Least limiting water range of the soil seedbed for long-term tillage and cropping systems in the central Great Plains, USA

Integration of dynamic soil physical properties using the least limiting water range (LLWR) approach may allow a better understanding of soil-crop relationships in tillage and cropping systems, particularly in regions with limited precipitation and low soil organic matter content. We determined the LLWR for long-term tillage and cropping system experiments on an Argiustoll in the central U.S. Great Plains. The tillage (46 years) experiment consisted of wheat (Triticum aestivum L.)-sorghum [Sorghum bicolor (L.) Moench]-fallow (WSF) rotation under conventional tillage (CT), reduced tillage (RT) and no-tillage (NT), while the cropping system (35 years) experiment consisted of wheat-fallow (WF), WSF and continuous wheat (WW) rotations managed under RT and NT. Soil water retention curves, penetration resistance curves and bulk density were determined for the 0 to 5 cm and 5 to 10 cm depths to compute the LLWR. Mean LLWR did not differ among tillage systems for the 0 to 5 cm depth, but it was higher in RT and CT than in NT for the 5 to 10 cm depth. Mean LLWR was higher for WW than for WSF and WF in RT at both depths, but it did not differ in NT. Across cropping systems, LLWR in RT was greater than in NT by 1.2 times for the 0 to 5 cm and by 4.7 times for the 5 to 10 cm depth. Analysis of the upper and lower limits of the LLWR suggested that aeration and penetration resistance were plant-growth limiting factors in both experiments. Both tillage and cropping systems were associated with a narrow LLWR, which may reflect the limited water availability in this semiarid region. Overall, the LLWR was a useful indicator of the soil physical condition for plant growth under these long-term tillage and cropping systems and indicated that RT may produce the best soil seedbed in the central Great Plains.