Effect of planting density on green ear yield of maize cultivars bred in different periods

Corn cultivation in the Northeast region of Brazil is characterized by a great diversity of production systems, ranging from large companies (modem cultivars and relatively high planting densities) to small farms (family agriculture, traditional cultivars, and low planting densities). In the present work we evaluated the effects of planting density (30; 40; 50; 60; or 70 thousand plants ha(-1) - TPH) on green ear yield of cultivars Centralmex (traditional) and AG 510 (hybrid). Different densities were achieved by maintaining 1.0 m between rows and varying the spacing between pits, within the row. Cultivars and planting densities were combined in a factorial scheme, arranged in a random block design with four replicates and four 6 in long row plots. The number of green ears increased with density in both cultivars, but in a significantly more intense pace in cultivar AG 510. Cultivar AG-510 (14.9 t ha(-1) on average, maximum yield at 58 TPH) yielded significantly more unhusked green ears than cultivar Centralmex (13.6 t ha(-1) on average, maximum at 61 TPH). Marketable green ear yield increased with density in both cultivars, but more intensively in cultivar AG 510, which significantly out yielded cultivar Centralmex from 43 TPH ahead. The difference between cultivars at the planting density of 70 TPH was 14.4 t ha(-1). There was no response of cultivar Centralmex in number of marketable husked green ears, while cultivar AG 510 increased yield with planting density. The difference between both cultivars started being significant at 38 TPH. Husked ear length decreased linearly and similarly in both cultivars as planting density increased. Planting density did not influence plant and ear height, and cultivar Centralmex was superior in both characteristics at all planting densities. There was no effect of cultivars on stalk diameter and root system biomass. Both characteristics decreased linearly as planting density increased.