Combinations of tall standing and horizontal residue affect soil water dynamics in rainfed conservation agriculture systems

• Large amounts of horizontal residue reduced infiltration with light rainfall events.
• Tall-cut crop residues increased rainfall infiltration in the residue row.
• Tall-cut crop residues increased soil water content and depth in the residue row.
• A combination of tall standing and horizontal residue maximised soil water content.

Residue retention is a key component of modern conservation agriculture systems. However, conflicting evidence exists on the role of residue and its architecture on the capture of rainfall and subsequent water storage in the soil in rainfed environments. Experiments were conducted in 2010 and 2011, on a sandy soil, to investigate the effect of crop residue height and architecture on the capture of rainfall and spatial variability of soil water across the standing-residue rows. We hypothesised that: (1) high residue rates, particularly horizontal residue, prevent water reaching the ground during small rainfall events, but maximise soil water retention during larger rainfall events; and (2) tall standing-residue increases the capture of rainfall and reduces evaporation from the soil surface, but increases spatial variability of soil water. To test this we investigated the effect of combinations of vertical (0–0.3 m) and horizontal (0–4.0 t ha−1) residues on water capture (using simulated rainfall, sprinkler irrigation and rainfall events), and the quantity and spatial distribution of water stored in the soil. The quantity of water intercepted by residue in the inter-row position increased with rate of horizontal residue and standing-residue height. However, the quantity of stored water concurrently increased under and adjacent to the standing-residue row, suggesting that some of this ‘lost’ water was intercepted by the high-cut residue, much of which infiltrated deeper into the soil, where it was less prone to evaporation. The quantity of stored soil water increased with increasing residue cut-height and horizontal residue, with bare soil having the least water. Most soil water was stored with straw cut high (0.25–0.3 m) in combination with at least 2 t ha−1 horizontal residue, with soil directly under the standing straw row having the most water. Thus, retaining tall standing-residue in combination with horizontal residues can increase soil water capture in the no-till system.