Degree Type

Thesis

Date of Award

2016

Degree Name

Master of Science

Department

Agronomy

Major

Soil Science

First Advisor

John E. Sawyer

Abstract

Winter cereal rye (Secale cereal L.), a commonly used cover crop in corn (Zea mays L.) systems has potential to scavenge soil NO3–N through a fibrous root system. The objective of this study was to quantify root and shoot biomass, C, and N partitioning in rye cover crop at the time of termination in spring. This was a one–year study conducted at a site with a no-till corn–soybean [Glycine max (L.) Merr.] rotation, rye drilled following grain crop harvest, and three N rates applied to corn (0, 135, and 225 kg N ha–1). Rye root biomass to 60-cm depth following corn and 30-cm depth following soybean was estimated using ingrowth tubes installed in the fall after rye seeding and removed at the time of rye termination in the spring. For rye following corn and soybean, 48 and 62 %, respectively, of the total root biomass was present in the top 15-cm depth. Overall, the shoot biomass, C, and N was significantly greater than for roots, with approximately two times more shoot than root material and only 33–36 % of total plant C and 17–18 % of total plant N in the root biomass. The C:N ratio of root biomass was consistently high (47–52), and at least double the shoot (16–23). With high C, low N, and high C:N ratio of the rye roots, inorganic-N from soil or degrading shoot biomass could be immobilized with root degradation and reduce potential N recycling.

Cereal rye (Secale cereal L.) cover crops (RCC) have good potential to take up residual NO3 between grain crops and reduce loss to surface waters. However, studies in Iowa have shown a 5–6% corn (Zea mays L.) yield reduction when grown following a RCC. The objective of this research was to study agronomic practices that have potential to improve corn yield in a RCC system. This study was conducted at four sites in 2013 through 2015 with corn grown in rotation with soybean [Glycine max. (L.) Merr.]. Treatments included cereal rye aerially broadcast into soybean before leaf drop and no RCC, tillage or no-till, and starter N fertilizer (34 kg N ha–1) or no starter. The aerial RCC sowing, especially with dry fall conditions the first year and planned RCC termination in the spring at 15–20 cm height, resulted in non-uniform RCC stand and low biomass and N uptake at termination (154–335 kg ha–1 and 6–14 kg N ha–1). Across site-years, V6 corn plant height and V10 sensing indexes were greater with the tilled system and starter N. Overall, corn yield was slightly reduced with the RCC (2.4%), however, tillage (3.3%) and the high N starter (1.6%) consistently increased yield. Soybean yield was not influenced by the aerial seeded RCC or the prior year treatments for corn. While the RCC generally resulted in lower corn yield, starter N and tillage did help offset that reduction and would be expected to help improve corn production in a RCC system.

Copyright Owner

Swetabh Patel

Language

en

File Format

application/pdf

File Size

87 pages

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