DIAGNOSTIC METHODS TO EVALUATE NUTRIENT STATUS OF GARLIC, ONION, AND BROCCOLI

Abstract

Field and greenhouse experiments were conducted to evaluate nitrogen status in garlic (Allium sativum L.), onion (Allium cepa L.) and broccoli (Brassica oleracea L.) under different treatments of plant density, soil moisture levels, as well as nitrogen rates and nitrogen forms. Plant samples from tops and roots were collected at different growing stages to conduct quick field tests for NO3-N and reduced-N in plant sap and total-N according to the conventional microkjeldahl method. The NO3-N sap test in fresh stems, fresh roots and dry roots of garlic were good indicators of nitrogen status and the three methods had acceptable correlation with crop yield. Fertilization with ammonium nitrate as compared to urea increased root growth and fresh weight of bulbs. In onion, only NO3-N determined in sap derived from the bulb maintained a consistent linear relationship with total-N obtained by microkjeldahl (r2=0.84). In the onion shoot the NO3-N concentration was higher than reduced-N until 130 days after sowing and in bulb the concentration of reduced-N was always higher than those of NO3-N. Sufficiency levels of NO3-N for broccoli were established in whole leaves for six growing stages as well as the sufficiency ranges for NO3-N in dry peduncles and sap derived from fresh peduncles.