THE EFFECT OF COMBINED APPLICATION OF ORGANIC UREA AND FARM YARD MANURE ON THE PERFORMANCE OF SPINACH AND NITRATE CONTENT IN THE NORTHERN GUINEA SAVANNA

Abstract

Type of fertilizer is considered for influencing spinach yield and level of nitrate concentration for normal crop consumption.  This experiment investigates plant growth, yield and nitrate content of spinach with different fertilizer types and levels.  In a two location field experiment three rates of farm yard organic manure (6, 8 and 10 t ha^-1 of FYM) and three levels of N.P.K fertilizers (100:30:30, 150:30:30 and 200:30:30) were used and three combination of the two kinds of fertilizers (3t ha^-1 FYM + 90 kg N ha^-1, 4t ha^-1 FYM +  70 kg N ha^-1, and 5t ha^-1 FYM + 50 kg N ha^-1) including control (without any fertilizer) were laid out in a Randomized Complete Block Design and  replicated thrice.  The result showed that spinach treatment with urea fertilizer was superior to the treatment with farm yard manure and the control but comparable to treatment with combined application of the urea and farm yard manure. The highest and significant relative yield of 39587.92 kg ha^-1, 40222.0 kg ha^-1 and 36895.21 kg ha^-1 36354.5 kg ha^-1 were obtained from urea treatments and combined application of urea and farm yard manure at Samaru (DAC) and Shika (IAR) respectively.  While the highest farm yard manure treatments of 28792.84 kg^-1 and 27304.55 kg^-1 were produced at Samaru and Shika respectively.  However, the yield kg ha^-1 obtained with farm yard manure in both locations were higher but not significantly different from that of the control.  Nitrate concentration in the fully developed leaves samples of spinach were monitored at 4, 6 and 8 weeks after planting.  Nitrate accumulation in urea fertilized plots was observed to be directly linked to increase in nutrient concentration.   Even then the highest nitrate accumulation (1627 mg kg^-1 and 1675 mg kg^-1) which was by urea treated plants at Samaru and Shika respectively, which was a function of growth was about 55.52 – 62.54 % and 38.89 – 47.73 % higher than nitrate concentration 1001 mg kg^-1 and 1077 mg kg^-1 in FYM treated plants and 1101 mg kg^-1 and 1206 mg kg^-1 in combined application of urea and farm yard manure applied treatments in Samaru and Shika respectively.  Nitrate concentration decreased with higher farm yard manure addition to urea fertilizer and no single application of anyone fertilizer increased spinach yield along with reduced nitrate accumulation.  However, all nitrate concentration recorded were below the 3000 mg NO₃ kg^-1 limit of nitrate by the European Safety Union.