Date of Graduation

5-2022

Document Type

Thesis

Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Trenton Roberts

Committee Member

Matthew Bertucci

Second Committee Member

Mary Savin

Third Committee Member

Jeremy Ross

Keywords

Biomass, Cardinal temperatures, Cover crop, Growing degree day, Thermal units

Abstract

Including cover crops in agricultural production systems is an important management practice. Cover cropping can improve soil health, increase plant-available nitrogen (N), provide surface residue to prevent erosional soil loss, increase water infiltration, and increase weed suppression. Cover crops growth can be predicted using thermal days or growing degree days [GDD] similar to commodity crops such as corn (Zea mays L.) or rice (Oryza sativa). Growing degree day calculations are a well-known tool to predict crop growth stage or development stage and can be adapted for use in any plant species, including cover crops. Identifying and developing the relationship between cover crop growth and GDD parameters could improve the estimation of biomass production of cover crops. Generally, GDD is the summation of daily thermal units [DTU], and DTU can be calculated using several different methods, but all use species-specific cardinal temperatures. There are very basic equations to determine DTU accumulation that only account for the average daily temperature and the species base temperature. There are also very complex and more realistic equations that account for the other cardinal temperatures (optimum and maximum) to help improve the precision of the DTU and ultimately the GDD estimation. The cardinal temperatures are not well defined in the literature for most cover crop species, leading to a less accurate calculation of GDD for many of these species. To have a more accurate and realistic estimation of plant growth, these cardinal temperatures for each cover crop species are necessary and represent the first objective of this research. The second objective of this study is to estimate cover crop biomass accumulation and total N uptake based on GDD for Arkansas production systems. The first step to achieve this goal was a growth chamber experiment used to determine the cardinal temperatures for eight cover crops species, including Austrian winter pea [AWP] (Pisum sativum), balansa clover (Trifolium michelianum), crimson clover (Trifolium incarnatum), common vetch (Vicia sativa), hairy vetch (Vicia villosa), barley (Hordeum vulgare), black-seeded oats (Avena sativa), and cereal rye (Secale cereale). Identifying the cardinal temperatures will allow the use of more complex, plant-growth prediction models. The data collected from the growth chamber experiment was regressed to estimate the cardinal temperatures for each species. The estimated base, optimum, and maximum temperatures for each species were, respectively, -0.1, 25.4, and 40.2 °C for AWP, 3.4, 26.6, and 31.5 °C for balansa clover, 0.4, 18.4, and 47.4 °C for barley, 3.4, 17.8, and 44.6 °C for black-seeded oat, -4.5, 24.8, and 36.4 °C for cereal rye, 1.3, 23.7, and 33.2 °C for common vetch, 3.9, 26.6, and 39.1 °C for crimson clover, and 2.8, 26.3, and 34.7 °C for hairy vetch. Many of these temperatures were not defined previously in the literature and add valuable information regarding the growth of these cover crop species. The successful identification of these cardinal temperatures supported the work in the second objective, which is a field experiment designed to identify a possible relationship between biomass accumulation and total N uptake based on GDD accumulation. The experiment was conducted at the Rohwer Research Station, near Watson, Pine Tree Research Station, near Colt, and Vegetable Research Station, near Kibler, in Arkansas to provide differences in climate and rate of GDD accumulation using the same eight cover crop species. Aboveground biomass production and total N uptake were regressed as a function of GDD for each cover crop treatment. The result was a three-way interaction among cover crop species, GDD, and location for total N and aboveground biomass accumulation. A similar increase in aboveground biomass accumulation and N uptake was observed across all locations. The growth rate was higher closer to termination since warmer temperatures allow each species to accumulate more GDD. This research will assist in developing decision aid tools that producers can use to determine ideal cover crop termination dates and the potential N accumulation in cover crop biomass.

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