sMost developed in the 1940’s– Ammonium nitrateAmmonium nitrate– SuperphosphateSuperphosphate– Muriate of potashMuriate of potash– These are often pure (do not contain These are often pure (do not contain
micronutrients)micronutrients)– These are often concentrated (therefore they are These are often concentrated (therefore they are
cheaper to transport and apply)cheaper to transport and apply)
Soil FertilitySoil Fertility• NitrogenNitrogen is often the most limiting is often the most limiting
nutrient in soilsnutrient in soils
• NitrogenNitrogen applied in excess causes applied in excess causes reduced flowering and fruiting and reduced flowering and fruiting and greater vegetative (leafy) growthgreater vegetative (leafy) growth
– Percentage (by weight) of the available Percentage (by weight) of the available Nitrogen (as N), Phosphorus (as PNitrogen (as N), Phosphorus (as P22OO55) and ) and
Potassium (as KPotassium (as K22O)O)
Ex: 5:10:5 Ex: 5:10:5
5% N 5% N
10% P 10% P
5% K5% K
80% in the bag is inert material!80% in the bag is inert material!
– Ex: 30 lbs. of N,P,K in a 100 lb. bag of fertilizerEx: 30 lbs. of N,P,K in a 100 lb. bag of fertilizer– Less costly (don’t pay for a lot of “filler”, but tricky to Less costly (don’t pay for a lot of “filler”, but tricky to
apply)apply)
• Low analysisLow analysis = N+P+K percentage = N+P+K percentage << 30% 30%– more costly due to weight in transport but easier to more costly due to weight in transport but easier to
applyapply
Soil FertilitySoil Fertility• Fertilizer ratioFertilizer ratio
– The proportion of the three major elementsThe proportion of the three major elements
Ex: 5:10:5 = 1:2:1 ratioEx: 5:10:5 = 1:2:1 ratio
Soil FertilitySoil Fertility• N-recommendations: (in lbs./acre)N-recommendations: (in lbs./acre)
• If the soil test indicates that you need to apply If the soil test indicates that you need to apply 100 lbs. of N per acre, how many pounds of a 100 lbs. of N per acre, how many pounds of a 20:10:10 fertilizer would you need?20:10:10 fertilizer would you need?
20% • X = 100 lbs.20% • X = 100 lbs.
0.20 • X = 100 lbs.0.20 • X = 100 lbs.
X = 100 lbs./0.20X = 100 lbs./0.20
X= 500 lbs.X= 500 lbs.
Soil FertilitySoil Fertility• Now… you probably don’t have a garden Now… you probably don’t have a garden
that is an acre in size.that is an acre in size.
• Ex: If your garden is 20’ x 20’ = 400 ftEx: If your garden is 20’ x 20’ = 400 ft22
20’20’
20’20’Your Your
gardengarden plotplot
1 acre =1 acre =43,560 ft43,560 ft22208.5’208.5’
208.5’208.5’
Soil FertilitySoil Fertility
500 lbs500 lbs X lbs.X lbs.
43,560ft43,560ft22 400 ft400 ft22
43,560 • X = 200,00043,560 • X = 200,000
200,000200,000
43,56043,560
X = 4.59 lbs. of fertilizer per 400 sq. feetX = 4.59 lbs. of fertilizer per 400 sq. feet
