Effects Of Successive Straw Biochar Application On Crop Growth, Soil Fertilizty And Ammonia Volatilization In Three Agricultural Soils With Varying Properties And Crop Rotations

Biochar refers to artificially produced high carbon solid materials through thermaldegradation of biomass under an oxygen-limited environment and in the general temperaturerange250oC~700oC.We investigated rice/wheat crop growth, nutrient uptake by crop plants as well as soilphysicochemical characteristics after the successive incorporation of biochar from rice strawinto a rice-wheat rotated soil during a2-year (four rice/wheat rotation seasons) pot experiment,with the aim of evaluation the effects of crop straw biochar on soil productivity and Csequestration in paddy soil of the Tai Lake plain. The biochar application rates was0(ascontrol; CK),4.5t/ha and9.0t/ha. Each treatment had triplicate pots. Each pot was kept thesame dosage of NPK fertilizer, the same application methods as well as the similar watermanagement. Before each crop season, the biochar (passed through a2-cm sieve)homogeneously mixed with0~10cm soil in pots. The results showed that soil total organiccarbon and soil total nitrogen increased with increasing biochar application. Total soil organiccarbon and TN increased by46.7%~113%and9.28%~28.3%at9.0t/ha biochar appicationrate in the four crop seasons, respectively. No difference in dissolved organic carbon(DOC)was recorded between biochar-treated and control soils. Biochar application increased theabove-ground biomass of rice/wheat (grain yield increased by11.4%~60.5%, straw yieldincreased by15.0%~56.8%) as well as enhanced the accumulation of N、P、K、Mg and Ca.Accordingly, soil total nitrogen as well as soil available nutrients (Mehlich III extraction) suchas available P, K, Mg and Ca was increased after biochar application. In addition, biocharamendment also enhanced soil pH, cation exchangeable cations (CEC) but decreased soil bulkdensity. Both the biochar application at the rates of4.5t/ha and9.0t/ha have significantlyimproved soil pH and CEC during the two rice/wheat rotation cycles, which could have reachup to6.79and12.7cmol/kg especially at the application rate of9.0t/ha biochar, respectively.After2011rice season, bulk density of the soil have greatly decreased by8.03%and12.2%incomparsion with the control at the rates of4.5t/ha and9.0t/ha biochar application. Nodifference in DOC was recorded between biochar-treated and control soils. Those resultsdemonstrated that the successive application of biochar produced from crop straw could sequester C and increase C storage capacity as well as ameliorate soil properties, improve soilfertility and enhance crop productivity in rice/wheat paddy soil of the Taihu Lake region.However, whether it can be a sustainable technology to improve soil fertility and sequestrateC for a long term still needs to be validated in the field conditions.A pot experiment over an entire wheat/millet rotation was conducted to examine the effectof rice straw biochar on crop growth, soil physiochemical and nutrient properties in a uplandCambosols (pH8.25) and a upland Oxisols (pH4.80) from northern and southern Chinauplands.Biochar was incorporated into0~10cm top soils at rates of0,2.25t/ha and22.5t/haat the initial of each crop season with an identical dose of NPK fertilizers. Crop biomassshowed an increase trend with increasing biochar application rate over a wheat/milletrotation.In the oxisols, the22.5t/ha biochar treatment enhanced soil pH and cation exchangecapacity, decreased soil bulk density, improved soil P, K, Ca and Mg availability andenhanced their uptake, and increased wheat and millet yields by157%and150%for wheatgrain and straw, respectively, and72.6%for millet straw. In the cambosols, biochar treatmentdecreased soil bulk density, improved P and K availability, increased N, P and K uptake bycrops and increased wheat and millet straw yields by19.6%and60.6%, respectively. TOCincreased in response to successive biochar applications ove the rotation. No difference inDOC was recorded between biochar-treated and control soils. Our results hint that theimprovement effect of biochar application on Oxisols is superior to that on Cambosols.Converting straw to biochar and treating soils with successive applications may be a viableoption for improving soil quality, sequestering carbon and utilizing straw resources in China.In the above-mentioned three pot experiments, we measured ammonia (NH3)volatilization during each crop growing seasons after urea applications using a continuous airflow enclosure method. In the paddy soil, biochar treatments had little effects on NH3volatilization at first rice/wheat rotation; however, in the second rotation,9.0t/ha biochartreatment suppressed NH3volatilization in the rice season while stimulated it in the wheatseason. In the acidic Oxisols (pH4.80), NH3volatilization was enhanced by22.5t/ha biochartreatment in both wheat and millet growing seasons. In the alkinline Cambosols (pH8.25),22.5t/ha biochar treatment increased NH3volatilization in the first wheat season; nevertheless,this increasing effect was not found in the following millet season. Our results showed thatbiochar treatments had substantial influences on NH3volatilization. However, the positive ornegative influences of biochar on NH3volatilization varied greatly with soil types, croprotations and biochar application rate. Nevertheless, the effect of biochar application on Ncycling through NH3volatilization needs to be further assessed before full-scale successiveapplications to agricultural fields are implemented.