Release characteristics of organic fertilizers

Leaching and nutrient uptake by grass was used to study the nutrient release characteristics of seven commercial and experimental fertilisers. An inorganic soluble and a controlled release fertiliser (CRF) were included for comparative purposes. The effect of addition of organic fertilisers to peat on bacterial and fungal activity was also studied. The results showed that over a period 140 days with seven leachings, the organic fertilisers released between 25% and 60% of their N content. Most of the N release occurred within the first 56 days. By contrast the N release pattern of the CRF was very even while the soluble fertiliser released nearly all its N content at the first leaching. The pattern of release for P and K for the CRF and the soluble fertiliser was similar to that of N. The P and K release characteristics of the organic fertilisers were much faster than for N. The addition of organic fertilisers to peat fertilisers to peat resulted in increased bacterial and fungal activity. Tomato seedling growth with some of the organic fertilisers was equal to that with soluble fertiliser but the efficiency of N in organic fertilisers was lower.