EFFECTS OF ORGANIC AND INORGANIC NP FERTILIZERS ON THE PERFORMANCE OF GARLIC (Allium sativum L.) VARIETIES AT KOGA, NORTHWESTERN ETHIOPIA

Garlic (Allium sativum L.) is an important cash and spice crop produced for home consumption and as a source of income to many smallholder farmers in many parts of the Ethiopia. However, the yield of the crop is often constrained by low and imbalanced nutrient supply in the soil. Therefore, a field experiment was conducted at Adet Agricultural Research Center, Koga irrigation trial site in 2015/2016 cropping season with the objectives of assessing the effects of combined application of vermicompost and NP fertilizers on the performance of garlic varieties and determining the economically profitable fertilizer rates for higher yield of garlic under irrigation. Three garlic varieties (Bishoftu Netch, Tsedey and a local cultivar) and six forms of fertilizer [no fertilizer;128/92 kg ha-1 N and P2O5 (recommended nitrogen and phosphorus, RNP); 5 ton ha-1 vermicompost (VC); 50% RNP + 5 ton ha-1 VC; 50% RNP + 2.5 ton ha-1 VC and 100% RNP + 2.5 ton VC ha-1) were tested in 3 x 6 factorial arrangement in Randomized Complete Block Design with three replications. The results showed that both varieties and forms of fertilizer had significant interaction effect on all characters except the non significant interaction effect on days to emergence, number of leaves per plant, mean clove number, unmarketable bulb yield and bulb dry matter percent. Bishoftu Netch variety gave significantly the highest total and marketable bulb yield 8.65 and 8.50 ton ha-1, respectively, that exhibited 24 and 57% advantages over Tseday and the local cultivar, respectively. The highest values of mean bulb weight (34.90 g), mean clove number (10.89), mean clove weight (5.31 g), total fresh biomass yield (44.82 g/plant) and bulb dry matter (20.64%) was obtained from treatments that received 50% RNP + 5 ton ha-1 VC. Bishoftu variety gave the highest benefit of Birr 296053.35 and 285566.67 per ha at 100% RNP alone and 50% RNP + 5 ton ha-1 VC, respectively that was 31% and 58% higher than Tseday and local cultivar at 100% RNP only and 27% and 63% higher than Tsedey and the local cultivar at application of 50% RNP + 5 ton ha-1 VC, respectively. According to the partial budget analysis, the highest economic benefit was recorded from Bishoftu variety at the application of RNP only. Therefore, it can be concluded that producers in the study area could use Bishoftu Netch variety using the recommended inorganic NP fertilizer alone for optimum garlic production and maximum economic benefit. However, for sustainable soil health conditions on successive crops, combinations of 50% RNP and 5 ton ha-1 vermicompost for all varieties could be used