The fruit yield/ha of bitter gourd was significantly influenced by different treatment combinations (Table 1). Fertilizer application in general increased fruit yield from 6.47 to 19.90 t/ha in 2010 and 8.50 to 20.15 t/ha in 2011. The highest yield (19.90 t/ha in 2010 and 20.15 t/ha in 2011) was obtained from N120 P40 K80 S30 treatment and it was significantly different from all other treatments. Sanap et al. (2010) reported that application of 250 kg N, 50 kg P2O5 and 100 kg K2O/ha significantly increased the yield of bitter gourd in India. Islam and Irabangon (1994) also observed that application of 240-120-60-kg NPK/ha markedly improved the number of fruiting and yield of bitter gourd. Rajan and Markose (2005) reported that the maximum fruit set and yield were obtained with 90: 25:50 kg NPK/ha. The maximum yield/ha produced by N120 P40 K80 S30 treatment was mainly due to cumulative effects of number of fruits/plant, fruit size, and fruit weight. The experimental soil was highly deficient in different nutrients. So, the application of different nutrients to the soil resulted in the highest uptake by plants which ultimately helped increase production of assimilates that causes higher fruit size and yield. Plants grown without added fertilizer (native nutrient) produced the lowest yield (6.47 t/ha in 2010 and 8.50 t/ha in 2011). The
The yield increase over control due to single effect of NPK and S are shown in Table 2. Nitrogen application up to 120 kg/ha increased yield significantly and thereafter decreased. Application of 120 kg N/ha increased yield of bitter gourd by 86% in 2010 and 54% in 2011 over the control. Yield of bitter gourd also increased significantly due to application of P up to 40 kg/ha and further increase in P decreased the yield. Fertilization with K also followed the same response on yield (Table 2). The yield varied from 14.07 to 18.56 t/ha in 2010 and 13.65 to 17.85 t/ha in 2011 due to different levels of K application. Yield of bitter gourd also increased with the increase rate of S up to 30 kg/ha and then decreased. The result indicates that the yield increased with the increase of N, P, K, and S application up to certain limit. Effect of N and P was distinct in comparison to K and S. Table