Effect Of Fertilizer Nitrogen Management On Transformation And Availiablity Of Straw Nitrogen

The purpose of this paper is to study the transformation and bioavailability of nitrogen?N? from crop straw for providing scientific information and guidelines on effective straw returning and N management. Pot experiments and field experiments were conducted using 15 N isotope techniques to study the effect of N fertilizer management and microbial inoculants of straw decomposition on N transformation and bioavailability of straw N, contributions of straw N and fertilizer N to plant uptake N as well as availability of residual fertilizer N and straw N under different N managements, and the effect of straw returning or no straw returning on the yield of winter wheat and summer corn as well as soil fertility under different fertilization models. The following results were obtained:1. Pot experiments were conducted by one season winter wheat and two following season corn to study the effect of N rate, combination of chemical fertilizer N with manure N and addition of microbial inoculants of straw decomposition on N transformation and bioavailability of N from 15 N labeled corn straw(¹⁵N-straw). Resulted indicated that:1) Recovery of ¹⁵N?REN? from ¹⁵N-straw by winter wheat was 7.14% to 10.32%, while the residual REN from ¹⁵N-straw by the 1st and 2ed following corn was 3.75% to 5.51% and 2.28% to 3.18%, respectively. Total of 13.13% to 18.60% of ¹⁵N-straw N was recovered, 55.63% to 69.16% remained in soil and 17.26% to 26.09% lost after three cropping. N application increased REN compared with control without N application. N fertilizer rate and manure substitution for fertilizer N did not influence REN from ¹⁵N-straw by winter wheat and the 2ed corn, but reducing fertilizer N decreased REN by the 1st corn and three crops, but increased when applied with manure. Addition of microbial inoculants significantly improved straw REN by winter wheat and the 1st season corn and total of three cropping and reduced residual and loss of N from ¹⁵N-straw.2) In wheat plant percent of N derived from ¹⁵N-straw?%Ndfs? was 6.30% to 14.25%, reduced by N application compared with control without N fertilizer application. Combination of fertilizer N and manure resulted in higher wheat %Ndfs than fertilizer N alone. Addition of microbial inoculants did not influence wheat %Ndfs compared with treatments without microbial inoculants. The plant %Ndfs by the following 1st and 2ed corn was, respectively, 1.13% to 3.73% and 1.67% to 5.97%, reduced by N application but no difference between N treatments. Addition of microbial inoculants reduced corn plant %Ndfs from residual ¹⁵N-straw.3) The %Ndfs of soil mineral N?Min-N? after wheat was 0.51% to 2.80%, decreasing with increasing rate of N fertilizer. The %Ndfs of soil microbial biomass N?MBN? was 2.43% to 2.54%, no difference between N treatments. The %Ndfs of soil Min-N after 1st and 2ed corn was 0.66% to 0.78% and 0.45% to 1.16%, while the MBN %Ndfs was 1.97% to 2.18% and 1.32% to 1.73%, no difference among N treatments. Addition of microbial inoculants increased %Ndfs of soil Min-N while decreased %Ndfs of soil MBN after wheat and 1st corn, but no effect after 2ed corn.2. Pot experiments were conducted by one season winter wheat and one following season corn to study transformation of 15 N labeled urea(¹⁵N-urea) N and ¹⁵N-straw N and their contribution to crop uptake N as affect by fertilizer N ratio of basal to topdressing and combination of fertilizer N with manure N. Results indicated that:1) The REN and the residual of ¹⁵N-straw was 16.15% to 18.08% and 32.94% to 54.00%,while the REN of ¹⁵N-urea was 32.61% to 39.55% and 16.78% to 40.03%. The higher the ratio of basal to topdressing of N fertilizer, the higher the REN of ¹⁵N-straw, the lower the REN of ¹⁵N-urea. Combination of chemical fertilizer N with manure N did not affect REN of ¹⁵N-straw while decreased REN of ¹⁵N-urea compared with fertilizer N alone.2) Wheat plant %Ndfs in regreening stage, heading stage and maturity stage was 9.55% to 10.58%, 8.30% to 10.15% and 8.28% to 9.92%, Plant uptake N derived from ¹⁵N-urea?%Ndfu? in three stages was 18.62% to 34.97%, 26.67% to 39.56% and 23.77% to 35.86%, respectively. The higher ratio of basal to topdressing of N fertilizer, the higher plant %Ndfs, the lower plant %Ndfu. Combination of chemical fertilizer N with manure N increased plant %Ndfs, decreased %Ndfu compared with fertilizer N alone.3) Soil min-N %Ndfs at regreening stage, heading stage and maturity stage was 0.73% to 4.76%, 0.34% to 1.98% and 0.60% to 0.84%, min-N %Ndfu was 1.48% to 4.16%, 1.38% to 2.33% and 0.97% to 1.84%, respectively. Soil MBN %Ndfs at three stage was 6.58% to 13.24%, 3.12% to 3.68% and 3.72% to 4.26%,while MBN %Ndfu was 8.11% to 32.89%, 5.73% to 17.05% and 4.64% to 7.04%, respectively. Combination of chemical fertilizer N with manure N increased %Ndfs and decreased %Ndfu of soil min-N compared with fertilizer N alone at regreening stage and heading stage. Soil MBN %ndfs decreased with increase ratio of basal to topdressing only at regreening stage, while soil MBN %ndfu increased with increase ratio of basal to topdressing at regreening and heading stage, but decreased at maturity.4) The REN of 15 N from residual ¹⁵N-straw and ¹⁵N-urea by the following summer corn was 3.09% to 4.68% and 2.46% to 3.53%. The %Ndfs and %Ndfu of uptake N by corn was 2.71% to 3.39% and 3.58% to 4.14%. The residual rate of ¹⁵N-straw and ¹⁵N-urea after corn was 29.74% to 31.84% and 18.49% to 20.87%, respectively. Application of fertilizer N with manure increased availability of residue ¹⁵N-straw compared with fertilizer N alone, while basal application of all fertilizer N increased availability of N both from residual ¹⁵N-straw and ¹⁵N-urea.3. Field experiments were conducted under rotation of winter wheat and summer corn to study the effect of different fertilization models on crop yield, N uptake and soil fertility on the condition of straw returning or no straw returning. Results indicated that:1) Compared to application of only chemical N with no straw returning, mixed application of organic N and chemical N combined with straw returning significantly increased the grain and straw yield of summer corn as well as N uptake of winter wheat and summer corn at maturity stage on condition of recommended N rate2) Compared to no straw returning, straw returning significantly increased soil organic matter, NO3--N, MBN and availiable potassium content meanwhile it promoted the activity of soil enzymes including ?-glucosidase, cellobiohydrolase, ?-xylosidase and N-acetyl-glucosaminidase.