Cropping System and Landscape Diversification to Improve Agricultural Nitrogen Cycling Under Climate Change-Driven Shifts in Precipitation.

A future warmer climate will intensify the global hydrological cycle and increase precipitation extremes, including more intense but less frequent rainfall. Shifts in seasonality and the increasingly episodic nature of rainfall will thus affect soil moisture dynamics and in turn plant productivity, including reduced crop yields in response to summer droughts or excessively wet springs in agricultural systems. Yet soil moisture is also a primary driver of terrestrial nitrogen (N) cycling, suggesting significant, but largely unknown, consequences of changing precipitation patterns for N cycling and N losses. Understanding the nature and magnitude of N-cycle process responses to climate change in agricultural systems is critical because agroecosystems are hotspots of N cycling and N losses.

Here, our aim is to synthesize current literature and establish a framework to understand how climate-change driven alterations in precipitation patterns will affect N cycling and losses in agricultural landscapes. Given the fundamental role of soil moisture in controlling plant-soil N cycling, and the characteristics of intensively-managed annual cropping systems that lead to low N retention, we expect that changes in the pattern and intensity of precipitation will exacerbate N losses. Evidence from field and landscape-scale studies show that wetter springs, drier summers, and more frequent intense rainfall events expected in many temperate regions will further decrease the coupling between plant N demand and soil N availability and increase the frequency and magnitude of pulse-driven N losses. Diversification and perennialization of cropping systems and agricultural landscapes, such as through cover cropping, more complex crop rotations, and perennial vegetation buffers, can increase N sinks and internal N cycling capacity. These strategies also promote key plant-soil linkages and soil biophysical factors that collectively buffer against more variable soil moisture regimes and could mitigate the negative consequences of changing precipitation patterns in these systems.