A research entitled the effect of various sources of organic matter on improvement of N,P,K Nutrient of Ultisol was conducted in Limau Manis Padang. The research was aimed to investigate the contribution of different source of organic matter to improve N,P,K content in soil. Field research was arranged in Randomized Block Design (RBD)  consisting 5 treatments and 3 replications (blocks). Treatments are : A = no organic matter added, B = Tithonia, C = Paddy Straw, D = Imperata cylindrica, and E = Leucaena glauca. The dosage for each treatment was 20 ton/ha. The result showed that tithonia gave the best contribution in improving N,P,K content of Ultisol Limau Manis.Keywords :organic matter, N, P, K of Ultisols.

7 PENGARUH PEMBERIAN BEBERAPA J ENIS BAHAN ORGANIK TERHADAP STABILITAS AGREGAT TANAH ULTISOL LIMAU MANIS Yulnafatmawita, Adr inal, dan Anita Febr iani Daulay Laboratorium Fisika Tanah Fakultas Pertanian Universitas Andalas Abstr actA field research about the effect of some sources of organic matter on aggregate stability of Ultisol was conducted in Limau Manis Padang. The research was aimed to investigate the contribution of different sources of organic matter to soil aggregate stability. Field research was arranged in Completely Randomized Block Design (RBD) consisting of 4 treatments (types of organic matter) and 3 replications (blocks). The treatments were : A = Tithonia diversifolia, B = Straw of Oryza sativa, C = Imperata cylindrica, and D = Leucaena glauca. The dosage for each treatment was 20 ton/ha based on dry weight. The result showed that Tithonia diversifolia gave the best contribution in improving soil aggregate stability of Ultisol Limau Manis for the first three (3) months.