Characterizing Soil Acidity and Aluminum Toxicity in the Palouse Using a Proton Balance and Ion-Exchange Membranes.

Soil acidification (SA) from repeated ammonia-based fertilizers is severely impacting soil chemistry/biology and crop quality, leading to significant yield reductions.  Results confirm stratified soil acidity layers for direct-seed (DS) systems, long-term soil pH trends nearing critical threshold values beyond recovery for various cropping systems, and increased aluminum ion (Al⁺³) and other Al-species activity concomitant with the rapid pH declines.  Unless SA mechanisms are better understood to ameliorate with lime and complementary management practices, sustainability of Palouse cropping systems is threaten from Al phytotoxicity, decreased soil microbial diversity, changes in nutrient cycling, and reduced organic matter decomposition rates.

Instead of relying on a pH meter to measure long-term changes in soil chemistry in determining corrective measures, ion-exchange membranes and a proton balance method of tracking H⁺ ions from system cycling of C, N, and S are employed.  Our overall goal is to predict SA rates of various cropping systems (no-tillage, perennial-based and organic farming) using a proton balance and soil characterization data to establish appropriate management practices.  Expected outcomes include (1) prediction of SA rates for different cropping systems using a proton balance; (2) knowledge of nutrient availability and Al toxicity in different cropping systems where SA is occurring; (3) identify relationships among base saturation, soil buffering capacity, and SA rates; and (4) determination of best management practices for ameliorating SA and Al phytotoxicity.