Relations between growth, N level, NH4-N ratio of fertilizer, climatic variables, harvest time and tipburn of cos lettuce grown under the cold glasshouse

Abstract

A study was conducted to analyze relations between growth, N level, NH4-N ratio, climatic variables, harvest time and tipburn, and also the effects of N level, NH4-N ratio of fertilizer and climatic variables on plant growth, yield and tipburn in cos lettuce grown in an unheated glasshouse in 2008-2009 winter-early spring growing period. Results showed that effects of applied N and NH4-N ratios on plant growth, yield and tipburn were not statistically significant, but data suggested that lettuce yield tended to decline with the increased N and increased NH4-N ratio of fertilizer. Moreover, of all the variables evaluated for internal tipburn incidence, the night relative humidity had the highest correlation coefficient (r = 0.910, p<0.01) while for the external tipburn incidence, soil K/Ca ratio had the highest correlation coefficient (r = 0.738, p<0.01), but these two variables were not the only variables correlated with the tipburn in cos lettuce. Our results suggest that, by statistical means, complex contributions of many variables had effect on tipburn of cos lettuce.