UC Merced

The transferability of excess wasted organic materials, such as agricultural and forestry residues into materials like biochar and compost, to be used as a nutrient-rich organic soil amendment for food production has been viewed as an ecological approach to enhance soil ecosystem services. In this dissertation a variety of research techniques and experiments were used to investigate the effects of different locally produced biochar and also biochar dairy manure co-composts on soil hydrological properties, GHG emissions, nitrogen leaching, and crop productivity. The dissertation is divided into three main research chapters. In the first chapter, we generated moisture retention curves for seven biochar derived from wasted orchard materials e.g. almond shell, walnut shell, and almond pruning, using a mobile pyrolizer unit. More specifically, we used the water sorption film approach to determine specific surface area for the different biochar and incorporated the data into a model to assess its influence on soil moisture content. Additionally, three of the biochar (one from each feedstock) were also selected and used in two 109 days incubation studies to investigate biochar influence on soil respiration under different moisture levels. In the second chapter, numerical simulation was performed (5-years impact) on the three selected biochar to assess its impacts on soil hydrological properties and plant uptake dynamic for common cropping systems with dissimilar irrigation practices. Lastly, in the third chapter the three selected biochar were co-composted with fresh dairy manure for 45 days then used as soil amendment in a 133 day outdoor soil-tomato column study. Leaf chlorophyll content, canopy coverage, and GHG measurements were taken throughout the season as proxy for crop productivity and soil emissions as influenced by soil treatments. Results from chapter one show that walnut shell biochar has the greatest surface area while almond shell derived biochar has the most positive effect on moisture retention and soil respiration. Next, our 5-years numerical simulation shows that application of biochar at 5% enhanced water conservation by reducing seasonal soil evaporation loss and allowing for more root water uptake. However this positive effect varied between cropping systems and is substantially greater in the rainfed compared to irrigated system. In the last chapter, results from our soil-tomato study show greater positive effect on soil ecosystem services e.g. nitrogen retention and crop productivity, from biochar-dairy manure co-compost soil treatments compared to the control. However crop yield was constrained by external factors such as plant water stress.