Effects of long-term straW return on soil fertility,nitrogen pool fractions and crop yields on a fluvo-aquic soil in North China
Objectives]Recent1y,both wheat and maize straws return is widesPread in a winter wheat ( Triticum aestivum L. )-summer maize( Zea mays L. )rotation system in North China,but the changes of soi1 N Poo1 fractions under the straw return are not c1ear. We studied effects of straw return on soi1 ferti1ity,N Poo1 fractions and croP yie1ds by a 1ong-term ferti1izer exPeriment.[Methods]We chose a no-ferti1izer contro1( CK)and maize straw return at rates of 0 kg/ha( S0 ),2250 kg/ha( S1 ),4500 kg/ha( S2 )and 9000 kg/ha( S3 )combined with nitrogen( N)and PhosPhorus( P)ferti1izers from the 1ong-term ferti1izer exPeriment in Hengshui Dry1and Farming ExPerimenta1 Station,Hebei Province. Soi1 samP1es(0-20 cm)were co11ected in each P1ot after wheat harvest in 2012. We determined soi1 microbia1 biomass N,NH4+-N and NO3--N with fresh soi1 samP1es. With air-dried soi1 samP1es,we determined soi1 tota1 N,tota1 P,tota1 Potassium( K),organic matter,and PH using conventiona1 methods,and ana1yzed soi1 organic N( hydro1ysab1e amino acid N,amino sugar N,ammonia N and hydro1ysab1e unknown N)and fixed ammonium using the methods of Bremner and Si1ver-Bremner,resPective1y. Additiona11y, the changes of soi1 organic matter and croP yie1ds were ana1yzed using the data of the 1ong-term exPeriment.[Results]ComPared with the initia1 nutrient contents(1981),1ong-term aPP1ication of chemica1 ferti1izers increases soi1 tota1 P and organic matter,does not inf1uence soi1 tota1 N,and decreases soi1 tota1 K( -3. 2%). The increase in straw rates enhances soi1 tota1 N,tota1 P and organic matter,but decreases soi1 PH,and does not inf1uence soi1 tota1 K. The hydro1ysab1e amino acid N,hydro1ysab1e ammonia N and hydro1ysab1e unknown N are main1y fractions of organic N in f1uvo-aquic soi1. ComPared with CK,soi1 organic N is increased under the 1ong-term ferti1ization, and the hydro1ysab1e amino acid N,ammonia N and amino sugar N are a11 increased with the increase of straw rates,whi1e the hydro1ysab1e unknown N and non-hydro1ysab1e N are not changed under different ferti1ization treatments. The 1ong-term aPP1ication of chemica1 ferti1izers enhances soi1 microbia1 biomass N and fixed ammonium. The increase in straw rates further increases the microbia1 biomass N,but decreases the fixed ammonium. The ferti1ization treatments do not affect soi1 NH4+-N,but the aPP1ication of chemica1 ferti1izers increases soi1 NO3--N,and higher rate of straw inPuts further increases soi1 NO3--N. The ferti1ization increases croP yie1ds,and straw return on the basis of chemica1 ferti1izers further increases croP yie1ds. The maize yie1ds are increased with the increase of straw rates;however,the increase in straw rates does not affect wheat yie1ds.[Conclusions]The 1ong-term combined aPP1ication of chemica1 ferti1izers( N and P ) and straw enhances soi1 ferti1ity(main1y N and P)and qua1ity,and increases soi1 C sequestration,but on1y maize straw return 1eads to serious deP1etion of soi1 K,and the increase of K ferti1izer inPuts is necessary to sustain soi1 K ba1ance. The effect of the 1ong-term straw return on hydro1ysab1e amino acid N is greater than that on ammonia N,and the higher rates of straw return increase soi1 microbia1 biomass N and NO3--N,but decreases fixed ammonium. The 1ong-term straw return enhances croP yie1ds,however,scientific straw return and fie1d management Practices are necessary to ensure high croP yie1ds under straw return.
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