Calculation methods of total nitrogen and total phosphorus distribution in pig manure fractions

Introduction. The study aims to develop and test a comprehensive calculation methodology in a case study of pilot pig complexes to verify reliability of estimates. The methods are required for reliable tracking of the nutrients flow at the farm level and for adjusting the application doses of resulting solid and liquid organic fertilizers with due account for the crop rotation in place, agrochemical analysis of soils, and specific crops to obtain the target yields. Materials and Methods. Calculations of the content of total nitrogen and total phosphorus in pig manure before separation and in resulting solid and liquid fractions were carried out by the developed method. At that, coefficients from corresponding normative documents and results of previous research were used. Samples of initial material were collected in three replications at two closed-cycle pig rearing complexes located in the Leningrad Region. The experimental data were statistically processed with StatGraphics Centurion v.16 software. Results. The calculated nutrient content of the manure before separation and the separated solid and liquid fractions was compared with the results of laboratory analysis of the physicochemical composition of the manure and its fractions from the selected pig rearing complexes. The difference between the calculated and average actual values of all considered indicators did not exceed 10%, with the differences in nitrogen content turning out to be much bigger (up to 10%) than the differences in phosphorus content (up to 5.7%) in the solid and liquid fractions of pig manure. Discussion and Conclusion. The identified differences can be explained by the instrumental uncertainty and heterogeneity of the analyzed initial material - a mixture of excrement and process water. The results of the study confirmed that the developed method is reliable, and it can be used to account for the nutrients in the solid and liquid organic fertilizers in calculating and adjusting doses for certain crops to produce expected yield and reduce the negative impact on the environment.