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Effects of cropping system and fertilization regime on soil phosphorous are mediated by rhizosphere-microbial processes in a semi-arid agroecosystem.
Journal of Environmental Management ( IF 8.7 ) Pub Date : 2020-07-08 , DOI: 10.1016/j.jenvman.2020.111033
Mahnaz Roohi 1 , Muhammad Saleem Arif 1 , Tahira Yasmeen 1 , Muhammad Riaz 1 , Muhammad Rizwan 1 , Sher Muhammad Shahzad 2 , Shafaqat Ali 1 , Luca Bragazza 3
Affiliation  

In semi-arid regions, soil phosphorus (P) dynamics in cereal-legume intercropping are not yet fully elucidated, particularly in relation to integrated application of fertilizers. To this aim, we investigate the effects of different fertilizers on various P fractions in relation to the rhizosphere-microbial processes in a cowpea/maize intercropping system. Field experiments were conducted during two consecutive years (2016–2017) in a split-plot design by establishing cowpea/maize alone or intercropped onto the main plot, while the sub-plot was treated with four types of fertilization, i.e. no fertilizer addition (control), organic amendment (compost), mineral fertilizers (NPK) and multi-nutrient enriched compost (NPKEC). Our results showed that NPKEC fertilizer increased NaHCO3-Pi by 69% in maize, 62% in cowpea and 93% in intercropped plots compared to control plots. Similarly, a significant increase in the NaHCO3-Po fraction was also recorded with NPKEC treatment in all cropping systems. In case of moderately labile P, NPKEC fertilizer caused the highest increase of NaOH-Po (12.87 ± 0.50 mg P kg−1 soil) and NaOH-Pi (22.29 ± 0.83 mg P kg−1 soil) fractions in intercropped plots. Except for intercropping, NPK application caused an increase in the non-available P fraction (HCl-Pi), while the use of NPKEC decreased the HCl-Pi concentration in all cropping systems, suggesting stronger merits both for intercropping and NPKEC. Surprisingly, maize exhibited substantially higher phosphatases activity compared to cowpea in monoculture amended with compost, implying distinct crop strategies for adaptation under low P conditions. Based on the multi-factor analysis, the close association of NaHCO3–P with P solubilizing bacteria, root carboxylates and pH indicated that rhizosphere processes are the strongest predictors of immediately available P. Since alkaline phosphatase (ALP) is a P-degrading enzyme of microbial origin, rhizosphere related ALP association may have originated from root-associated microflora promoting P mobilization. Furthermore, the strong association of microbial biomass P (MBP) and acid phosphates (ACP) with NaOH–P fraction indicated moderately available P cycle in soil was mainly driven by microbial-related processes. Factor analysis map and two-way ANOVA confirmed that fertilization regime had a stronger effect on all tested variables compared to cropping system. Altogether, our results suggest that a combination of microbial-rhizosphere processes controls the dynamics of P fertility in semi-arid soils. In the broader context of improving soil P fertility, it is highly recommended the use of environmentally sustainable sources of fertilizer, such as NPKEC, which can enhance the competitive performance of legume-cereal intercropping under semi-arid agroecosystems.



中文翻译:

在半干旱农业生态系统中,耕作制度和施肥方式对土壤磷的影响是通过根际-微生物过程介导的。

在半干旱地区,谷物-豆类间作中的土壤磷(P)动态尚未得到充分阐明,特别是在肥料的综合施用方面。为此,我们研究了不同肥料对a豆/玉米间作系统中根际-微生物过程的影响。连续两年(2016-2017)在分田设计中进行了田间试验,方法是单独建立cow豆/玉米,或在主田间作,将cow豆/玉米间作,而对副田进行四种施肥处理,即不添加肥料(控制),有机改良剂(堆肥),矿物肥料(NPK)和富含多种营养的堆肥(NPKEC)。我们的结果表明,NPKEC肥料增加了NaHCO 3 -P i与对照地相比,玉米高69%,pea豆为62%,间作地为93%。同样,NPKEC处理的所有农作系统中NaHCO 3 -P o分数也显着增加。在中等不稳定的P情况下,NPKEC肥料在间作地块中造成NaOH-P o(12.87±0.50 mg P kg -1土壤)和NaOH-P i(22.29±0.83 mg P kg -1土壤)增幅最大。除了间作,NPK应用引起在非有效P分数(HCL-P的增加),而使用NPKEC的降低的HCl-P在所有种植系统中均表现出较高的集中度,这表明间作和NPKEC均具有更强的优势。出乎意料的是,与用堆肥改良的单一栽培中的cow豆相比,玉米表现出明显更高的磷酸酶活性,这暗示了在低磷条件下适应的独特作物策略。基于多因素分析,NaHCO 3的紧密缔合-P与P增溶细菌,根羧酸盐和pH值表明,根际过程是立即可用P的最强预测因子。由于碱性磷酸酶(ALP)是微生物来源的P降解酶,根际相关的ALP缔合可能起源于根相关微生物促进磷动员。此外,微生物生物量磷(MBP)和酸性磷酸盐(ACP)与NaOH-P组分的强相关性表明土壤中适度可用的磷循环主要由微生物相关过程驱动。因子分析图和双向方差分析证实,与种植系统相比,施肥制度对所有测试变量的影响更大。总之,我们的结果表明,微生物-根际过程的组合控制了半干旱土壤中磷的肥力动态。

更新日期:2020-07-08
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