NEAR-INFRARED ANALYSIS OF COTTON LEAVES AS A GUIDE FOR NITROGEN-FERTILIZATION

Nitrate level in cotton (Gossypium hirsutum L.) leaf petioles is commo nly 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-infr ared analysis (NIRA) as a guide for N fertilization in irrigated cotto n was examined in this study. Three field trials were conducted in thr ee consecutive years. The NIRA data from fresh leaf disks were calibra ted against laboratory N measurements expressed as g N kg(-1) dry matt er (R-2 = 0.90). Validation of the calibration showed a high correlati on between NIRA estimates and laboratory data from two field trials. D awn leaf sampling was selected for routine monitoring of plant N statu s. Application of NIRA-guided N fertilization was examined in the thir d-year trial. The NIRA-guided treatment, with only 60 kg N ha(-1), res ulted in only a 7.5% lower yield (statistically nonsignificant) relati ve to the commercial predetermined N treatment with 150 kg N ha(-1). Y ield was linearly correlated with leaf N concentration. Cotton leaf N concentration was reliably monitored by NIRA. Only 30 s are required f or each N determination; using 10 samples, about 7 min are needed per plot. Once its reliability under various conditions is established, th is method could be used for on-the-spot decision-making regarding N-fe rtilizer application in irrigated cotton.