The criteria currently used in Southern Brazil for the definition of the nitrogen (N) rate to be applied in maize are based on the soil organic matter content, the expected grain yield and the characteristics of the previous crop. Although the carbon:nitrogen (C/N) ratio is high, black oat is the most commonly used winter species antecedent to commercial summer crops. This characteristic can result in soil N immobilization, N plant deficiency and reduced grain yield in maize. Although the antecedent species are considered in the determination of the adequate N rate, little progress has been made regarding the best time for N side dressed application in maize. With the objective of evaluating the best time of the first rate of N side-dressed application in maize cultivated in succession to winter species with distinct C/N ratios, a greenhouse experiment was conducted in pots in Porto Alegre, Rio Grande do Sul, Brazil. Undisturbed columns of soil, classified as typical dystrophic Argisol (Rhodic Ultisol) were used. The treatments consisted of four systems of winter cover species (black oat, common vetch, oilseed radish and fallow) and three management forms of side-dressed N application (N applied in the growth stage V3, V5 and without N application). The experimental design was a completely randomized block, in a 4 x 3 factorial treatment combination, with three replications. Analysis of variance was performed using the F test and the treatment means were compared by Tukey's test (p < 0.05). Black oat, which has the highest C/N ratio, presented the lowest rate of mineralization and N release from its residues, while common vetch and oilseed radish have a lower C/N ratio, stimulating the mineralization and N release. Black oat preceding maize reduced the soil mineral N and N content in maize and affected the initial plant development, independent of the timing of N side-dressed application. In maize succeeding common vetch and oilseed radish, the relative leaf chlorophyll content and the dry mass production of maize in the V7 growth stage was higher in relation to that obtained in maize succeeding oat, independent of when the first rate of N was side-dressed. The obtained data indicate that it is possible to delay the first side-dressed N application in maize from V3 to V5 stage when maize is cultivated in succession to winter species with a low C/N ratio.
Zea mays; C/N ratio; winter cover species; maize plant traits; soil chemical attributes
