When buying soil for growing coffee, the following values are recommended for coffee soil (Malavolta, 201):
P (resin) – 15-30 µg/cm3.
P (Mehlich 1): 10-20 ppm
SO4-S: 10-15 µg/cm3.
K% CEC (pH 7.0): 10-15%
Ca% CEC (pH 7.0): 40-60%
Mg% CEC (pH 7.0): 10-15%
V%: 60-70%
CEC (pH 7.0): 7-10 meq/100 cm3.
B (hot water): 0.4-0.5 ppm.
B (0.05 N HCl): 1.0-1.2 ppm.
Cu (Mehlich 1): 2-3 ppm.
Zn (Mehlich 1): 4-7.
Analysis of Soil: Correcting Problems
Lime is often used to help correct acidic soils to a pH between 4.5-5.5 in the first 20 cm of soil. When planting coffee, the holes sCoffee Fertilizerould be covered with 250-500 g of limestone per meter (Mavolta, 199). Production increases of up to 500% have been observed by adding limestone. In Brazil the highest producing plantations had a pH from 6.0-6.5, a cation exchange capacity of 40-50%, and the base saturation in the upper 20 cm was 60% (Malavolta, 198). The requirement for lime can be calculated as follows:
Lime needed = (T(V1-V2)/RPTN)p where
T – meq/100 cm3 of exchangeable H+Al+K+Ca+Mg
V1=S/T*100
RPTN=Relative Power of Total Nutrition. The average is 75%.
p=factor of compensation for depth:
= 0.5 for 0-10 cm.
= 1.0 for 0-20 cm.
=1.5 for 0-30 cm.
(From Malavolta, 198).
To correct problems with acidity below 20 cm deep phosphogypsum is often applied. Mavolta suggest that phosphogypsum should be applied when aluminum saturation is higher than 20% or the participation of Ca in the effective CEC is lower than 40% (Malavolta, 200).
Coffee Fertilizer
Since the coffee hullls and pulp are rich in nutrients, many people often use coffee grounds as fertilizer. One 60 kg bag of coffee contains 1,026 g of nitrogen, 60 g of phosphorous, 918 g of potassium, 162 g of calcium, 90 g of magnesium, 72 g of sulfur, 0.96 g of boron, 0.80 g of copper, 3.6 g of iron, 1.2 g of manganese, 0.002 g of molybdenum, and 0.72 g of zinc (Malavolta, 197). The pulp resulting from processing contains 1,068 g of nitrogen, 84 g of phosphorous, 2,250 g of potassium, 246 g of calcium, 78 g of magnesium, 90 g of sulfur, 2.04 g of boron, 1.08 g of copper, 9.0 g of iron, 1.80 g of Manganese, 0.004 g of Molybdenum, and 4.20 g of Zinc (Malavolta 197).
Mineral deficiencies in mineral content can usually be detected visually from looking at the coffee bean leaves. See Coffee Bean Leaf Analysis for more information on laboratory tests available.