Nitrogen-molybdenum-manganese co-fertilization reduces nitrate accumulation and enhances spinach (Spinacia oleracea L.) yield and its quality

Spinach (Spinacia oleracea L.) is considered a nitrogen (N) intensive plant with high nitrate (NO3) accumulation in its leaves. The current study via a two-year field trial introduced an approach by combining N fertilization from different sources (e.g., ammonium nitrate; 33.5 % N, and urea; 48 % N) at different rates (180, and 360 kg N ha(-1)) with the foliar spraying of molybdenum (Mo) as sodium molybdate, and/or manganese (Mn) as manganese sulphate at rates of 50 and 100 mgL(-1) of each or with a mixture of Mo and Mn at rates of 50 and 50 mg L-1, respectively on growth, chemical constituents, and NO3 accumulation in spinach leaves. Our findings revealed that the highest rate of N fertilization (360 kg N ha(-1)) significantly increased most of the measured parameters e.g., plant length, fresh and dry weight plant(-1), number of leaves plant(-1), leaf area plant(-1), leaf pigments (chlorophyll a, b and carotenoids), nutrients (N, P, K, Fe, Mn, Zn), total soluble carbohydrates, protein content, net assimilation rate, and NO3 accumulation, but decreased leaf area ratio and relative growth rate. Moreover, plants received urea-N fertilizer gave the highest values of all previous attributes when compared with ammonium nitrate -N fertilizers, and the lowest values of NO3 accumulation. The co-fertilization of N-Mo-Mn gave the highest values in all studied attributes and the lowest NO3 accumulation. The best treatment was recorded under the treatment of 360 kg N-urea ha(-1) in parallel with the combined foliar application of Mo and Mn (50 + 50 mg L-1). Our findings proposed that the co-fertilization of N-Mo-Mn could enhance spinach yield and its quality, while reducing NO3 accumulation in leaves, resulting agronomical, environmental and economic benefits. (C) 2021 The Author(s). Published by Elsevier B.V. on behalf of King Saud University.