Fallow systems are often criticized for not contributing to soil improvement, particularly when compared to practices such as cover cropping or compost application. However, in semi-arid and dryland regions, fallow continues to play an important role within cropping systems, especially when short-term crop productivity is the primary goal. Under water-limited conditions, conserving soil moisture can be more critical than increasing biological inputs in the short term, which partly explains why fallow systems often maintain strong crop performance. One of the main advantages of fallow is its ability to support moisture accumulation between cropping cycles. By leaving the field unplanted, rainfall can be stored in the soil profile and used by the following crop. In wheat–sorghum systems, this effect is not solely due to the absence of vegetation, but is strongly influenced by residue retention from previous crops. Residues from wheat and sorghum reduce evaporation, improve infiltration, and protect the soil surface, all of which contribute to improved water availability at planting.
Field observations and modeling results from semi-arid systems show that fallow-based systems can maintain relatively high sorghum yields, particularly under limited rainfall conditions. This is consistent with findings where fallow systems produced the highest sorghum yield compared to cover crop treatments, even though those systems had lower soil organic carbon levels. This indicates that yield performance in these systems is more closely tied to resource availability, especially water, than to soil carbon alone. However, it is important to recognize that this does not mean fallow systems are superior overall. While they support short-term yield, they do not contribute significantly to long-term improvements in soil organic carbon, biological activity, or soil structure. In contrast, cover crop systems increase SOC and improve soil properties over time, but may reduce sorghum yield due to competition for soil moisture, particularly when termination timing is not optimized. This highlights a key outcome observed in semi-arid systems: soil carbon gains and crop yield do not always improve together. Instead, they often represent a trade-off, where practices that enhance long-term soil health may not deliver immediate yield benefits. In this context, fallow systems remain competitive not because they improve soil quality, but because they preserve critical resources needed for crop production.
Farmers should therefore view fallow as one component within a broader management strategy, rather than as a preferred system. The decision to use fallow or integrate cover crops should depend on production goals, rainfall conditions, and management capacity. Systems that combine residue retention with improved timing of cover crop termination or planting may offer opportunities to reduce this trade-off and achieve more balanced outcomes over time.
Acknowledgment
This article is part of a project funded by the Western Sustainable Agriculture Research and Education (SARE) Program, under project number GW25-003.
