| Chemical fertilizer reduction and synergy becomes an important agricultural development direction at the present,because the fertility and productivity of soil could be decreased under chemical fertilizer with a single substance for a long term.Finding the organic fertilizer source substitute for some chemical fertilizer will be significant for agriculture.Moreover,the enormous mushroom residue(MR)could be good for crops and soils and potential chemical fertilizer succedaneum in the Chengdu Plain.However,it could has potential risks for soil and human under MR,which contains some heavy metals with few studies.Therefore,it is vital that researching the characteristics of material flow and energy flow and environmental risk assessment about farmland soil system under MR.There were seven treatments,including farmland soil system under no chemical fertilizer(CK),regular fertilizing(CF),25%N from MR(M1),50%N from MR(M2),75%N from MR(M3),100%N from MR(M4)and 125%N from MR(M5)with the balance of equal nitrogen from adding chemical fertilizer for field tests in 2 years.Then,the characteristics of material flow and energy flow of C,N,P,K,Cu,Cd,Pb and Zn were researched with the black box principle of farmland soil system and theories about mass balance and energy.And the environmental risks and optimal MR application rate were assessed in the Chengdu Plain in the study.Main conclusions of the study are as follows:(1)Characteristics of material flow in farmland soil system under MR applicationAfter applying MR to input C,N,P and K with Cu,Cd,Pb and Zn in farmland soil system,the functions and materials composition changed constantly in the soil system.The input materials from fertilization,seed,dry and wet deposition,irrigation water and crop residual were exported by pathways like crop,seepage and greenhouse gas emission and kept into soil system with different characteristics for each substance.?Carbon flow.There were 6 input ways which could import carbon into soil system,such as fertilization,seed,dry and wet deposition,irrigation water and residual crop.And the results showed the main carbon input way was fertilization and the total input quantity increased with increasing MR application rate under M1?M5 treatment in a rice-wheat rotation.Furthermore,there were 3 output ways which could export carbon out of soil system,such as crop,seepage and greenhouse gas emission.And the results showed the main carbon output way was greenhouse gas emission and its relative export amount decreased with increasing MR application rate,but the excess MR could took more absolute export amount of carbon substances under M1?M5 treatment in a rice-wheat rotation.Moreover,there were-865.94,479.83,1448.53,1918.95 and 2629.96 kg·hm-2 carbon substances imported into 0?40 cm soil,respectively occupied-30.61,11.82,27.77,30.22 and 35.19%of the total input(TTI),and increased with increasing MR application rate in a rice-wheat rotation.?Nitrogen flow.There were 6 input ways which could import nitrogen into soil system,such as fertilization,seed,dry and wet deposition,irrigation water and residual crop.And the results showed the main nitrogen input way was fertilization.Furthermore,there were 3 output ways which could export nitrogen out of soil system,such as crop,seepage and greenhouse gas emission.And the results showed the main nitrogen output way was crop and its export quantity increased firstly and then decreased with increasing MR application rate.Moreover,there were 175.39,153.35,156.89,188.19 and 288.01 kg hm-2 nitrogen substances kept into soil,respectively had 39.86,34.80,35.62,42.75 and 55.17%of TTI,and decreased firstly and then increased with increasing MR application rate in a rice-wheat rotation.?Phosphorus flow.There were 6 input ways which could import phosphorus into soil system,such as fertilization,seed,dry and wet deposition,irrigation water and residual crop.And the results showed the main phosphorus input way was fertilization and the total input quantity increased with increasing MR application rate under M1?M5 treatment in a rice-wheat rotation.Furthermore,there were 2 output ways which could export phosphorus out of soil system,such as crop and seepage.And the results showed the main phosphorus output way was crop and its relative export quantity decreased with increasing MR application rate under M1?M5 treatment in a rice-wheat rotation.Moreover,there were 138.07,253.80,406.05,562.82 and 722.41 kg·hm-2 phosphorus substances kept into 0?40 cm soil,respectively had 67.66,77.15,83.59,87.59 and 90.39%of TTI,and increased with increasing MR application rate in a rice-wheat rotation.?Potassium flow.There were 6 input ways which could import potassium into soil system,such as fertilization,seed,dry and wet deposition,irrigation water and residual crop.And the results showed the main potassium input way was fertilization and the total input quantity increased with increasing MR application rate under M1?M5 treatment in a rice-wheat rotation.Furthermore,there were 2 output ways which could export potassium out of soil system,such as crop and seepage.And the results showed the main potassium output way was crop and its relative export quantity decreased with increasing MR application rate under M1?M5 treatment in a rice-wheat rotation.Moreover,there were 41.48,69.08,179.83,304.03 and 436.39 kg·hm-2 potassium substances kept into 0?40 cm soil,respectively had 20.57,26.38,46.86,60.14 and 69.59%of TTI,and increased with increasing MR application rate in a rice-wheat rotation.?Copper flow.There were 6 input ways which could import copper into soil system,such as fertilization,seed,dry and wet deposition,irrigation water and residual crop.And the results showed the main copper input way was irrigation water and the total input quantity increased with increasing MR application rate under M1?M5 treatment in a rice-wheat rotation.Furthermore,there were 2 output ways which could export copper out of soil system,such as crop and seepage.And the results showed the main copper output way was seepage and its absolute export quantity increased with increasing MR application rate under M1?M5 treatment in a rice-wheat rotation.Moreover,there were 992.68,1149.35,1338.90,1516.50 and 1699.86 g hm-2 Cu residue in 0?40 cm soil,respectively had 29.00,31.65,34.81,37.34 and 39.76%of TTI,and increased with increasing MR application rate in a rice-wheat rotation.?Cadmium flow.There were 6 input ways which could import cadmium into soil system,such as fertilization,seed,dry and wet deposition,irrigation water and residual crop.And the results showed the main cadmium input way was dry deposition and the total input quantity decreased firstly and then increased with increasing MR application rate under M1M5 treatment in a rice-wheat rotation.Furthermore,there were 2 output ways which could export cadmium out of soil system,such as crop and seepage.And the results showed the main cadmium output way was seepage and its export quantity kept stable with increasing MR application rate under M1?M5 treatment in a rice-wheat rotation.Moreover,there were 23.23,23.17,24.60,26.31 and 28.26 g hm-2 cadmium residue in 0?40 cm soil,respectively had 56.63,55.63,56.83,58.51 and 60.53%of TTI,and decreased firstly and then increased with increasing MR application rate in a rice-wheat rotation.?Lead flow.There were 6 input ways which could import lead into soil system,such as fertilization,seed,dry and wet deposition,irrigation water and residual crop.And the results showed the main lead input way was dry deposition under M1?M4 treatment,the mail input way was fertilization under M5 treatment and the total input quantity increased with increasing MR application rate in a rice-wheat rotation.Furthermore,there were 2 output ways which could export lead out of soil system,such as crop and seepage.And the results showed the main lead output way was seepage and its absolute export quantity increased with increasing MR application rate under M1?M5 treatment in a rice-wheat rotation.Moreover,there were 1033.50,1162.71,1294.70,1420.86 and 1548.37 g·hm 2 lead residue in 0?40 cm soil,respectively had 83.97,84.42,84.36,83.97 and 83.70%of TTI,and increased with increasing MR application rate in a rice-wheat rotation.?Zinc flow.There were 6 input ways which could import zinc into soil system,such as fertilization,seed,dry and wet deposition,irrigation water and residual crop.And the results showed the main zinc input way was irrigation water and the total input quantity increased with increasing MR application rate under M1?M5 treatment in a rice-wheat rotation.Furthermore,there were 2 output ways which could export zinc out of soil system,such as crop and seepage.And the results showed the main zinc output way was seepage and its absolute export quantity increased with increasing MR application rate under M1?M5 treatment in a rice-wheat rotation.Moreover,there were 1664.18,1924.37,2234.05,2518.77 and 2925.38 g hm-2 zinc residue in soil,respectively had 30.43,32.87,35.73,37.90 and 41.57%of TTI,and increased with increasing MR application rate in a rice-wheat rotation.(2)Characteristics of energy flow in farmland soil system under MR applicationThrough importing renewable environmental resources,unrenewable industrial supplemental energy and renewable organic energy,the energy was changed in the farmland soil system with being exported by crop and seepage and stored some in soil.And there were some differences in characteristics,system diagram,productivity,rate of output and sustainable development index about energy under different treatments.?The total energy input under M1?M5 treatment respectively was 738.90×1014sej·hm-2,1034.70×1014 sej·hm-2,1476.22×1014 sej·hm-2,1917.57×1014 sej·hm-2 and 2383.74×1014 sej·hm-2 on the basis of solar emergy and increased with increasing MR application rates.And the renewable organic energy was the main input pathway kept 64.78,91.29,95.56,97.87 and 98.29%of the total energy input(TEI)under M1?M5 treatment.Excessive MR input showed no effect on crop productivity,because the energy exported by crop was 34.59,26.90,19.15,13.79 and 9.97%of TTEI and decreased with increasing MR application rate.Moreover,their stored energy was more 4.47,27.06,57.96,90.03 and 125.16×1014sej·hm-2 in soil under M1?M5 treatment than CF treatment,respectively had 4.52,5.41,5.88,6.20 and 6.46%of TTEI,and increased with increasing MR application rate.?The energy productivity under treatments from more to less were M3,M2,M4,M1,CF and M5.And the rate of net energy output were M1,M2(CF),M3,M4 and M5.Then the environmental loads rate under CF treatment was 17.01 about 39.70,340.20 and 850.50 times of M1?M3 treatment respectively.Moreover,the energy sustainable development index increased with Increasing MR application rate and it was between 1 and 10 only under M2 treatment.And it indicated that MR application could be good for productivity and environment stress and only soil system under M2 treatment could have more development potential and persistence than other treatments.(3)Environmental risk of farmland soil system under MR applicationThe excess MR application like M5 treatment made the biggest risk for soil and crops heavy metals,greenhouse gases and seepage among these treatments.On the contrary,the M2 treatment kept the lowest risk for soil heavy metals.And the M1 and M2 treatments kept the lower risk for crops heavy metals and seepage than other treatments(P>0.05).Moreover,the M2 and M3 treatments kept better for greenhouse gases than others(P>0.05).(4)Suitable application rate of MR in rice-wheat rotation in the Chengdu PlainThe suitable application rate of MR was 11763?12613 kg·hm 2·a-1 with assessment through economic benefit,heavy metal risk,greenhouse effect and seepage safety.And there would be 48684?52202 hm2 paddy field under this rate with estimating by available MR rate in the Chengdu Plain.Then it could decrease more than 8.59%chemical fertilizer application rate and reduce 3.01×107?3.32×107 kg(CO2-eq)greenhouse gases emission. |
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