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Near-Infrared Analysis of Cotton Leaves as a Guide for Nitrogen Fertilization

Dep. of Field Crops, Vegetables and Genetics, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel

Yehuda Shekel, Arie Bosak and Uzi Kafkafi

NIRA Sciences Ltd., Nehalim 49950, Israel
Sivey HaDarom Ltd., M.P. HaShikmim 79813,, Israel
Dep. of Field Crops, Vegetables and Genetics, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel

^* Corresponding author (saranga{at}agri.huji.ac.il).

Nitrate level in cotton (Gossypium hirsutum L.) leaf petioles is commonly used as a practical guide to N fertilization, especially in cases of critically low N levels. The optimization of N supply to irrigated cotton requires a reliable method for monitoring the plant's N status. The feasibility of using leaf N concentrations monitored by near-infrared analysis (NIRA) as a guide for N fertilization in irrigated cotton was examined in this study. Three field trials were conducted in three consecutive years. ]The NIRA data from fresh leaf disks were calibrated against laboratory N measurements expressed as g N kg^1–1 dry matter (R² = 0.90). Validation of the calibration showed a high correlation between NIRA estimates and laboratory data from two field trials. Dawn leaf sampling was selected for routine monitoring of plant N status. Application of NIRA-guided N fertilization was examined in the third-year trial. The NIRA-guided treatment, with only 60 kg N ha^–1, resulted in only a 7.5% lower yield (statistically nonsignificant) relative to the commercial predetermined N treatment with 150 kg N ha^–1. Yield was linearly correlated with leaf N concentration. Cotton leaf N concentration was reliably monitored by NIRA. Only 30 s are required for each N determination; using 10 samples, about 7 min are needed per plot. Once its reliability under various conditions is established, this method could be used for on-the-spot decision-making regarding N-fertilizer application in irrigated cotton.

Received for publication April 30, 1997.

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