Establishment of lettuce critical nitrogen dilution curves based on total dry matter, total leaf area and leaf area duration

Abstract

ABSTRACT Considering the environmental issues linked to over fertilization, optimizing N fertilizer use is crucial for sustainable agriculture. Assessing the crop N status through calculating the N nutrition index (NNI) on the basis of critical N concentration (Nc) concept could help determine the minimum amount of N fertilizer to ensure maximum crop production. The present study aimed to develop, validate and compare three new critical N dilution curves (CNDCs) on the basis of lettuce total dry matter (TDM), total leaf area (TLA) and leaf area duration (LAD). Greenhouse experiments were conducted with six N application rates at the University of Tehran, Iran. Aboveground TDM, TLA and N concentration were measured at weekly intervals during the lettuce growth cycle. Relationships between Nc and TDM, TLA and LAD were described by three power functions (%Nc = 4.84 TDM−0.11, %Nc = 7.73 TLA−0.11, %Nc = 9.40 LAD−0.11). Furthermore, an allometric relationship between lettuce TDM and TLA (TLA = 0.75 TDM0.34) was obtained. The developed TLA and LAD-based CNDCs have the benefit of being non-destructive if TLA could be measured by portable devices. Overall, the CNDCs developed in the present research could provide accurate N status diagnosis for lettuce N management under greenhouse conditions.