Effect of cultivar, nitrogen level and frequency of insecticide spraying on Chinese cabbage [yield in the Philippines]

agricultural chemicals agronomic characters ammonium compounds ammonium sulphate asia botanical insecticides brassica brassica chinensis crops cruciferae cultivars dicotyledons economic plants fertilizers green vegetables insecticides nitrogen fertilizers open pollination organic compounds organic nitrogen compounds pesticides philippines physiological functions physiology plants pollination productivity profitability reproduction rhoeadales vegetable crops yields