Crop Yields: Adaptation to Site-level Edaphic and Climate Limitations to Growth

Abstract

The Green Revolution brought about a much-needed expansion in crop yields globally in the 1970s and 1980s, particularly in developing countries. However, crop yields have plateaued or decreased over the last several decades despite planting high-yielding crop cultivars and applying abundant fertilizers. Synthetic nitrogen fertilizer applications were essential to achieve the high crop yields but produced significant environmental pollution and decreased soil health. Climate change, especially droughts, is also decreasing yields and plants are unable to adapt to its new growth environment and unpredictable disturbances. A crop needs to adapt to its growth environment to access limiting nutrients and water, and be able to protect itself from pests and pathogens without applying abundant chemicals. This shifts determining crop yield from using a photosynthesis approach, i.e., the amount of carbon fixed, to better understanding its source-sink relationships and how a plant phenologically adaptation to its growth environment. This study comprehensively reviews the different historical approaches used to improve crop yields and how yields decreased following long-term improvements in photosynthetic and nutrient-use efficiency from applying synthetic fertilizers. It introduces how knowledge of the carbon source-sink relationship or biomass distribution can address changing farming practices.This research was separated into two phases : (1) The experimental greenhouse experiment will test whether foliar plasticity is an important part of the adaptive capacity of a plant to its environment; and (2) a case study conducted in India to explore whether a plant's photosynthetic potential will be sufficient to determine the productive potential of a crop and whether it can link the site-level limits of soils and climates. In the first phase, an experimental greenhouse study was designed to test whether foliar plasticity could be an important part of the adaptive capacity of a plant to its changing environment. This was done by relating the drought tolerance of the common bean (Phaseolus vulgaris L.) to its photosynthetic efficiency. Low foliar plasticity of a crop resulted in reduced photosynthetic capacity and less biomass accumulation in droughty conditions for the common bean. Thus, foliar plasticity would be less useful in assessing a crop’s capability of adapting to climate change. The second phase of this research developed a framework to explore site-level limitations of the edaphic and micro-climatic factors on crop growth at the country-level in India. The framework's goal is to estimate a crop's theoretical maximum, potential and realistic productive capacity based on its edaphic and climatic conditions. This research explored whether a plant's photosynthetic potential will be sufficient to determine the productive potential of a crop and whether it can link the site-level limits of soils and climates. This framework uses ‘total’ crop productivity, not just the ‘product’ biomass being harvested. It estimates the maximum photosynthetic potential of a site as well as the actual productivity to determine which cultivars should be planted at a given site, especially focusing on its soil and climatic characteristics by knowing how the crop may be able to adapt to its site. This study found that the solar radiation data used to calculate maximum photosynthetic potential were insensitive to the diversity of soil types and their climatic conditions. These results also support using ‘total’ crop productivity measures, not just crop yields, when selecting plants to grow in different soil types and climatic conditions, as well as potentially being useful to determine how much fertilizer to apply to a crop.