Objectives Polyaspatric acid (PASP) is added during aerobic composting to decrease the nitrogen loss. The effect and mechanism of the nitrogen retention by PASP were studied in this paper.
Methods The dehydrated cow dung was used as composting material. First, the PASP was added in rate of 0 g/t (CK), 120 g/t (A) and 240 g/t (B) during composting experiment. The physicochemical indexes, N content and maturity of the compost were measured periodically since the beginning of the composting. Then, according to the loading amount of PASP in biochar by special process, the PASP loaded biochar (BP) and the blank biochar (BC) were adding into dehydrated cow dung with the same dosage (80 g/kg) separately, and sealed in mesh bags for fermenting in the composting stack. The morphology were scanned by electron microscopy (SEM), the change of functional groups was measured using fourier transform infrared spectrometer (FTIR), and the nitrogen binding forms of PASP and humification degree were observed using X-ray photoelectron spectroscopy (XPS).
Results At the beginning of composting, comparing with BC, the morphology of granulation existed in the surface of BP. The specific morphology was intensified by composting during high temperature period. The pH value of PASP added group was higher than that of CK, all indicated that PASP was only partially decomposed during composting. According to the variations of physicochemical indexes, N content and microstructure characteristic, the content of ammonium N was increased during the high temperature period, especially from the fifth to the tenth day. It was tend to attribute the phenomenon to the chelating of ammonium N by the carboxyl from the side chain of PASP. Meanwhile, the phenomenon caused difficult use of ammonium by microbial. Then, the humification period arrived 4.0–4.6 days earlier while the accumulated temperature during high temperature period was reduced by 40.0℃–91.9℃, compared with the CK treatment. Eventually, the risk of N loss during high temperature was reduced. The analysis results about the FTIR of DOM in compost pile showed that the relative degree of aromatization could be strengthen by the addition of PASP, and the supply ability of available nitrogen during humification period could be promoted by the function of nitrogen retention of PASP in the high temperature period, which led to the decline of mineralization intensity. Thus, the risk of nitrogen loss during humification period was reduced by the combination of nitrogenous compounds and aromatic compound. Finally, the total amount of ammonia volatilization had been lowered by 26.62%–37.02% compared with CK treatment (P < 0.05), and the total N amount of the PASP treatment had been increased by 7.09%–13.64% at the 39th day compared with the beginning of compost, while CK treatment had been lowered by 1.23% (P > 0.05).
Conclusions The PASP could retain ammonium ions through the direct complexation between carboxyl and ammonium. At the same time, addition of PASP could decrease the cumulative temperature during the high temperature period, and shorten 4.0–4.6 days of the post humification period, which is the most important mechanism for reducing nitrogen loss by PASP. The most economic dosage for the dehydrated cow manure compost is adding PASP 120 g/t.
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