Towards Sustainable Dairy Production in Argentina: Evaluating Nutrient and CO2 Release from Raw and Processed Farm Waste

Mineralization studies are the first step in determining the usefulness of an amendment such as fertilizer, and are essential to creating guidelines for dairy waste management to help producers make informed decisions. Our goal was to assess the effects of dairy raw, composted, and digested manure amendments on C, N, and P mineralization to evaluate the feasibility of their in-farm production and use as organic fertilizers. The liquid and solid fractions of dairy effluent (LDE, SDE), dairy effluent digestate (DED), onion–cattle manure digestate and compost (OCMD, OCMC) were characterized by chemical and spectroscopic methods. Soil microcosms with LDE, SDE, DED, OCMD and OCMC and the C, N and P mineralization were determined periodically. Elemental and structural differences among amendments led to contrasting profiles of C, N, and P mineralization, and thus to differences in nutrient availability, immobilization, and CO2 emission. All processed materials were more stable than untreated waste, reducing C emissions. Digestates showed net C immobilization, and supplied the highest levels of available N, creating a relative P deficit. Instead, the compost supplied N and P via mineralization, producing a relative P excess. Future studies should aim at evaluating fertilization strategies that combine both kinds of amendments, to exploit their complimentary agronomic characteristics.

Nitrogen species specific phosphorus mineralization in temperate floodplain soils

As an essential component of enzymes, higher N availability from agricultural runoff to forest soils may boost the activity of phosphatase, increasing the bioavailability of phosphate. The objective of this study was to evaluate P mineralization rates in temperate floodplain soils as a function of inorganic N species (i.e., ammonium and nitrate) and amendment rate (1.5–3.5 g N kg−1). Accordingly, the soil was amended with nitrate and ammonium, and P dynamics were monitored during a 40-day incubation. The addition of ammonium significantly boosted acid and alkaline phosphatase activity by 1.39 and 1.44 µmol p-nitrophenol P (pNP) g−1 h−1, respectively. The degree of increase was positively correlated with the amendment rate. Likewise, the P mineralization rate increased by 0.27 mg P kg−1 in the 3.5 g N kg−1 ammonium treatment. 31P nuclear magnetic resonance spectroscopic analysis further supported the reduction in organic orthophosphate diesters on day 30. Meanwhile, the addition of nitrate promoted P mineralization to a lesser degree but did not increase phosphatase activity. While floodplain soils have great potential to sequester anthropogenic P, high availability of inorganic N, especially ammonium, could promote P mineralization, potentially increasing P fertility and/or reducing P the sequestration capacity of floodplain soils.

Warming drives sustained plant phosphorus demand in a humid tropical forest

Phosphorus (P) is often one of the most limiting nutrients in highly weathered soils of humid tropical forests, which may regulate the responses of carbon (C) feedback to climate warming. Based on a 7-year continuous field warming experiment conducted by translocating microcosm forest ecosystems from a high-elevation site to low-elevation sites, we detected changes in the ecosystem P cycle in response to warming. We report that warming drives sustained plant P demand by increasing P uptake and thus decreasing foliar N:P. This increased plant P content is supplied by multiple processes including enhanced plant P resorption, soil P mineralization and dissolution without changing litter P mineralization and leachate P. These findings suggest that warming may alleviate initial P deficiency and/or limitation of plant growth and contribute to sustaining plant C fixation in these tropical forests.

The Role of Biochar in Regulating the Carbon, Phosphorus, and Nitrogen Cycles Exemplified by Soil Systems

Biochar is a carbon-rich material prepared from the pyrolysis of biomass under various conditions. Recently, biochar drew great attention due to its promising potential in climate change mitigation, soil amendment, and environmental control. Obviously, biochar can be a beneficial soil amendment in several ways including preventing nutrients loss due to leaching, increasing N and P mineralization, and enabling the microbial mediation of N2O and CO2 emissions. However, there are also conflicting reports on biochar effects, such as water logging and weathering induced change of surface properties that ultimately affects microbial growth and soil fertility. Despite the voluminous reports on soil and biochar properties, few studies have systematically addressed the effects of biochar on the sequestration of carbon, nitrogen, and phosphorus in soils. Information on microbially-mediated transformation of carbon (C), nitrogen (N), and phosphorus (P) species in the soil environment remains relatively uncertain. A systematic documentation of how biochar influences the fate and transport of carbon, phosphorus, and nitrogen in soil is crucial to promoting biochar applications toward environmental sustainability. This report first provides an overview on the adsorption of carbon, phosphorus, and nitrogen species on biochar, particularly in soil systems. Then, the biochar-mediated transformation of organic species, and the transport of carbon, nitrogen, and phosphorus in soil systems are discussed. This review also reports on the weathering process of biochar and implications in the soil environment. Lastly, the current knowledge gaps and priority research directions for the biochar-amended systems in the future are assessed. This review focuses on literatures published in the past decade (2009–2021) on the adsorption, degradation, transport, weathering, and transformation of C, N, and P species in soil systems with respect to biochar applications.

Effect of Two Different Sugarcane Cultivars on Rhizosphere Bacterial Communities of Sugarcane and Soybean Upon Intercropping

Intercropping of soybean and sugarcane is an important strategy to promote sustainable development of the sugarcane industry. In fact, our understanding of the interaction between the rhizosphere and bacterial communities in the intercropping system is still evolving; particularly, the influence of different sugarcane varieties on rhizosphere bacterial communities in the intercropping process with soybean, still needs further research. Here, we evaluated the response of sugarcane varieties ZZ1 and ZZ9 to the root bacterial community during intercropping with soybean. We found that when ZZ9 was intercropped with soybean, the bacterial diversity increased significantly as compared to that when ZZ1 was used. ZZ9 played a major role in changing the bacterial environment of the root system by affecting the diversity of rhizosphere bacteria, forming a rhizosphere environment more conducive to the growth of sugarcane. In addition, our study found that ZZ1 and ZZ9 had differed significantly in their utilization of nutrients. For example, nutrients were affected by different functional genes in processes such as denitrification, P-uptake and transport, inorganic P-solubilization, and organic P-mineralization. These results are significant in terms of providing guidance to the sugarcane industry, particularly for the intercropping of sugarcane and soybean in Guangxi, China.

Nitrogen addition accelerates ecosystem phosphorus cycling at multiple scales in a temperate grassland of Northeast China

<p>Plant phosphorus (P) resorption, mutualistic symbiosis with mycorrhizas, such as arbuscular mycorrhizal fungi (AMF) and soil organic P mineralization are crucial strategies for acquiring sufficient P to meet plant nutrient demand. Which is the main strategy, however, responding to elevated nitrogen (N) addition to alleviate P deficiency caused by N enrichment remains unclear in terrestrial ecosystems. We explored the responses of foliar P resorption of dominate species (Leymus chinensis), soil microbial properties and organic P mineralization to multi-level N addition in a temperate meadow steppe, Northeast China. We found the enhancements in plant biomass, microbial biomass C and N (MBC, MBN), alkaline phosphatase activities (ALP), and phoD gene abundance (main gene coded soil ALP), while the reductions in soil pH, available P, microbial biomass P, and AMF abundance, and no significant responses of foliar P content under simulative N deposition. When the rates exceeded the threshold 10 g N m<sup>-2</sup>yr<sup>-1</sup>, plants and microbes had little additional responses to N enrichment. Notably, N addition had distinct effects on three plant P acquisition strategies, that no conspicuous increase in P resorption efficiency, reduced dependence on mutualistic with AMF symbiosis and accelerated organic P mineralization. A positive correlation between ALP activity, phoD gene abundance and P mineralization rate suggested increases in phosphatase activities and its functional gene copies play crucial roles in organic P mineralization. Nitrogen addition aggravated P deficiency to the production of plant and microbial biomass, which further accelerated soil organic P mineralization and foliar P resorption. Due to lack of plasticity in P resorption efficiency and reduced dependence on mutualistic with AMF symbiosis, however, the organic P mineralization dominated in P acquisition to meet increased P demand. Furthermore, the increase in ALP activities, activation of phoD genes and decrease in soil pH were the main pathways to accelerate organic P mineralization and consequently alleviated P deficiency caused by anthropogenic N deposition, especially at conditions of N saturation. Our results provide strong evidences that N addition can accelerate the rate of P cycling and mobilize plant P uptake strategies such as soil organic P mineralization and leaf P resorption, which are important to better maintain sustainable ecosystem development in the more fertilized word.</p><p>Acknowledgments: This work was supported by the National Key Research and Development Program of China (2016YFC0500602), National Natural Science Foundation of China (31570470, 31870456), the Fundamental Research Funds for the Central Universities (2412018ZD010), and the Program of Introducing Talents of Discipline to Universities (B16011). H.C. acknowledges support from Chinese Scholarship Council (CSC).</p>

Controls over phosphorus mineralization and immobilization rates in different tropical soils

<p>Highly weathered soils depleted in minerals and phosphorus (P) support large tracts of the tropical rainforests in the Central Amazon, which significantly contribute to the global carbon (C) sink. In these soils (oxisols and ferrasols), P is either occluded in Al/Fe-oxides, bound to the soil mineral matrix or in soil organic matter, and therefore not directly available for uptake as inorganic phosphate (Pi). To liberate Pi for plant or microbial uptake two processes are key: (i) changes of sorption-desorption equilibria of Pi with the soil matrix and (ii) the release of Pi from organic compounds (Po) catalyzed by enzymes, such as phosphatases. Plant roots and soil microbes have developed strategies to stimulate the release of P by accelerating P dissolution and desorption and by releasing extracellular phosphatases into the soil environment, which requires however C and energy investment. Because of P limitation in this ecosystem, the relative contributions of abiotic and biotic controls over P mineralization is of pivotal importance. Yet conclusive results are still scarce.</p><p>We therefore aimed to disentangle abiotic and biotic controls over P mineralization in tropical soils. To achieve this, we collected forest soils from the Amazon Basin covering a range of soil texture and P concentrations, determined soil mineralogy and measured gross P desorption and mineralization rates using a <sup>33</sup>P isotope pool dilution assay. Moreover, we determined acid phosphatase activity rates and microbial biomass C and P. We found significant differences between the studied sites in gross P influx and efflux rates into the Pi pool. Gross influx rates (i.e. the sum of Pi desorption and organic P mineralization) exceeded efflux (i.e. sorption or biotic Pi uptake rates) only in sandy and silty soils, while in clayey soils efflux rates dominated P fluxes indicating a very high Pi sorption capacity. However, gross influx and efflux rates were not related to total or dissolved P. Microbial biomass and acid phosphatase activity normalized to microbial biomass C were highest in sites with overall low total P microbial biomass P accounting for up to 40 % of total P in low P soils. We therefore conclude that in low P soils organic P turnover plays a major role in soil P cycling, and despite of the high P sorption capacity of clay rich soils, microbes can be strong competitors for plant available P.</p>

Continental scale climate, land-use and geological controls of soil P cycling and relations with soil C and N

<p>Despite the importance of phosphorus (P) as a nutrient for all life, its availability is highly constrained in terrestrial ecosystems. The availability of P to plants and microbes is regulated by abiotic processes (e.g. P sorption/desorption, precipitation/dissolution) and biological activities (microbial P immobilization/organic P mineralization). Due to the strong geochemical component of the P cycle, it can be expected that soil C, N and P cycling may differ in terms of effects of geology, climate and management. Despite advances in our understanding of physico-chemical controls on P availability, there is still little mechanistic understanding of large scale controls on soil P cycling and its relation to soil C and N cycling, due to a lack of broad scale studies using common methodologies.</p><p>Here we aimed to investigate soil physicochemical and biological factors that drive soil P cycling and may cause a (de)coupling of C, N and P processes. We therefore sampled mineral topsoils (0-10 cm, n=95) across a continental transect in Europe (Southern Spain to Northern Scandinavia), covering major geological, climatic and land use gradients. The soils derived from different land uses (cropland, grassland, forest/woodland) and bedrock types (silicate, sediment, calcareous). We analyzed a wide range of potentially relevant physico-chemical and biological properties and measured gross rates of soil N and P processes by short term (24 h) incubations of soils with <sup>33</sup>P and <sup>15</sup>N following isotope pool dilution approaches.</p><p>(i) Across the whole transect land-use effects on soil P pools and processes exceeded those of geology, reflecting the accumulation of fertilizer P in soils of managed ecosystems. Cropland (and grasslands) had higher values of soil total P and soil inorganic P (Pi), available Pi (Olsen P), and gross Pi mobilization rates by abiotic and biotic processes compared to forests. Soil phosphatase activity did not vary between land-uses. Soils on silicate bedrock had significantly higher total and labile P than calcareous soils.</p><p>(ii) Climate differentially affected P pools and processes. Soil total P, dissolved organic P, and gross Pi desorption decreased with mean annual temperature (MAT; these properties were not sensitive to mean annual precipitation - MAP), while soil phosphatase activity and gross total Pi mobilization through abiotic and biotic processes increased with MAP but were insensitive to MAT. This clearly points to adverse climatic controls of biotic and abiotic soil P processes.</p><p>(iii) We found strong interlinkages between soil C, N and P pools (soil organic matter and microbial biomass) and soil enzymes (beta-glucosidase, chitinase, phosphatase) but not in related gross processes (respiration, N and P mineralization). Interestingly the slopes of C-P and N-P relations of pools and enzymes differed systematically between land-uses, indicating that land management causes a partial decoupling of P from C and N cycles, reflecting the P-richness of croplands.</p>