Omondi, J.O., French Associates Institute for Agriculture and Biotechnology of Drylands, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel, Gilat Research Center, Agricultural Research Organization, Gilat, Israel; Lazarovitch, N., French Associates Institute for Agriculture and Biotechnology of Drylands, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel; Rachmilevitch, S., French Associates Institute for Agriculture and Biotechnology of Drylands, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel;

Cassava (M. esculenta Crantz), feeding countless people and attracting markets worldwide, is a model for traditional crops that need physiology-based fertigation (fertilization through irrigation) standards in intensive cultivation. Hence, we studied the effects of 10 to 200 mg L-1 nitrogen (N) fertigation on growth and yields of cassava and targeted alterations in their photosynthetic, transpiration, and carbohydrate management. We found that increasing irrigation N from 10 to 70 mg L-1 increased cassava’s photosynthesis and transpiration but supported only the canopy’s growth. At 100 mg N L-1 cassava reached a threshold of sugar in leaves (∼47 mg g-1), began to accumulate starch and supported higher yields. Yet, at 200 mg N L-1, the canopy became too demanding and plants had to restrain transpiration, reduce photosynthesis, decrease carbohydrates, and finally lower yields. We concluded that the phases of cassava response to nitrogen are: 1) growth that does not support yields at low N, 2) productive N application, and 3) excessive use of N. Yet traditional leaf mineral analyses fail to exhibit these responses, and therefore we propose a simple and inexpensive carbohydrate measurement to guide a precise use of N. © Copyright © 2019 Omondi, Lazarovitch, Rachmilevitch, Yermiyahu and Sperling.