Abstract:
Tomato is widely grown vegetables in southern Ethiopia produced by small farmers for fresh fruit and for cash-generating for growers. However, the productivity of the crop is low due to many constraints of which inappropriate types and rates of fertilizer used irrespective of varietal and soil type differences are among the major constrains. Hence, field experiment was carried out in 2018/2019 cropping season to assess the effect of NPSBZn fertilizer rate on yield, yield related traits and quality of tomato varieties and to determine the cost benefit of NPSBZn fertilizer rate for tomato production. The treatment consisted of seven level of NPSBZn (0, 50, 100, 150, 200, 250 and 300 kg ha-1) and three tomato varieties (ARP tomato d2, Cochoro and Melkashola) in factorial combinations. The experiment was laid out in randomized complete block design with three replications. Results from analysis of variance showed that the crop phenology and growth traits were significantly influenced by variety and NPSBZn fertilizer except number of harvest which was not influenced by variety, but varietal difference had nonsignificant effect on number of primary and secondary branches. The main factors variety and NPSBZn fertilizer also had significant influence on number of clusters per plant, number of fruits per cluster, total and marketable fruit yield (t ha-1) and fruit pericarp thickness. Fruit set percentage; pH, titrable acidity, total soluble solid and sugar to acid ratio of fruit juice were significantly influenced by variety not fertilizer, Hawever number of marketable fruits was significantly affected by fertilizer rate not variety. The interaction of variety and NPSBZn fertilizer had significant effect on days to 50% flowering and fruit pericarp thickness. Variety, fertilizer and the interaction of the two factors had nonsignificant effects on number of flowers per cluster, number of unmarketable fruits per plant and unmarketable fruit yield (t ha-1). ARP tomato d2 variety produced the highest total and marketable fruit yield of 34.72 and 30.49 t ha-1, respectively, whereas the highest total fruit yield of 39.59 and 37.66 t ha-1 and marketable yield of 35.27 and 33.86 t ha-1 were produced by the application of 300 and 250 kg ha-1NPSBZn fertilizer, respectively. ARP tomato d2 and Cochoro varieties with the application of 250 kg ha-1 NPSBZn fertilizer had 7.11 and 6.677 mm thick fruit pericarp, respectively. ARP tomato d2 and Cochoro varieties had higher titrable acidity and pH of fruit juice, respectively, whereas ARP tomato d2 and Cochoro varieties had higher total soluble solid and sugar to acid ratio. The higher marginal rate of return (MRR) of 4272% with net benefit of 349116 Birr ha-1 obtained from ARP tomato d2 variety when supplied with 200 kg ha-1NPSBZn fertilizer, however, this variety also gave an option when supplied with 250 kg ha-1 NPSBZn fertilizer which offered highest net benefit of 380126 Birr ha-1 and had third highest MRR of 4118%. This variety when supplied 150 and 100 kg ha-1 NPSBZn fertilizer also had second and fourth higher MRR of 4251 and 4031%, respectively and Growers with varied interest and preference could select one of these options, however, considering the highest volume of fruit yield produced, net benefit and acceptable MRR, it is suggested to grow ARP tomato d2 variety with the application of second 250 kg ha-1 NPSBZn fertilizer and Cochoro variety with 300kg ha-1 NPSBZn in the study area. However, it is recommended to conduct the experiment at different locations to make sound recommendation.