NITROGEN RESPONSE OF MAIZE TO FRESH AND COMPOSTED MANURE

Growth traits and yields of maize (Zea mays) are described for varying fertilizer treatments (fresh cow manure, composted manure, inorganic NPK). Relative N-uptake is 9, 28, and 46% for compost, fresh manure and NPK, respectively. Growth rate and yields are correlated significantly with plant tissue nitrate at 30 days, which diminished in the order NPK > fresh manure > control > compost. Similarly, leaf nitrate at silking stage of maize decreases in the same order, with compost giving lowest soluble N levels. Total-N in grain at harvest does not differ significantly between the treatments, however. It is concluded that rapid early nitrogen release contributes to a high yield but elevated plant nitrate and nitrate remaining in soil after harvest are consequences which must be weighed against it. The difficulties inherent in estimating N-release from organic sources are discussed.