Hydrolytic Amino Acids Employed as a Novel Organic Nitrogen Source for the Preparation of PGPF-Containing Bio-Organic Fertilizer for Plant Growth Promotion and Characterization of Substance Transformation during BOF Production

RESEARCH ARTICLE Hydrolytic Amino Acids Employed as a Novel Organic Nitrogen Source for the Preparation of PGPF-Containing Bio-Organic Fertilizer for Plant Growth Promotion and Characterization of Substance Transformation during BOF Production Fengge Zhang1,2☯, Xiaohui Meng1☯, Chenglong Feng1, Wei Ran1,3, Guanghui Yu1,3, Yingjun Zhang2, Qirong Shen1,3* 1 National Engineering Research Center for Organic-based Fertilizers, Nanjing Agricultural University, Nanjing, 210095, China, 2 Grassland& Environmental Engineering Lab, Nanjing Agricultural University, Nanjing, 210095, China, 3 Jiangsu Collaborative Innovation Center for Solid Organic Waste Utilization, Nanjing Agricultural University, Nanjing, 210095, China OPEN ACCESS Citation: Zhang F, Meng X, Feng C, Ran W, Yu G, Zhang Y, et al. (2016) Hydrolytic Amino Acids Employed as a Novel Organic Nitrogen Source for the Preparation of PGPF-Containing Bio-Organic Fertilizer for Plant Growth Promotion and Characterization of Substance Transformation during BOF Production. PLoS ONE 11(3): e0149447. doi:10.1371/journal.pone.0149447 Editor: Jingdong Mao, Old Dominion Univ., UNITED STATES Received: October 4, 2015 Accepted: January 31, 2016 Published: March 14, 2016 Copyright: © 2016 Zhang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Funding: This work was financially supported by 973 project (2015CB150506), Innovative Research Team Development Plan of the Ministry of Education of China (IRT1256), and the Priority Academic Program Development (PAPD) of Jiangsu Higher Education Institutions. ☯ These authors contributed equally to this work. * Abstract Opportunity costs seriously limit the large-scale production of bio-organic fertilizers (BOFs) both in China and internationally. This study addresses the utilization of amino acids resulting from the acidic hydrolysis of pig corpses as organic nitrogen sources to increase the density of TrichodermaharzianumT-E5 (a typical plant growth-promoting fungi, PGPF). This results in a novel, economical, highly efficient and environmentally friendly BOF product. Fluorescence excitation-emission matrix (EEM) spectroscopy combined with fluorescence regional integration (FRI) was employed to monitor compost maturity levels, while pot experiments were utilized to test the effects of this novel BOF on plant growth. An optimization experiment, based on response surface methodologies (RSMs), showed that a maximum T-E5 population (3.72 × 108 ITS copies g−1) was obtained from a mixture of 65.17% cattle manure compost (W/W), 19.33% maggot manure (W/W), 15.50% (V/W)hydrolytic amino acid solution and 4.69% (V/W) inoculum at 28.7°C after a 14 day secondary solid fermentation. Spectroscopy analysis revealed that the compost transformation process involved the degradation of protein-like substances and the formation of fulvic-like and humic-like substances. FRI parameters (PI, n, PII, n, PIII, n and PV, n) were used to characterize the degree of compost maturity. The BOF resulted in significantly higher increased chlorophyll content, shoot length, and shoot and root dry weights of three vegetables (cucumber, tomato and pepper) by 9.9%~22.4%, 22.9%~58.5%, 31.0%~84.9%, and 24.2% ~34.1%, respectively. In summary, this study presents an operational means of increasing PGPF T-E5 populations in BOF to promote plant growth with a concomitant reduction in PLOS ONE | DOI:10.1371/journal.pone.0149447 March 14, 2016 1 / 17 Preparation of PGPF-Containing BOF by Hydrolytic Amino Acids and Compost Maturity Characterization Competing Interests: The authors have declared that no competing interests exist. We also had no Competing Interests to the patent (An amino acid compound made from waste proteins of dead pigs by acid hydrolysis, China patent: ZL201410042218.3) relating to material pertinent to this article. This does not alter our adherence to PLOS ONE policies on sharing data and materials. production cost. In addition, a BOF compost maturity assessment using fluorescence EEM spectroscopy and FRI ensured its safe field application. Introduction Trichoderma species exhibit extremely high levels of ecological adaptability through their symbiotic colonization of plants and saprophytic existence in all soil types. Their capacity to improve plant growth and promote health in agricultural systems has been well documented. Recognized as plant growth-promoting fungi (PGPF) [1], Trichoderma form mutualistic relationships with many crops [2, 3]and have been widely implemented as biocontrol agents for protection against numerous soil-borne plant diseases [4–6]. However, successful biocontrol requires the formulation of carriers that ensure Trichoderma survival and maintenance of a significant population in soil. Several inexpensive agricultural wastes (e.g. animal manure and agricultural industry byproducts [7–9]) have been recognized as feasible organic carriers of many bio-agents. Manure addition to soil is known to improve soil fertility and positively influence crop quality and yields [10]. Bio-organic fertilizers (BOFs) that contain Trichoderma spp. and animal manure have been shown to promote plant growth and control Fusarium wilt in cucumber plants [5, 11, 12, 13]. In previous studies and through commercial BOF production, defatted rapeseed meal has been used as an organic nitrogen source during secondary co-solid-fermentation with manure compost for BOF production [12, 14]. While defatted rapeseed meal is used as animal feed, marginal costs for BOF production exceed marginal revenues. This opportunity cost negatively impacts the large-scale production of BOFs both in China and internationally. Therefore, there is need to develop alternative waste organic nitrogen sources to both replace defatted rapeseed meal in order to reduce BOF production costs and to identify an optimum secondary co-solid-fermentation process to ensure a maximum PGPF (Trichoderma spp.) population in BOFs. Currently, animal farms in China are growing a rapid pace with average mortality rates ranging between5% and 10%. Deceased animals are typically buried or are burned, resulting in air pollution and the waste of numerous biological resources. To address this, we have developed a method to produce amino acids by hydrolyzing dead animals inH2SO4 solution (3 mol/ L) at 100–105°C and 1.5–1.8 atmospheric pressure (China patent: ZL201410042218.3). The resulting amino acids are used as liquid fertilizer, as BOF additives, and have been used by several Chinese companies for the production of amino acid fertilizers. Immature BOFs have been shown to result in negative effects on both plant growth and soil properties [15]. Therefore, maturity assessme (...truncated)