Effects of soil type, rainfall, straw mulch, and fertilizer on semi-arid vegetation establishment, growth and diversity

Revegetation in arid and semi-arid environments often involves strategies to augment soil properties to promote plant establishment and growth while ameliorating the effects of variable rainfall. A southern Arizona USA greenhouse experiment evaluated the impact of rainfall, common amendments, and three soil types on grassland revegetation. Based on rainfall data from a nearby semi-arid site, three irrigation levels were used to simulate the rainfall of a dry (275. mm), average (320. mm), and wet (555. mm) year. The three amendments were bare soil, straw (4.5. Mg/ha with a tackifier), and straw plus slow-release fertilizer (7-2-3 NPK, 3.4. Mg/ha). Three field-collected soil types were used: a very gravely sand, a very gravelly loamy sand, and a gravelly sandy loam. Four seed mixes were used as a blocking factor. There was a significant interaction between amendment and soil type, soil type and rainfall scenario, as well as amendment and rainfall scenario. Straw alone or with fertilizer increased aboveground biomass (72-177% increase) on the gravelly sandy loam, and very gravelly loamy sand soils but decreased biomass on the very gravely sand (13% and 54%). Straw with fertilizer did not change species richness and diversity significantly, but it resulted in a greater than 50% decline in establishment for all soil types. Straw alone significantly increased the aboveground biomass only in low (205%) and average rainfall scenarios (40%), but not when rainfall was high (11%). The specific site conditions ultimately determine which practices will result in successful revegetation.