Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Plant and Environmental Science

Committee Chair/Advisor

Nishanth Tharayil

Committee Member

Christopher Kitchens

Committee Member

Christopher Ray

Committee Member

Patrick Gerard


The current fertilizer regime heavily relies on inorganic fertilizers to meet the crop nitrogen (N) and phosphorus (P) demand. However, the United States has a limited N production capacity, with 50% N demand met through imports. On the other hand, the nonrenewable natural reserves of P are being depleted at an unprecedented rate and are expected to be exhausted with in next 100 years. Additionally, high solubility/liability of the field applied inorganic fertilizers often results in lower nutrient use efficiency (NUE; <40% for N and <25% for P) due to environmental losses/fixation, which further aggravates the stress on already stretched non-renewable nutrient resources to meet crop demand. Therefore, it is highly advantageous to explore the potential of alternative slow-release N and P sources that can improve the NUE and supplement the current fertilizer regime. Rendered animal materials, such as meat and bone meal (MBM), are one of the promising candidates for supplementing the inorganic fertilizers, due to their high nutrient content (e.g., 8% N; 5-10% P and 10-20% Ca), and availability (2.5 million tons in the US; 18 million tons EU). However, rapid N and slow P mineralization from MBM, that is less synchronized with crop demand could lead to significant nutrient losses/soil buildup of N and P, respectively. This necessitates measures to modify the mineralization rates for their efficient, economical, and sustainable utilization as supplement fertilizer. To address these challenges, in this study, different natural (neem and karanja) and microbial (arbuscular mycorrhizae and phosphorus solubilizing fungi) amendments were utilized to regulate the N and P mineralization rates from MBM. The effect of MBM formulations on soil microbiological health, produce quality, and their potential to supplement the highly soluble inorganic N fertilizers was evaluated under field conditions.

The MBM led to rapid N mineralization, with 35% of the applied N mineralized within the first five days of incubation. Pelletization of non-extracted MBM (size: 4 × 3 mm) decreased the N mineralization (ammonification) rate by 30% compared to non-pelletized MBM. Neem and karanja (natural nitrification inhibitors: NIs) reduced the nitrification rate of MBM by ~40% and increased the retention of NH4+ (~35%) in the soil as compared to MBM alone. The MBM exhibits a slow P mineralization rate (>75% of the total P as calcium bound P), with only 8% of the P in MBM was net mineralized within the first 36 days after incubation. The simultaneous application of both arbuscular mycorrhizal fungi and P. bilaiae in association with MBM resulted in 2-fold higher P mobilization and P uptake by maize as compared to MBM alone. In addition, P. bilaiae with MBM decreased the calcium bound P content in the soil by 26% than MBM alone. Apart from improving soil nutrient status, application of MBM increased the soil CO2 respiration (7-fold), soil potential enzymatic activity (protease: 4-fold; acid and alkaline phosphomonoesterases: 2-fold), and microbial abundance (gram-positive bacteria- 2.5-fold; gram-negative bacteria- 2.5-fold; fungi- 2-fold) as compared to control. The NIs did not negatively affect the microbial growth and functionality except for lower biomass in gram-negative bacteria in MBM + NIs as compared to MBM alone. Arbuscular mycorrhizal fungi inoculation with MBM also increased the plant photosynthesis rate (27%) and root phosphomonoesterase activity (40%), then MBM control.

The standardized MBM formulations were tested in field experiments, as a supplement to inorganic N fertilizer for their effects on crop growth and N recovery. The application of non-extracted MBM (NEMBM) in three splits (25% N through NEMBM) N scheduling resulted in higher grain yield and NUE than that of CaNO3 (100%) in two splits N scheduling, extracted MBM (EMBM) in 3 splits (25% N through EMBM) N scheduling, and control. A similar grain yield of maize was observed between the integrated application of NEMBM (37.5% N through NEMBM) and CaNO3 in 2 split N scheduling and recommended CaNO3 (100%) in 3 split N scheduling. The integrated application of NEMBM (25-37.5% N) resulted in lower NO3- (4-9%) leaching than CaNO3 (100 % N) in 3 and 2 splits N scheduling. The integrated application of EMBM and CaNO3 in 3 splits N scheduling resulted in higher NO3- leaching than the integrated application of NEMBM and CaNO3 in 3 splits scheduling.

We further investigated the effect of different mineral N forms (CaNO3: NO3-, NH4SO4: NH4+, and organic N: meat and bone meal-MBM) on the aroma (volatile profile), primary, and secondary metabolite profile in the fruits of Fragaria vesca (cv. French alpine) using an untargeted metabolomics approach. Fertilization with MBM resulted in higher aroma-related volatile compounds (esters: 2-5 fold, alcohols: 3-6 fold, and fatty acids: 1.5-3 fold) and tricarboxylic acid (TCA) cycle organic acids (20-57.4%) in the strawberry fruits than CaNO3. Whereas higher sugars, sugar alcohols (21.6%), and amino acids (24.5%) content were observed in the CaNO3 than NH4SO4 and MBM. The MBM significantly increased the cellular content of flavonoids (including anthocyanins: 20.8-40.5%), and hydrolyzable tannins (6.4-28.9%; galloyl glucoside, and ellagic acid derivatives) than CaNO3.

Collectively, our studies demonstrate that MBM blended with NIs, arbuscular mycorrhizae fungi, and P. bilaiae could increase the crop NUE via lowering N losses, improving P mobilization and uptake efficiency from MBM and soil microbiological health. Further, NEMBM can be efficiently used to supplement inorganic N fertilizers to maintain the equivalent grain yield and NUE of maize while reducing the number of N fertilizer split applications and soil N leaching losses. The precise application and management of MBM can be employed to enhance the phytonutrient content (organic acids, flavonoids, and hydrolyzable tannins) and aroma (volatile profile) in the strawberry fruits. Moreover, such a strategy can recycle up to 1.08 million tons and 2 million tons of rendered animal materials in the United States and Europe, respectively, for plant nutrition each year.

Available for download on Thursday, November 17, 2022