For the dual purposes of the straw resource utilization and strengthening the biomass carbon basal application

the rushes straw in the Dongting Lake was pyrolysised as biomass substrate. Using the coated and mix granulation technologies

the coated (CT) and mixed (MT) biochar fertilizers were prepared

with modified starch as adhesive

and bentonite

humic acid as supplementary. The ratios of biochar in fertilizers were 10% (T1)

15% (T2)

20% (T3)

25% (T4) and 30% (T5) respectively. All the fertilizers were screened considering the microstructure

nutrient release rate

particle size and compressive strength and other basic properties. A pot experiment was carried out with the screened biochar fertilizers (CT2

CT3

CT4 and MT1

MT2 and MT3)

taking common compound fertilizer (NPK) and no fertilizer as the control (CK). The differences of ammonia volatilization and nitrogen leaching and loss in paddy soil were analyzed. The results showed that the larger ratio of biochar resulted in the compacted fertilizer structure and the lower cumulative nitrogen release rate. However

the excessive addition of biochar would cause the uneven particle size and non-standard compressive strength of fertilizer. For CT

15%~25% biochar was suitable. For MT

10%~20% biochar was suitable. Compared with NPK

CT2

CT3 and CT4 reduced ammonia volatilization accumulation by 12.95%

27.96% and 23.82%

and ammonia volatilization loss rate by 16.56%

35.67% and 30.57%

respectively

among which CT3 had the best effect. The cumulative amount of ammonia volatilization was reduced by 33.72%

41.48% and 16.06% respectively in MT1

MT2 and MT3

and the loss of ammonia volatilization was reduced by 43.31%

53.18% and 20.38% respectively. The average concentration of ammonium and nitrogen in surface water decreased by 20.74% (CT4) and 39.90% (MT2)

respectively

compared with NPK. Total nitrogen and nitrate nitrogen concentration of MT decreased by 5.50% and 5.09% respectively in MT2

while the difference of CT was not significant. Compared with NPK

CT significantly reduced the average concentration of ammonium nitrogen and total nitrogen by 8.93%~14.00% and 8.84%~16.38%

respectively

while there was no significant difference in nitrate nitrogen treatments. The average concentrations of ammonium nitrogen

nitrate nitrogen and total nitrogen were reduced by 11.16%~12.42%

3.22%~22.29% and 11.14%~15.86%

respectively. The higher the ratio of biochar was

the more obvious the emission reduction of biochar was. But the effect was not obvious when the excessive biochar was added. In general

the two methods could effectively reduce the loss of ammonia volatilization and reduce the loss risk of nitrogen. Among them

the CT with 20%~25% biochar content was the best

and the MT with 15% was the best.