| Red soil phosphorus fixation is intense,crop utilization efficiency is low,flue-cured tobacco production in a large number of inorganic fertilizer inputs exacerbated the phosphorus fixation or ineffective.Organic fertilizers applied alone or in combination with inorganic fertilizers can effectively enhance soil phosphorus effectiveness,and different application methods have different effects on soil phosphorus forms and their effectiveness.In this paper,a field plot trial of organic fertilizer stratified application was conducted in a typical red soil baked tobacco growing area in Panzhihua,with four treatments: T1(conventional fertilizer application),T2(organic fertilizer 100% shallow application),T3(organic fertilizer 100% deep application),T4(organic fertilizer 50% shallow application + 50% deep application).To investigate the growth conditions of flue-cured tobacco,soil physicochemical properties,soil phosphorus fraction and the response of microorganisms encoding phosphatase genes(phoD)to different application methods of organic fertilizers,and to provide a reference for fertilization methods to enhance soil phosphorus effectiveness.The main research results are as follows:(1)Organic fertilizer application increased the leaf length,leaf width and leaf number of flue-cured tobacco,and significantly improved the dry matter accumulation of flue-cured tobacco,and the effect of stratified application of organic fertilizer was more obvious.Compared to T1,organic fertilizer application increased leaf length,leaf width and leaf number at maturity of flue-cured tobacco by 10.75%-18.59%,36.99-44.74% and 0.99%-15.95%,respectively,with T4 treatment increasing leaf width significantly by 5.64%-5.67% compared to T2 and T3.Compared with the T1 treatment,organic fertilizer application increased the above-ground dry matter accumulation of flue-cured tobacco throughout the reproductive period,especially at maturity by 94.59%-164.18%.Meanwhile,organic fertilizer application promoted root dry matter accumulation in the fertilized areas during the maturity of flue-cured tobacco,where T2 significantly increased root dry matter mass in the 5-10 cm soil layer by 17%-21.53% compared to T1 and T3,and T3 significantly increased root dry matter accumulation in the 20-25 cm soil layer by 100.35%-186.64% compared to T1 and T2,and T4 dry matter quality was enhanced by37.40%-66.98% and 2.60%-214.89% in these two soil layers compared to T2 and T3,respectively.(2)Organic fertilizer application can maintain soil pH stability and significantly increase soil organic matter and available phosphorus content.The T4 treatment with a double layer of organic fertilizer maintained stable soil pH between the vigorous growing and mature stages of flue-cured tobacco,with a variation of 0.12-0.16 units.Organic fertilizer application increased the soil organic matter content in the fertilized area at mature stage of flue-cured tobacco,where T2 significantly increased 0.93-1.23 g/kg in 5-10 cm soil layer compared with T1 and T3,and T3 significantly increased 1.26-2.15 g/kg in 20-25 cm soil layer compared with T1 and T2,while there was no significant difference with T4.T4 significantly increased the effective phosphorus content in the 5-10 cm soil layer during the vigorous growing stage compared with T1 and T3 treatments by 32.66%-54.49%,which was not significantly different from T2,and significantly increased in the 25-30 cm soil layer during the vigorous growing stage compared with T1 and T2 by 96.78%-99.57%,which was not significantly different from T3.This indicates that 50%shallow + 50% deep application of organic fertilizer can significantly enhance the phosphorus effectiveness of the whole soil layer and is as effective as the full application of organic fertilizer in a single layer.Organic fertilizer application increased soil Al-P and active organophosphorus content and significantly decreased soil O-P and highly stable organophosphorus content.The Al-P content in the 10-15 cm soil layer of T2 treatment and 20-25 cm soil layer of T3 treatment were elevated by33.72% and 50.92%,respectively,compared with the corresponding soil layers of T1 treatment during the rosette stage.Meanwhile,the active organic phosphorus content in the 5-10 cm soil layer of T4 treatment increased 29.39%-36.69% compared with T1 and T3 treatments,and11.55%-72.75% in the 20-25 cm soil layer compared with T1 and T2 treatments during the baking tobacco rosette stage.Compared with the other treatments,the O-P content of the 10-15 cm soil layer in the T4 treatment was reduced by 1.15-7.89 mg/kg and 0.74-15.59 mg/kg during the vigorous growing stage and mature stage,respectively,and the highly stable organic phosphorus content of the 10-15 cm soil layer was reduced by 7.7-11.39 mg/kg during the mature stage.This indicates that the treatment of 50% shallow + 50% deep application of organic fertilizer can enhance the content of active phosphorus fraction in the whole soil layer,reduce the content of difficult-to-use phosphorus in the middle and lower layers,and coordinate the phosphorus supply of the soil.(4)Organic fertilizer application increased acid phosphatase activity in the soil,and two-layer application of organic fertilizer increased phoD gene microbial community diversity.Compared to T1,acid phosphatase activity at mature stage was increased by 40.72% in 5-10 cm soil layer in T2 and 29.98% in 20-25 cm in T3.T4 increased acid phosphatase activity by16.78%-29.43% in the 5-10 cm soil layer compared to T1 and T3,and by 8.95%-23.7% in the20-25 cm soil layer compared to T1 and T2.For the phylum level phoD gene microorganisms,the relative abundance of the phylum Proteobacteria in the 10-15 cm soil layer was higher in T2 than in the other treatments,and the relative abundance in the 20-25 cm and 25-30 cm soil layers was higher in the T3 and T4 treatments than in the T1 and T2 treatments.While at the genus level,the Bradyrhizobium was the absolute dominant genus,and the T4 treatment had the highest relative abundance in the 5-10 cm and 15-30 cm soil layers.Meanwhile,the Alpha diversity index showed that T4 had a higher Chao1 index than the rest of the treatments in the5-10 cm and 10-15 cm soil layers,and the highest Shannon index in the 5-10 cm and 25-30 cm soil layers.In conclusion,the application of organic fertilizer increased soil nutrient content,changed phosphorus forms,enhanced phoD microbial community diversity,and significantly improved soil phosphorus effectiveness.Single-layer application of organic fertilizer can only enhance the effectiveness of phosphorus in the fertilized area,while double-layer application of organic fertilizer takes into account both shallow and deep soils,which can not only meet the phosphorus needs of flue-cured tobacco in shallow soils,but also solve the problems of insufficient supply of phosphorus in the deep layer of flue-cured tobacco and the difficulty of rooting down.Therefore,a fertilization method of 50% shallow + 50% deep application of organic fertilizer(4500 kg/hm2)is recommended in flue-cured tobacco production. |
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