Effect of seed size, planting depth, and hybrid on the emergence, grain quality, and drying of maize (Zea Mays L.) in a perennial groundcover and bare soil system

Abstract

Corn (Zea mays L.) producers in the Midwestern U.S. are concerned with the effect of uneven seedling emergence on crop yield. Producers believe that just a few growing degree units (GDU’s) difference in emergence can cause interplant competition, delayed growth, and decreased yield. Many believe that this variation in emergence is due to seed size and inconsistent planting depth. Additionally, as producers are adopting new, environmentally sound cropping systems, it is crucial to understand how corn seedling emergence in these new cropping systems can affect final crop yield. Perennial ground cover and cover cropping systems are becoming more prevalent throughout the Midwestern U.S. These new systems can change soil structure, temperature, organic matter content, and nitrogen availability for seeds. Understanding the important seed characteristics and proper seed placement to ensure rapid and uniform emergence are essential in these new cropping systems. Current research reports on the effect of planting dates, depths, and GDU on delayed seedling emergence. Although these studies are beneficial, they fail to explain the possible effect of plant-to-plant competition between adjacent plants within a row when all seed is planted on the same day, at the same time. Producers understand the visual aspect of uniform emergence in their field, but its effect on cash crop yield and grain composition are not fully understood. The objectives of this study were to understand the effect of seed size and planting depth on emergence and subsequent single plant yield, and composition in a bare soil and a perennial groundcover (PGC) cropping system. To test our objectives, commercial seed from two corn hybrids (Pioneer 1197 and Blue River Hybrids 7016CNV) were resized to obtain a new seed lot with extremely uniform seed size distribution. This uniform seed size distribution was compared to the original commercially sized medium flat seed in the bag received from its respective company. The two seed sizes (resized and in the bag) for each hybrid were tested in laboratory studies and in the field in 2019 and 2020 growing seasons. Germination and vigor tests were conducted in growth chambers either as a completely random or a randomized complete block (RCB) design depending on randomization characteristics of each test. The field studies were conducted in a split-plot RCB design in both a conventional bare soil cropping system and a kentucky bluegrass (KBG) perennial ground cover (PGC) cropping system. Corn emergence in the field was flagged every 24hrs once the first seedlings emerged. Corn plants were tagged with date and time of emergence, and harvested individually. The results obtained in this study indicate that seed size, planting depth, and emergence in a PGC and bare soil system do not significantly affect corn grain yield. The seed from a smaller size distribution emerged moderately faster than commercially-sized seed received in the bag from the seed companies. However, this faster emergence did not affect final grain yield in both the PGC and bare soil cropping systems. Deeper planting depth caused a significant delay in emergence. The KBG-PGC system also delayed corn emergence, and reduced grain yield up to 50%. Delayed corn emergence caused a decrease in grain yield in both cropping systems. This yield decrease followed a quadratic or linear trend depending on the environmental factors in each growing season. Overall our study indicates that producers should be focused on planting depth and uniform seed placement, rather than seed size, to ensure consistent emergence and yield. Inconsistent planting depth causes inconsistent emergence which leads to lower grain yield. Our study also demonstrates that specific seed size fractions currently used by seed companies are justified. The sizing categories currently used by seed companies are appropriate for uniform emergence and maximum grain yield in both conventional and PGC cropping systems.