Study On Selection And Mechanism Of Nitrogenconservation Additives Duning Swine Manure-straw Composts

Nitrogen loss is a ubiquitous phenomenon during composting, and the method ofcontrolling nitrogen loss is a key question for compost study, so the nitrogen transformationprocess is the base of controlling nitrogen loss during composting. Pig manure and wheatstraw were taken as raw materials, the objective of the study were: i) the C and N dynamicsduring the composting in a self-built, static forced-air composting box (90L); ii)The effect ofthe pig manure and straw composting with different dosages of grape seed; iii)The effect ofcompost with apple pomace, bentonite and calcium superphosphate in the compost. It ordersto investigate the effect of additives on nitrogen conservation during composting and itseffects on material changes of the composting process. It will provide theoretical basis andreference data for nitrogen losses control in the manure composting. The main conclusionswere as follows:(1) Fresh swine manure and wheat straw were mixed at a7:1ratio and then composted ina self-built composting box. The NH4+-N concentration in the compost had declined by74.1%,the total N concentration had declined by14.4%. In contrast, the NO3-N concentrationincreased by103%. On a mass basis,40.2%of original amount of N was lost duringcomposting,49%of that N was lost during the first4d of composting. Humic acidconcentration increased by2.4%during composting. After23d, the seed germination index(GI) was87.1%, the NH4-N-to-total N ratio was5.1, and the humification ratio (HR) wasstable, indicating that the compost had stabilized. It was suggested that proper ventilation andpile-turning at the stable stage could reduce the loss of nutrients from the compost.(2) Pig manure and straw were mixed at a ratio of10.5:1and added8%and15%grapeseed respectively, then compost. The results showed that: grape seeds can prolong the hightemperature period and reduce the fluctuations of temperature. The high-temperature periodwas16d and10d under the grape seed adding ratio of8%and15%. After30d, the NO3-Nconcentration increased by18.3%,33.1%and30.1%in control,8%and15%treatment; and inthose treatments, total nitrogen increased by24.8%,16.5%and16.1%respectively; the reducerates of organic carbon were22.8%,19.7%and22.2%; the nitrogen loss rates were35.6%,34.7%and35.1%, so the treatments of grape seeds were lower than that of the control. All treatments stabilized after30d. Adding grape seeds was in favor of nitrogen and carbonconservation, to be more exact, the effect of8%adding treatment was better than that of15%.(3) Pig manure and straw were mixed at a ratio of10.5:1and added apple dregs,bentonite and calcium superphosphate respectively. They all prolong high temperature period,compared with the control, and4,9,4d extensions respectively. The treatments of calciumsuperphosphate reduced the ammonia volatilization in composting process and increased thetotal nitrogen concentration, but bentonite increased the ammonia volatilization and reducedthe total nitrogen concentration. All of them can reduce the nitrogen loss, and the nitrogenloss of superphosphate was22.5%lower than the control, then followed by Apple pomace andbentonite.(4) In the self-built, static forced-air composting box, the more appropriate mixingthe ratio is7:1for pig and straw and the C/N was17. Among the different additives, calciumthe effect of superphosphate was best, while bentonite was the worst. Temperature and pH hada significant negative correlation with humus, which need to be do controlled reasonably inthe composting. It was beneficial to the form of humus by adding of some carbon-richmaterial.