Maize residue production in the US Corn Belt: Genetics, environment, and management effects

Abstract

Crop residues play a central role in many agroecosystem processes, such as soil water evaporation and soil carbon and nitrogen cycling. However, our understanding of how management decisions and breeding impact the quantity and quality of maize [Zea mays (L.)] residue is limited. Furthermore, quantifying the historical changes in maize harvest index (HI), the fraction of above-ground biomass allocated to grain yield, can enhance our ability to estimate maize residue inputs. To better understand the historical changes in maize residue inputs and their effects on the system, the objectives of this dissertation were to i) quantify the impact of agronomic management practices on maize residue quantity and quality, ii) determine the effect of breeding on maize harvest index and residue across multiple environments, iii) explore relationships between maize residue and grain yield, and iv) estimate how carbon inputs from maize residue have changed over the last 40 years across the US Corn Belt. To achieve these objectives, a multifactorial experiment was conducted to evaluate management practices in residue characteristics, while a multilocation era experiment was conducted to determine the genetic gains. The results of these field experiments were then combined with literature data to assess potential tradeoffs between residue characteristics and grain yield and to estimate the spatial-temporal changes in residue inputs in the US Corn Belt. Among the management practices analyzed, N fertilizer rate significantly impacted the amount of residue produced and the carbon to nitrogen (CN) ratio. On the other hand, plant density had a more significant effect on the biochemical composition of the residue. Management practices that resulted in high grain yields also produced high residue quantity with low CN ratio but high lignin concentration, indicating a tradeoff in residue quality. The study also found that maize breeding increased harvest index from 0.50 to 0.57 in both, short and long-maturity hybrids. Under current growing conditions, the newer long-maturity hybrids produced 8% more residue (720 kg ha-1) than the ones from the 1980s. Due to reduced N concentration in cobs and stems, the CN ratio of residue from long-maturity hybrids increased from 52 to 57. However, breeding has resulted in a slight increase in residue quantity in short-maturity hybrids without affecting their quality. Across the US Corn Belt, maize residue carbon inputs have increased from 75 to 111 million Mg over the last 40 years, mostly due to increased productivity. However, breeding and management practices have had opposing effects on the residue CN ratio, which has remained largely unchanged in most regions. In conclusion, this study shows opportunities to manipulate residue inputs through better management practices, provides models to estimate maize residue quantity and quality, and highlights the work of breeders, agronomists, and farmers that has increased maize-based systems' production and carbon inputs.