Solubility and Plant Availability of Nutrients as Affected by FGD Gypsum and Glyphosate Application under Different Redox Conditions

摘要

High production agricultural systems require large inputs of fertilizers and pesticides to increase yields. In the Midwest USA, corn growth and yields may be affected by periodic saturation due to oxygen deficiency in the rhizosphere of waterlogged soils, resulting in root injury and some cell death. The objective of this study was to examine the effects of soil surface application of FGD gypsum and foliar application of a commercial form of the herbicide glyphosate on soil nutrient speciation and nutrient uptake by corn under different drainage conditions: free drainage and a perched water table. An experiment was designed in order to evaluate the changes in solubility of soil nutrients and redox sensitive nutrients, in a soil subjected to a perched water table. Four different treatments were evaluated under two different drainage conditions: a) freely drained, and b) perched water table. Treatments applied included: 1) control, 2) FGD gypsum, 3) glyphosate, and 4) FGD gypsum+glyphosate. The soilused was the silty clay loam A horizon of a Toronto-Millbrook complex. Three replicates of each treatment were conducted in 7.5-liter buckets filled with 7.75 kg of soil with a bulk density of approximately 1.1 g cm'3. Buckets for perched water table conditions were adapted with a copper brass nipple at the bottom for controlling the water table, and additionally, four platinum-copper redox sensors (two at 7 cm and two at 12 cm below the soil surface), and a ceramic cup covered with a septum for soil solution sampling 9 cm below the soil surface were added to allow monitoring of redox potential and to collect water samples. Gypsum was surface applied after planting at a rate of 1000 kg ha"1 and Roundup Weather-MAX was foliar applied at growth stage V-3at a rate of 2.338 L ha'1. Following herbicide application, the water table was held constant at -5 cm below the soil surface for the rest of the experiment. Soil solution samples were collected at 1, 3, 8, 16 and 25 days after saturation. At day 25, plants were cut, roots were washed and stored for measurement, and soil samples were taken for further analyses.