Critical ranges for leaf nitrogen and potassium levels in coffee fertigated at the production phase1

With the aim of establishing critical ranges for the leaf nitrogen (N) and potassium (K) levels in fertigated coffee crops under production, an experiment was carried out in the experimental area of the Sector for Coffee Cultivation of the Department of Agriculture at the Federal University of Lavras, in Brazil. Treatments consisted of five levels of fertilizer applied through fertigation: 30%, 80%, 130%, 180% and 230% of the recommended amounts of N and K for rainfed coffee grown in Minas Gerais. A randomised block design with four replications was used. Critical ranges for nutrient concentrations in the leaves were established from the results of growth characteristics (plant height and stem diameter), leaf analyses and productivity. The results obtained were: a) nitrogen (g kg-1): 32.39 to 32.40 for January/February; 33.60 to 33.61 for March/April; 27.39 to 27.42 for May/June; 24.23 to 24.24 for July/August; 26.06 to 26.09 for September/October and 26.50 to 26.51 for November/December; b ) potassium (g kg-1): 20.08 to 20.14 for January/February; 17.89 to 17.91 for March/April; 15.93 to 15.96 for May/June; 15.29 to 15.35 for July/August; 16.61 to 16.64 for September/October and 20.58 to 20.64 for November/December.

为明确生产条件下滴灌咖啡作物叶片氮（N）、钾（K）含量的临界区间，本实验于巴西拉夫拉斯联邦大学农业系咖啡栽培研究试验区开展。试验设置5组滴灌施肥处理，分别为巴西米纳斯吉拉斯州雨养咖啡推荐氮、钾施用量的30%、80%、130%、180%与230%。实验采用随机区组设计，设置4次重复。基于植株生长性状（株高、茎粗）、叶片养分分析结果与产量数据，确定了叶片养分浓度的临界范围。所得结果如下：
a) 氮（g·kg⁻¹）：1月/2月为32.39~32.40；3月/4月为33.60~33.61；5月/6月为27.39~27.42；7月/8月为24.23~24.24；9月/10月为26.06~26.09；11月/12月为26.50~26.51；
b) 钾（g·kg⁻¹）：1月/2月为20.08~20.14；3月/4月为17.89~17.91；5月/6月为15.93~15.96；7月/8月为15.29~15.35；9月/10月为16.61~16.64；11月/12月为20.58~20.64。