Biochar as a Beneficial Soil Amendment in Sandy Soils A long term field and greenhouse study to improve the mechanistic understanding Dissertation submitted for the award of the degree “Doctor of Natural Sciences” - Dr.rer.nat. - Presented by Ghulam Haider From, Pakistan Prepared at the Department of Plant Ecology, Faculty of Biology and Chemistry Justus-Liebig-University Giessen, Germany Giessen, 2016 The present work was carried out at the Department of Plant Ecology (Faculty 08), Justus- Liebig-University Giessen, for the award of the degree “Doctor of Natural Sciences” under the supervision of Prof. Dr. Christoph Müller. Dissertation (cumulative) submitted: October 2016 Date of disputation: December 14, 2016 Referees Prof. Dr. Christoph Müller Prof. Dr. Claudia Kammann Prof. Dr. Diedrich Steffens Prof. Dr. Hans-Werner Koyro Dedicated to my parents, family & beloved son, Saihan Haider with love and gratitude If we knew what it was we were doing, it would not be called research, would it? (Albert Einstein) Table of contents Table of contents Summary………………………………………………………………….……………. 1 Zusammenfassung………………………………………………………………………. 4 Chapter 1. Synopsis…………………………………………………………………..... 7 1.1 Introduction…………………………….…………….…………….................... 7 1.2 Literature overview………………………………………………..……............. 10 1.2.1 Biochar effects on soil properties……………………………………......... 10 1.2.2 Biochar effects on soil hydrology………………..…………….................. 11 1.2.3 Biochar effects on soil nitrogen dynamics………………..….………........ 12 1.2.4 Biochar effects on crop production…………..…………………………... 15 1.2.5 Biochar and plant nutrition……..…….….….….…………….................... 16 1.2.6 Biochar and plant ecophysiology……………….….….….….….….…….. 17 1.2.7 Biochar effects on carbon sequestration and greenhouse gasses emission 18 1.2.7.1 Carbon sequestration………….….….….….….……………………... 19 1.2.7.2 Carbon dioxide emission………………….….….….….….….………. 21 1.2.7.3 Nitrous oxide emission …………………….….….….….….….……... 22 1.2.7.4 Methane emission…………….….….….….….…….….….….……… 23 1.3 General objectives and hypothesis………………….….….….…….….….……. 24 1.4 Study site and experimental methods…………………….….…….……............ 27 Chapter 2. Biochar but not humic acid product amendment affected maize yields via improving plant-soil moisture relations………………………………………….. 34 2.1 Publication outline…………………….….….………………………………… 34 i Table of contents Chapter 3. Standard extraction methods may underestimate nitrate stocks captured by field-aged biochar…………………………….….….…….….….……… 56 3.1 Publication outline………………….….….….….….……………………........ 56 Chapter 4. Biochar reduced nitrate leaching and improved soil moisture content without yield improvements in a four-year field study............................................... 80 4.1 Manuscript outline.............................................................................................. 80 Chapter 5. General conclusions and implications........................................................ 107 Outlook: Need for future research work………………………………………………... 109 Literature cited.................................................................................................................. 111 Acknowledgements…………………………................................................................... 130 Affidavit……………………………………………………………………………….... 132 Note: Publications and their associated supplementary material pages contain their individual page numbers. ii Table of contents List of abbreviations Al Aluminum BC biochar BC Fresh biochar fresh BC Field aged biochar aged CEC Cation exchange capacity C Carbon Ca Calcium CH4 Methane CO2 Carbon dioxide Cu Copper EC Electrical conductivity EUF Electro-ultrafiltration GC Gas chromatograph GHG Greenhouse gas GHGs Greenhouse gases Gt Gigaton GWP Global warming potential HAP Humic acid product IPCC International Panel on Climate Change K Potassium KCL Potassium chloride KNO Potassium nitrate 3 M Molar Mg Magnesium MRT Mean residence time N Nitrogen Na Sodium N O Nitrous oxide 2 NH Ammonia 3 NH + Ammonium 4 NH Cl Ammonium chloride 4 NO - Nitrate 3 iii Table of contents OC Organic carbon P Phosphorous PAH Polycyclic aromatic hydrocarbons pH potentia Hydrogenii SBD Soil bulk density SOC Soil organic carbon SOM Soil organic matter TOC Total organic carbon VOCs Volatile organic compounds WHC Water holding capacity Zn Zinc iv Summary Summary The growing awareness about increaseing human population numbers and demands and the concomitant global climate change is an all-embracing subject for humankind. Therefore, it has triggered significant research efforts to meet food security and enable climate change mitigation. Biochar (BC) production and soil application has been proposed as a potential means to improve soil quality and crop production whilst serving carbon sequestration in the face of global climate change. In particular, crop water and nutrients supply is a limiting factor to crop production, even in temperate regions as climate warms, and as the frequency and severity of drought spells increases. Meanwhile, many BC studies have been conducted under greenhouse and field conditions. However, there is a dearth of investigations of BC effects on a soil-plant-atmosphere continuum, nutrient supplies and crop production under temperate field conditions. Therefore, the major aims of this thesis were to quantify the effects of BC amendment (alone or in combination with humic acid product (HAP)) on (a) soil-plant-water relations, (b) nutrients availability (both, macro- and micronutrients), (c) growth and yield of cereals under drought conditions. Furthermore, to identify the impact of BC addition on mineral nitrogen (nitrate (NO -) and ammonium (NH +)) retention and greenhouse gas (GHG) emission were 3 4 investigated. In order to accomplish these goals, laboratory, greenhouse and field studies were carried out during 2012 to 2015, using two levels of biochar amendment (15 and 30 t ha-1) in combination with two watering treatments (60 and 25 - 30% soil water holding capacity WHC in greenhouse and irrigated versus rainfed under field conditions). The WHC and greenhouse gas (GHG) emissions of BC-amended soil were carried out under controlled conditions. The impact of BC/HAP addition on water and nutrients supply was determined by monitoring the following ecophysiological parameters: water relations (leaf osmotic potential, relative water content, stomatal resistance, and leaf transpiration), leaf photosynthesis (photosystem II photochemistry) and final growth and yield of plants. The results of growth and yield improvement (as observed in the greenhouse) were tested on diverse crops under field conditions for four years. In addition, following the initial observations of greater NO - retention in BC amended soil under greenhouse study, the type 3 and strength of mineral N retention in soil, fresh and field aged biochar were investigated with different mineral N extraction methods. 1 Summary The results of preliminary greenhouse studies revealed that BC addition has the potential to enhance soil WHC and to mitigate soil GHG emissions. The increased moisture supply with BC amendments was able to maintain soil nutrient supplies under both water supply conditions, thereby increasing plant growth and biomass yields. The loading of HAP on BC had no significant effect on soil-plant-water relations, photosynthesis, and final dry matter yield. However, the results of the greenhouse study could not be transferred directly under field conditions during 2012 - 2015. In the year 2012, freshly incorporated BC increased soil moisture, caused manganese (Mn) deficiency and reduced N uptake thereby reducing grain yield of the first crop. Supplying micronutrients in addition with N fertilization (2013) did not increase N uptake but soil N content and had no significant effect on grain yield of the second crop. Interestingly a higher NO - retention was observed in topsoil (0 - 15 cm) of BC 3 amended plots since the start of the study. Furthermore, the higher NO - retention of BC amended soils was confirmed by deep (0 - 90 3 cm) soil sampling during 2014. To test the availability of the stored soil N the subsequent third crop was not supplied with N fertilizer. Unfortunately, even though N concentrations were higher in BC amended soils they were not available to plants and caused a reduction in N uptake and grain yield. In the last year of field study (2015), there was no significant effect of BC addition on N uptake or grain yield. However, a prolonged drought spell (32% less precipitation compared to 396 mm as the 30-year average precipitation) during crop growth season (April - October 2015) caused reduced soil moisture, N uptake and grain yield of the fourth crop. Contrary to the expectations from the greenhouse study, the BC application did not alleviate drought impact on grain yield of the crop under field conditions. The increased NO - retention of the BC amended soil is in strong contrast to the hypothesis 3 that there will be higher NH + retention in BC amended soil where the positive charge of 4 NH + enables sorption on negatively charged BC surfaces. The latter hypothesis could not be 4 confirmed. Instead, subsequent investigations revealed that the increase of NO - retention was 3 associated with BC particles. In addition, the binding of NO - by BC particles was so strong 3 that standard extraction methods (2 M KCl and electro-ultrafiltration (EUF)) were inefficient to extract all captured NO -. Therefore, new N extraction approaches were developed in this 3 thesis. 2