Predictive correlations between reactions occurring in the gas, liquid, and solid phases are necessary to economically utilize the thermochemical conversion of agricultural wastes impacting the food, water, and energy nexus. On the basis of an: empirical mass balance (99.7%), this study established the Overall reaction stoichiometry (C33.42H45.95O20.26N0.22S0.14 = 0.50C(20.08)H(57.21)O(22.46)N(0.20)S(0.22) + 1.72H(2)O + 0.10H(2) + 1.07CH(4) + 0.02C(2)H(4) + 0.06C(2)H(6) + 2.21CO(2) + 2.05CO + 0.28C(63.75)H(32.47)O(3.23)N(0.43)S(0.12)) and energy balance for the slow pyrolysis of lignocellulosic pecan shell waste biomass at 10 degrees C min(-1) up to 500 degrees C. In situ thermogravimetry-gas chromatography and diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) were used to link the gas-, liquid-, and solid-phase nonisothermal reaction kinetics. Gaussian 'fit-based deconvolution of individual gaseous product formation rates (hydrogen, methane, carbon monoxide, carbon dioxide, ethylene, and ethane in mg min(-1)) suggested the relationships between (1) evolved methane and increased aromaticity/energy density of char product at 300-500 degrees C, and (2) evolved carbon dioxide and decarboxylation of char product near 400 degrees C. Partial least-squares (PLS) calibrations were obtained between (1) DRIFTS monitoring of the surface functional groups in the solid phase (transition from pecan shell to char) and (2) CO, CO2, CH4, C2H6, C2H4, and tar formation profiles in the gas/condensable phase. Established across-phase PLS calibrations can be used to predict biochar's surface chemistry based on the fingerprint of volatile products, and vice versa. These new thermodynamic (reaction stoichiometry and energy balance) and kinetic (deconvolution of specific gas formation rates and PLS) predictive methodologies will facilitate the nexus of food, water (designing of biochar soil amendment), and energy (optimization of syngas and bio-oil composition) enabling sustainable agriculture.