Effect of Intercropping Onion with Sugar Beet on Productivity of Both Crops and Root-Knot Nematodes Control under Different Onion Plant Densities and Slow-Release N Fertilizer Rates

A field experiment was conducted over two growing seasons 2018/19 and 2019/20, at Ismailia Agric. Exper. and Res. Station, A.R.C., to determine the effect of onion plant densities (2, 3 and 4 rows of onion intercropped with sugar beet) and four nitrogen fertilizer rates (60, 80 and 100 kg N/fad) as blending fertilizer of urea formaldehyde (UF as slow-release N) and traditional urea (TU) compared to control treatment (100 kg N/fad as TU) on productivity, control of root-knot nematodes Meloidogyne spp., land and N use efficiency as well as net return. Results showed that, intercropping two rows of onion with sugar beet significantly increased root, top and sugar yields/fad of sugar beet, TSS% and bulb characters as well as NUE compared to 3 and 4 rows of onion. Meanwhile, increasing onion plant density up to four rows significantly increased plant height and onion yield/fad. Slow-release N fertilizer had a significant effect on sugar beet and onion traits. The blending fertilizer of UF at 100 kg N/fad had the highest sugar beet and onion productivity, while N rate at 80 kg/fad had the highest sugar yield/fad and NUE. Intercropping two rows of onion with application UF+TU at 100 or 80 kg N/fad had the highest values of sugar beet and onion traits, without significant differences in most cases. The applying treatments were studied against root-knot nematodes under field conditions. Generally, the nematode parameters were negatively correlated with intercropping onion with sugar beet compared to check treatment (solid sugar beet). The most effective treatment in reducing the number of galls, egg-masses per root system, root gall index (RGI), egg -masses index  (EI) as well as a number of second-stage juveniles (j₂) in soil was  4 rows with 80 kg nitrogen in two successive seasons. Intercropping two rows of onion with sugar beet and application blending N fertilizer of UF at 80 kg N/fad had the highest LER value 1.31 and 1.34 and maximizing net return/fad compared to solid sugar beet. Therefore, growing two rows of onion with sugar beet that received 80 kg N/fad as a mixture of UF and TU could be controlled root-knot nematodes, Meloidogyne spp. and increased sugar beet productivity, maximizing land use and grower profitability as well as reduced N fertilizer usage.