Sustainable Intensification and Climate Resilience: Cover Crops, Soil Improvement, and Drought

Open Access
Author:
Hunter, Mitchell Clayton
Graduate Program:
Agronomy
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
May 17, 2018
Committee Members:
  • Dr. David Mortensen, Dissertation Advisor
  • Dr. David Mortensen, Committee Chair
  • Dr. David Eissenstat, Committee Member
  • Dr. Armen Kemanian, Committee Member
  • Dr. Jason Kaye, Outside Member
  • Dr. Meagan Schipanski, Special Member
Keywords:
  • sustainable intensification
  • cover crops
  • drought
  • climate change
  • food demand
  • soil health
  • reduced tillage
  • climate resilience
  • cover crop mixtures
  • agriculture
  • agronomy
  • greenhouse gas emissions
  • Mississippi River Phosphorus
  • maize
  • soybean
  • wheat
  • cereal rye
  • red clover
  • no-till
  • soil improvement
  • plant-available water
  • infiltration rate
  • available water capacity
Abstract:
This dissertation evaluates the potential for cover crops and soil improvement to contribute to sustainable intensification and climate resilience. Chapter 2 provides balanced, quantitative targets for the sustainable intensification of agriculture. Updated food demand projections showed that demand will increase only 26-68% between 2014 and 2050, in contrast to the prevailing narrative that demand will double. At the same time, a review of published goals for agricultural greenhouse gas emissions and nutrient losses to water bodies showed that agricultural pollution must decrease rapidly to maintain ecosystem integrity. Chapter 3 analyzes the effects of multi-species cover crop mixtures on the mean levels and spatiotemporal stability of cash crop yield and soil N supply in an organically-managed three-year rotation of maize (Zea mays L.), soybean (Glycine max L.), and wheat (Triticum aestivum L.) in central Pennsylvania. Nitrogen-mineralizing cover crops increased soil N supply and maize yield. Cover crops did not affect soybean or wheat yield. A novel stability metric showed that the stability of soil N supply was a strong predictor of the stability of maize yield (R2 = 0.849). Chapter 4 evaluates the potential for cover crops to mitigate drought stress. Rainout shelters were deployed in maize grown following functionally-diverse cover crops over two growing seasons. Drought reduced maize yield by 23.2%, while the cereal rye (Secale cereale L.) cover crop reduced yield by 33.6%, likely due to N immobilization. Red clover (Trifolium pratense L.) resulted in high and stable maize yield across years and drought conditions. Cover crop N supply was critical for canopy formation and chlorophyll content, enhancing radiation interception and use efficiency. Chapter 5 evaluates the drought-mitigating effects of long-term soil improvement using the Cycles cropping system model. Maize yield under historical and future climate conditions was simulated in soils parameterized based on the results of a long-term (49-year) field study of four different soil disturbance regimes, which led to substantial differences in infiltration rate (IR) and available water capacity (AWC). Overall, reduced soil disturbance increased simulated yield by up to 13.3%. Improved AWC increased yield more than improved IR (8.52% v. 3.33%).