Abstract
Soil health is a necessity for a sustainable future from food security to ecosystem health. Nearly 38% of the earth’s land surface is farmed, meaning agriculture has an enormous role in maintaining the capacity of soil to sustain plants, animals, and humans. We are faced with the challenge of increasing production on this land to support current and projected population growth without jeopardizing the future by degrading our soil. This challenge is exacerbated by climate change and instability leading to changes in weather patterns, temperature, and precipitation regimes worldwide. In Idaho, producers face challenges such as drier summers, higher temperatures, and extreme precipitation, leading to increased demand for limited water resources. As such, there is a clear need to investigate growing strategies that are resilient to water stress and advantageous to soil health. The production of barley and nitrogen-fixing pulse crops such as lentils and peas, often in rotation, is already a staple of Idaho agriculture. This research investigates the effects of growing barley and pulse crops together simultaneously (intercropping) on soil health, focusing specifically on nutrient status and soil microbial communities. To understand the role water limitation will play in intercropping, soil health was measured under full irrigation and deficit irrigation conditions.
We demonstrated that complementary root strategies in barley/pulse intercropping allow a more complete use of water and nitrogen in the soil profile, as barley accesses deeper resources than pulse crops. The reduced competition to barley led to improved barley yields under intercropping, while pulse crop yields were reduced. Under water stress, these yield dynamics were exacerbated, likely because reliance on the unique resource niche accessed by each crop was more apparent when water was limiting. Intercropping additionally altered the soil microbial community, overall increasing diversity as compared to barley grown alone. This shift was especially apparent for barley/lentil intercropping.
The response of barley to intercropping with peas as compared to lentils was not identical. Intercropping barley with pea resulted in greater relative yields than intercropping with lentil, likely due to increased nutrient availability. Stable isotope tracing of pulse crop nutrient allocation suggests that peas release a greater proportion of fixed carbon and nitrogen to the soil than lentils, increasing access to companion crops and microbes. Further, we demonstrated the short-term connectivity of barley and pulse crops grown together, with nitrogen fixed by pulse crops detected in the roots of companion barley crops within the range of several days.
Significant changes in soil health metrics observed after a single growing season are a positive indication that intercropping barley and pulse crops is a strategy that could benefit producers. Data obtained from subsequent growing seasons will further clarify the longer-term effects of intercropping and water availability on soil nutrients, microbial community, and productivity. This work can help to inform management decisions such as inputs and crop selection for producers aiming to employ diverse cropping strategies and improve soil health.