Effects of Early Stresses On Plant-to-Plant Variability and Grain Yield in Maize.

Stress tolerance has been proposed to be the main way to achieve future yield increases in maize (Zea mays L.), but it is not well understood how stresses during early phases of development impact yield. Variability among plants in a stand of genetically identical maize plants increases when the plants are exposed to stress and plant-to-plant variability (PPV) is negatively associated with grain yield. The objective of this study was to quantify the effect of early stresses on PPV in dry matter and grain yield. We postulate (i) that early stresses are positively associated PPV in dry matter, (ii) that reductions in crop yield are attributable, in part, to the negative association between plant-to-plant variability and yield, and (iii) that effects of plant-to-plant variability on grain yield are modulated by the level of stress throughout the remainder of the life cycle. To address these hypotheses, a study was carried out using a split-plot design with early stresses as main treatments and N application at the 12 leaftip stage as sub treatments. Main treatments consisted of a combination of winter-wheat competition, starter N fertilization, and maize plant density until the 12-leaftip stage of maize. The split treatments were 0 and 150 kg/ha N applied at the 12-leaf stage. Results showed that early stresses affected PPV.  Grain yield was affected both by early stress and N application after the 12-leaf stage. Although the interaction between early stress and late N application was not statistically significant, late N application tended to diminish the effect of early stress on grain yield.