Abstract

This study evaluated the effect of bioslurry from on-farm biogas production units and other sources of nitrogen fertilizer on Irish potato yield and yield components in northern Rwanda. To achieve this, an on-farm experiment was undertaken in the Andisols of Musanze District and the Oxisols of Gicumbi District in 2012. Three farms were selected to host the study in each District. Six treatments were randomly tested in unreplicated field strips by farm, one treatment by strip. The treatments comprised of i1) a control with no fertilizer (CTL000); i2) a control supplying 100% of recommended N rate from chemical fertilizers (MIN100); i3) a treatment supplying 100% of recommended N rate from farm yard manure (FYM100); i4) a treatment supplying 40% of recommended N amount from bioslurry and 60% from mineral N fertilizer (BIO040); i5) a treatment supplying 60% of recommended N amount from bioslurry and 40% from mineral N fertilizer (BIO060); and i6) a treatement supplying 100% of recommended N amount from bioslurry (BIO100). The results indicated that locally produced bioslurry appeared very low-nitrogen concentrated and for some farms, more than 100 m3 /ha of bioslurry was needed to meet potato nitrogen requirements. Bioslurry appeared as effective as or better than conventional nitrogen sources to improve soil properties such as soil pH and organic matter content, and to sustain potato growth and tuber yield and quality. This was particularly true when bioslurry was combined with mineral fertilizer. In that regard, bioslurry can contribute between 40 and 60% reduction of mineral fertilizers with no subsequent reduction of market or total potato tuber yields.

Key words: Bioslurry, organic fertilizer, mineral fertilizer, organic sources, soil quality, potato yield.