Analysis of coffee (Coffea arabica L.) performance in relation to radiation level and rate of nitrogen supply II. Uptake and distribution of nitrogen, leaf photosynthesis and first bean yields

Natural supply of nitrogen is often limiting coffee production. From the viewpoints of growth and biomass production, adequate nitrogen supply is important. Growing coffee under full sunlight not only enhances potential yields but also increases demands for nitrogen fertilizer, the extent of which is ill quantified. This paper provides a comprehensive analysis of N uptake and distribution, biomass production, photosynthetic characteristics of 2.5 years old trees and first bean yields of 3.5 years old coffee trees in response to four radiation treatments (30%-100% of full sun), factorially combined with four rates of nitrogen supply (0-88 g tree(-1) y(-1)). The experiment was arranged in a randomized split-split plot design and was conducted at Jimma University horticultural farm, Ethiopia, using three coffee varieties. With larger N application and higher level of radiation, more N was utilized and more biomass and yield were produced. The fertilizer-N recovery ranged from 7 to 17% and declined with larger N supply and increased with radiation level. Coffee trees provided with larger amount of N had higher amounts of N per unit leaf area, light-saturated rate of leaf photosynthesis and first bean yield compared to trees grown in low N supply and limited radiation. The relation between biomass and plant N content was conservative across coffee varieties and can be used to estimate N content from biomass or calculate required uptake to produce a given amount of biomass. Though testing of the relation for other climatic conditions is advisable, this relation can also be used in the development of process-based quantitative coffee tree growth models,. Achieving synchronies between N supply and coffee trees demand without excess or deficiency requires further investigation of options to improve the low nitrogen recovery.