Effects of Paper Mill Sludge Application on Physical Properties of an Illitic Loess Slowly Swelling Soil with High Specific Surface Area and Wheat Yield in a Temperate Climate

Physical aspects of paper mill sludge application for wheat production, their relative significance and interactions were investigated in a slow swelling-shrinking soil in a temperate climate by a field experiment. Other treatments were mineral fertilizers to gauge nutritional aspects. Treatment with N and K mineral fertilizers combined and the high rate sludge application as mulch, both increased yield when low potassium kinetics otherwise caused potassium deficiency in wheat. High specific surface may increase mechanical resistance to root growth and lower nutrient uptake (K). There are two potential apposing physical aspects of sludge application on swelling-shrinkage rate and K diffusion, also root growth (low mechanical impedance) and nutrient uptake; a positive interaction by increasing soil water content in root zone versus a negative interaction by decreasing diurnal soil temperatures to suboptimal values especially before wheat heading. Low soil temperatures under sludge may become critical for shoot propagation and head density at sub-optimal temperatures of cold years for wheat growth.