Maize grain yield responses to plant height variability resulting from crop rotation and tillage system in a long-term experiment

Abstract

Research emphasizing slower plant growth and delayed maturity in continuous maize ( Zea mays L.), no-till (MM–NT) systems has often led to the conclusion that lower grain yields in this environment are associated with reduced plant heights. Yet prior research has shown that early-season and mature plants are not always shorter in MM–NT systems, suggesting that overall plant height may not be an accurate morphometric indicator of decreased yield in MM–NT environments. Given that plant-to-plant morpho-physiological uniformity is strongly associated with higher yield in maize, we hypothesized that greater plant height variability would provide a better agronomic explanation for yield loss in MM–NT environments than overall plant height reductions. This 14-year study primarily examined the effects of crop rotation {maize–soybean [ Glycine max (L.) Merr.] and continuous maize} and tillage system (no-till and moldboard plow) on the yield, 4-week plant population, and 4- and 8-week plant height and plant height variability of a single maize cultivar. Due to sizeable year-to-year variation, actual crop response means for the MM–NT; maize–soybean, no-till (MB–NT); and continuous maize, moldboard plow (MM–PL) treatment combinations were expressed relative to the accompanying means for the maize–soybean, moldboard plow (MB–PL) treatment. In numerous years, the MM–NT system exhibited reduced actual and relative yields and lower 4- and 8-week plant heights compared to the other treatment combinations. Both actual and relative 4- and 8-week plant height variability were rarely greatest for the MM–NT treatment, and in only a few years were actual and/or relative plant density lowest for this system. However, single-factor regression analyses between relative yield and the aforementioned relative agronomic measures revealed that a decline in relative MM–NT yield was most strongly associated with an increase in relative 4-week plant height variability. Multi-factor regression analyses between relative yield, relative 4-week plant height variability, and various weather parameters suggested that this strong inverse relationship was potentially a manifestation of (i) non-uniform germination, emergence, and early seedling growth and (ii) later-season intra-specific competition. Regression analyses between relative 4-week plant height variability and various weather parameters suggested that phenomenon (i) was potentially promoted by cool and moist or warm and dry pre-plant weather conditions while phenomenon (ii) was possibly encouraged by low precipitation and/or high temperatures during rapid stem elongation. While MM–NT systems should be managed to limit plant density reductions and minimize growth and developmental delays, increased focus should be placed on minimizing the occurrence of plant-to-plant variability in these environments.