Shallow Drains and Straw Mulch Alleviate Multiple Constraints to Increase Sunflower Yield on a Clay-Textured Saline Soil I. Effects of Decreased Soil Salinity, Waterlogging and End-of-Season Drought

Abstract

A well-designed drainage system can alleviate soil salinity and waterlogging, leading to increased crop yield if the drainage does not cause a water shortage late in the growing season. We conducted three field experiments with sunflower across two dry seasons in a tropical landscape to examine the effectiveness of shallow drains and mulch in overcoming these constraints. In Experiment I, four surface drains of 0.1 or 0.2 m depth spaced 1.2 or 1.8 m apart were tested along with an undrained treatment. In Experiment II, the same four drainage treatments in the main plots were split into mulch (-M and +M) sub-plots. Experiment III had four main treatments, undrained, surface drains (SD; 0.1 m deep, 1.8 m apart), subsoil drains (SSD; 0.5 m deep, 4.5 m apart) and SSD+SD each split for mulch (-M and +M) sub-plots. At vegetative emergence and at the 8-leaf stage, all plots were inundated (3–5 cm depth; ECw: 1.5–2.5 dS m–1) for 24 h before opening the drains. Drainage treatments without mulch reduced SEW30 (waterlogging index, sum of excess water within 30 cm soil depth) and soil EC1:5 at 0–15 cm, while increasing sunflower yield by 15-101 % compared to the undrained no-mulch treatment. Relative to the undrained no-mulch treatment, drains with straw mulch conserved soil water, reduced EC1:5 at 0–15 cm and increased yield in Experiments I, II and III by 12–14, 40–47 and 76–143%, respectively. There were no yield differences among the combinations of shallow drains. Although combined drains (SSD+SD) added 25–30% extra yield relative to surface drains, these have higher installation costs. Shallow surface drains at 1.2–1.8 m spacing coupled with mulch are effective options for smallholder farmers to reduce salinity, waterlogging and drought stresses, and increase yield on saline, clay soils.

Keywords: Coastal zone, Cultivar Hysun-33, SEW30, Sub-soil drain, Surface drain, Tropical environments