Rotation Design: A Critical Factor for Sustainable Crop Production in a Semiarid Climate: A Review

Abstract

The concept of “fallow” has been a prominent management tactic in semiarid regions of the world, enabling producers to compensate for low precipitation. However, fallow phases lead to soil degradation. For example, winter wheat (Triticum aestivum L.)-fallow with tillage has been used for decades in the semiarid steppe of the United States; organic matter levels in soils have declined almost 60%. Thus, producers in this region are concerned about the future sustainability of this rotation. No-till practices, however, improve water relations such that more crops can be added to the winter wheat-fallow rotation. This change in cropping patterns has led producers to seek cropping systems that are economically viable, restore soil health, improve resource-use-efficiency, and reduce the need for external inputs such as pesticides and fertilizers. Long-term rotation studies in the steppe show that continuous cropping with no-till can accrue these four goals. However, with water supply often being limiting, rotation design is critical for success with continuous cropping. Designing rotations in a cycle-of-four with a diversity of crops, increases net returns four-fold while reducing the cost of weed management 50% compared with conventional systems. Continuous cropping for 12 years increased soil organic carbon by 37% and nitrogen by 20% in the top 5 cm of soil, and also improved soil porosity and aggregate stability. Consequently, soil productivity has increased two-fold. Also, the cycle-of-four design provides a crop niche for legumes in this semiarid climate, which further enhances soil function. Some crops improve water-use-efficiency of the following crops by 20–35%, thus ameliorating the impact of low precipitation. Continuous cropping with no-till has initiated a spiral of soil regeneration.