GROWTH AND NUTRITIONAL STATUS OF SWEET PEPPER (CAPSICUM ANNUM L.) ARE CO-INFLUENCED BY NITROGEN APPLICATION AND MELOIDOGYNE SPP. INFECTION

Abstract

Sole ammonium is known to negatively affect plant growth and also reduce rhizophere pH. Interestingly low pH negatively affects nematode growth. On the other hand, nitrates enhance plant growth but increase plant exudates that attract nematodes. A greenhouse experiment was set up at Kenyatta University to evaluate the effect of nitrate (NO₃^--N) and ammonium (NH₄⁺-N) concentrations with and without nitrification inhibitor applied at 50,100 and 200 parts per million (ppm) nitrogen (N) on sweet pepper (Capsicum annum L.) infected with root-knot nematode Meloidogyne spp on growth and nutrient composition. The plant height, leave area, plant weight, and the concentration of N, phosphorous (P), potassium (K), calcium (Ca), magnesium (Mg), manganese (Mn), iron (Fe), copper (Cu) and zinc (Zn) in the leaves were determined at 60 days after nematode inoculation. NH₄⁺-N increased the tissue concentration of total N, P, K, and Mn. Meloidogyne spp. caused reduced dry weight of shoots and roots, with decrease in P, Mn and Fe and increase in leaf tissue Mg and Ca in highly infected plant compared to the less infected. Sweet pepper plants fertilized with lower rates of nitrogen treatments (50 ppm N and 100 ppm N) had higher Fe and Zn but with much low Mn than the treatment with more nitrogen (200 ppm N). There was high P uptake in treatments comprising of ammonium-N with the nitrification inhibitor.  Although ammonium with nitrification inhibitor (NH₄⁺-N+NI) at 200 ppm N exhibited the lowest nematode reproduction and root galling, the same treatment also had reduced shoot growth and dry weights. NH₄⁺-N+NI at 100 ppm N had higher tissue nutrient contents with reduced nematode population and higher total dry weight. The study therefore demonstrates that NH₄⁺-N fertilization with an inhibitor can reduce nematode population when plants are grown in a soil infested with the root-knot nematodes. The study also demonstrated that NH4+-N+NI showed reduction of Meloidogyne spp, better nitrogen utilization with concomitant increased plant growth and plant nutrient concentration under 100 ppm N.