Potassium Release From Coffee Husks As Affected by N Fertilization.

There is evidence that the mineralization of coffee husk used as organic fertilizer is slower than desired. The present study aimed to assay K contents on soil amended with coffee hulls as affected by N application. A soil column experiment was conducted using coffee husks from the processing of dry coffee beans. The K contents were evaluated at four depths: 0.00-0.05, 0.05-0.10, 0.10-0.20 and 0.20-0.40 m after the application of the equivalent of 0, 80, 160, 240 and 320 kg ha^-1 of N as ammonium nitrate, in the presence and absence of 10 ton ha^-1 of coffee husks. An average precipitation of 1285 mm was simulated by applying water to the columns two times a week over five months. At 50, 100, and 150 days after application, four columns representing each treatment were sliced into sections and analyzed for K contents at all depths. The nitrogen application improves K release from coffee husks and also K leaching . At day 50, for all treatments that received N, concentrations of K was increased at all depths compared to the original untreated soil. Soil K concentration at depths 0.05-0.10, 0.10-0.20, and 0.20-0.40 m increased in accordance to increase in N levels applied. 100 days after applications, the patterns of K release from coffee husks had followed the same behavior observed at day 50. Although all N levels plus coffee husks resulted in an increase in K concentrations across the depths, the biggest K leaching occurred with the treatment receiving the most N plus coffee husks. At day 150, N treatment levels 160, 240 and 320 kg. ha^-1 plus 10 ton ha^-1 coffee husks resulted in significant increases in K concentrations at all depths, while treatments receiving coffee husks only, and coffee husks plus 80 kg N ha^-1 possessed similar K concentrations. Regardless of the evaluation period (i.e. day 50, 100, or 150), higher N applications resulted in greater K release from coffee hulls.