Estudo de danificações mecânicas em sementes de milho (Zea mays L.).

Abstract

In Brazil, the waste of seeds and grains of com, caused mainly by harvesting, mechanical thrashing, improvement, and subsequent processes, are high and cause economic damages for the country. Thus, the objective of this dissertation is to evaluate the effects of mechanical damages on seeds of two kinds of corn {lea mays L.) during mechanical thrashing; the first experiment (2001/2002) was done with the Cruzeta and Sertanejo varieties, throshed at a humidity proportion of 10%, at rotations of 520, 600 and 700 rpm, respectively. After the thrashing, the damage done to the seeds was evaluated after they passed through the various phases of the improvement unit (UBS); and in another experiment (2002/2003) with the Sertanejo variety, picked up with the humidity proportion of 20%, 16%, 14% and 12%, submitted to mechanical thrashing in the same machine and rotations as the first experiment. In processes of mechanical thrashing, the rotations employed in the thrashing machine were obtained by varying the tractor acceleration to which the machine was attached. The seeds gathered after each operation were stored in appropriate containers and then taken to the Laboratorio de Pre-Processamento de Produtos Vegetais do DEAg/UFCG for evaluation of loss percentage, damage (broken or cracked seeds) germination and physical purity. The statistical delineation adopted was entirely combined with the treatments distributed in a factorial scheme. The results of the analyses done within each working condition led to the following conclusions: the seeds which had 14% of humidity presented a higher percentage of purity, germination and a lower index of mechanical damage; the harmful effect of the impact on the seed quality becomes more evident with the rise not only in the speed of the thrashing cylinder but also in the height from which they are thrown; the Cruzeta variety was more resistant to the impacts caused by the thrashing and improvement, as well as a greater viability (germination), but the losses at the moment of thrashing were less with the Sertanejo variety; the 600 rpm rotation proved to be more advisable for the thrashing of the Cruzeta and Sertanejo corn.