Foliar-applied silicon may enhance fruit ripening and increase yield and nitrogen use efficiency of Arabica coffee

Nitrogen (N) is an essential element that is required in the highest amounts by the arabica coffee (Coffea arabica L.) trees. The efficiency of N fertilization in coffee could be improved by the application of silicon (Si). Thus, the objective of this study was to evaluate the effect of foliar application of soluble Si and N fertilizer on nutrition, vegetative growth, fruit ripening, bean yield, and N-use efficiency of Arabica coffee. The experiment took place from 2013 to 2017 on an Arabica coffee plantation established on a sandy clay loam Acrisol of southeastern Brazil. It was arranged in a randomized complete block design with four replications. Treatments consisted of the combination of the presence and absence of foliar application of Si with four N rates (0–300 kg N ha−1 year−1). The foliar application of Si was performed by spraying stabilized silicic acid two times per growing season (Nov. and Feb.). The source of N used was ammonium nitrate (32% N), and it was split four times (Oct.–Feb.) each year. Nitrogen fertilization reduced the stoichiometric ratios among most other nutrients and N in coffee leaves, especially by increasing plant growth and leaf N concentration. In addition, it contributed to the maintenance of plant leafiness, besides increasing the percentage of ripe fruits and coffee bean yield. Despite having only little effect on the concentration and stoichiometry of nutrients in leaves and on plant growth, Si application increased the bean yield of coffee. This was particularly so under the highest N rates, as well as the agronomic efficiency of N applied to the crop in some conditions. Silicon also reduced the percentage of dry fruits in 2017 and increased the percentage of ripe fruits (2015 and 2017). In conclusion, spraying coffee with Si in form of stabilized silicic acid potentially improves the N-use efficiency in the crop.