Frontiers of Agricultural Science and Engineering
Cover Story   2019, Volume 6 Issue 4
Phosphorous is a nutritional element essential for all living organisms. However, phosphate rock reserves are limited and unevenly distributed worldwide. Despite this limitation, current phosphate use is highly inefficient with open cycles causing severe environmental problems. Both the environmental problems and the exhaustion of global phosphate [Detail] ...
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, Volume 6 Issue 4

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Adaptation of Chinese and German maize-based food-feed-energy systems to limited phosphate resources—a new Sino-German international research training group
Torsten MÜLLER, Fusuo ZHANG
Front. Agr. Sci. Eng. . 2019, 6 (4): 313-320.

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Phosphate is supplied to agriculture by mining and fertilizer production, followed by different steps of phosphate utilization, including primary production, feed and food consumption, and conversion of biomass, with accumulation in soils, but little recycling and severe environmental losses. Phosphate is a limited essential nutrient, however, with very uneven distribution worldwide. Closing the cycle and reducing primary phosphate consumption are fundamental future challenges. Maize has a relatively high phosphate requirement. China and Germany together cover the whole range of maize production systems. The new Sino-German international research training group “Adaptation of Chinese and German maize-based food-feed-energy systems to limited phosphate resources” (AMAIZE-P) was initiated in 2018 as a joint venture of the China Agricultural University (Beijing, China) and the University of Hohenheim (Stuttgart, Germany). The interdisciplinary and complementary research is driven by the hypothesis that under phosphate limited conditions, high productivity and high phosphate use efficiency can be achieved simultaneously by adapting phosphate cycling and availability (sources) to the multipurpose phosphate demands (sinks) in maize-based food-feed-energy systems. The educational program for doctoral researchers in China and Germany includes joint block seminars, thematic field trips, case studies, methodological courses, doctoral researchers’ conferences, intercultural training sessions and personal training.

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Innovations of phosphorus sustainability: implications for the whole chain
Jianbo SHEN, Liyang WANG, Xiaoqiang JIAO, Fanlei MENG, Lin ZHANG, Gu FENG, Junling ZHANG, Lixing YUAN, Lin MA, Yong HOU, Tao ZHANG, Weifeng ZHANG, Guohua LI, Kai ZHANG, Fusuo ZHANG
Front. Agr. Sci. Eng. . 2019, 6 (4): 321-331.

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Phosphorus (P) is a non-renewable resource, therefore ensuring global food and environmental security depends upon sustainable P management. To achieve this goal, sustainable P management in the upstream and downstream sectors of agriculture from mineral extraction to food consumption must be addressed systematically. The innovation and feasibility of P sustainability are highlighted from the perspective of the whole P-based chain, including the mining and processing of P rock, production of P fertilizers, soil and rhizosphere processes involving P, absorption and utilization of P by plants, P in livestock production, as well as flow and management of P at the catchment scale. The paper also emphasizes the importance of recycling P and the current challenges of P recovery. Finally, sustainable solutions of holistic P management are proposed from the perspective of technology improvement with policy support.

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Phosphorus use efficiency and fertilizers: future opportunities for improvements
Front. Agr. Sci. Eng. . 2019, 6 (4): 332-340.

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The continued supply of phosphate fertilizers that underpin global food production is an imminent crisis. The rock phosphate deposits on which the world depends are not only finite, but some are contaminated, and many are located in geopolitically unstable areas, meaning that fundamental changes will have to take place in order to maintain food production for a growing global population. No single solution exists, but a combination of approaches to phosphorus management is required not only to extend the lifespan of the remaining non-renewable rock phosphate reserves, but to result in a more efficient, sustainable phosphorus cycle. Solutions include improving the efficiency of fertilizer applications to agricultural land, alongside a better understanding of phosphorus cycling in soil-plant systems, and the interactions between soil physics, chemistry and biology, coupled with plant traits. Opportunities exist for the development of plants that can access different forms of soil phosphorus (e.g., organic phosphorus) and that use internal phosphorus more efficiently. The development of different sources of phosphorus fertilizers are inevitably required given the finite nature of the rock phosphate supplies. Clear opportunities exist, and it is now important that a concerted effort to make advances in phosphorus use efficiency is prioritized.

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Strategies for improving fertilizer phosphorus use efficiency in Chinese cropping systems
Gu FENG, Jingping GAI, Xionghan FENG, Haigang LI, Lin ZHANG, Keke YI, Jialong LV, Yiyong ZHU, Li TANG, Yilin LI
Front. Agr. Sci. Eng. . 2019, 6 (4): 341-347.

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A four-year project, entitled “The mechanisms of fraction transformation and high use efficiency of P fertilizer in Chinese cropping systems” commenced in 2017. The project was established to answer three key questions and looked at 17 cropping systems on ten soils. First, we asked what are the dynamics of transformation, fixation and mobilization of P fertilizers in soil-cropping systems? Second, what are the mechanisms of soil-crop-microbe interactions by which P fertilizer can be efficiently used? Third, how to manipulate the processes of P use in cropping systems? The targets of this project are (1) to explore the mechanisms of P fixation, the pathways of loss of P availability and the threshold of migration of fertilizer P in the field; (2) to uncover mechanisms by which soil legacy P is mobilized through root physiological and morphological processes and through arbuscular mycorrhizal fungi and P-solubilizing bacteria in rhizosphere and hyphosphere; (3) to estimate the biological potential of crops for high efficiency P absorption and use; (4) to innovate new approaches for improving the efficiency of P fertilizers. The outcomes will provide theoretical support for setting standards for limitation of P fertilizer application rate in the main cropping zones of China.

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Phosphorus supply and management in vegetable production systems in China
Rui WANG, Weiming SHI, Yilin LI
Front. Agr. Sci. Eng. . 2019, 6 (4): 348-356.

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Vegetable production systems involve high rates of chemical and organic fertilizer applications, leading to significant P accumulation in vegetable soils, as well as a decrease in P use efficiency (PUE), which is one of the key limiting factors in vegetable production. This review introduces the vegetable production systems in China and their fertilization status, and analyzes probable causes of overfertilization of vegetable fields. Poorly developed root systems and high P demand have led to the need to maintain much higher available P concentrations in the root zone for regular growth of vegetables, which might necessitate higher phosphate fertilizer input than the plants require. Research on strategies to improve vegetable PUE and the mechanisms of these strategies are summarized in this review. Increasing the P uptake by vegetables by supplying P during the critical growth stage and effectively utilizing the accumulated P by optimizing the C:P ratio in soils can substantially increase PUE. These advances will provide a basis for improving PUE and optimizing phosphate fertilizer applications in vegetable production through regulatory measures. In addition, some policies are recommended that could ensure the safety of vegetables and improve product quality. This review also aims to improve understanding of P cycling in vegetable fields and assist in the development of best practices to manage P reserves globally.

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Improving the efficiency and effectiveness of global phosphorus use: focus on root and rhizosphere levels in the agronomic system
Front. Agr. Sci. Eng. . 2019, 6 (4): 357-365.

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Phosphorus (P) is essential for life and for efficient crop production, but global P use with limited recycling is inefficient in several sectors, including agronomy. Unfortunately, plant physiologists, agronomists, farmers and end users employ different measures for P use efficiency (PUE), which often masks their values at different scales. The term P use effectiveness, which also considers energetic and sustainability measures in addition to P balances, is also a valuable concept. Major physiological and genetic factors for plant P uptake and utilization have been identified, but there has been limited success in genetically improving PUE of modern crop cultivars. In maize, studies on root architectural and morphological traits appear promising. Rhizosphere processes assist in mobilizing and capturing sparingly soluble phosphate from rock phosphate. Combinations of phosphate-solubilizing microorganisms with ammonium-based nitrogen fertilizer, as well as strategies of fertilizer placement near the roots of target crops, can moderately enhance PUE. The desired concentration of P in the products differs, depending on the final use of the crop products as feed, food or for energy conversion, which should be considered during crop production.

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Genetic study and molecular breeding for high phosphorus use efficiency in maize
Dongdong LI, Meng WANG, Xianyan KUANG, Wenxin LIU
Front. Agr. Sci. Eng. . 2019, 6 (4): 366-379.

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Phosphorus is the second most important macronutrient after nitrogen and it has many vital functions in the life of plants. Most soils have a low available P content, which has become a key limiting factor for increasing crop production. Also, low P use efficiency (PUE) of crops in conjunction with excessive application of P fertilizers has resulted in serious environmental problems. Thus, dissecting the genetic architecture of crop PUE, mining related quantitative trait loci (QTL) and using molecular breeding methods to improve high PUE germplasm are of great significance and serve as an efficient approach for the development of sustainable agriculture. In this review, molecular and phenotypic characteristics of maize inbred lines with high PUE, related QTL and genes as well as low-P responses are summarized. Based on this, a breeding strategy applying genomic selection as the core, and integrating the existing genetic information and molecular breeding techniques is proposed for breeding high PUE maize inbred lines and hybrids.

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Phytate and phosphorus utilization by broiler chickens and laying hens fed maize-based diets
Qiugang MA, Markus RODEHUTSCORD, Moritz NOVOTNY, Lan LI, Luqing YANG
Front. Agr. Sci. Eng. . 2019, 6 (4): 380-387.

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Maize grain is primarily used as an energy source for poultry and other animals. Maize has relatively high phytate-P content and very low intrinsic phytase activity. Given that feed phosphates are produced from finite rock phosphate resources, a reduction in the use of feed phosphates in maize-based diets by increasing the utilization of plant P sources by animals is necessary to make poultry meat and egg production more sustainable. The utilization of P by poultry is affected by two intrinsic characteristics of maize: the concentration of inositol phosphates and the activity of the intrinsic phytase of the grain in the digestive tract. The objective of this review is to present data on the variation that exists in composition of maize relevant for P use and to address factors that influence P utilization in maize-based diets of poultry. Broiler chickens and laying hens have the potential to degrade phytate in the gastrointestinal tract, but this is depressed by high dietary Ca and P concentrations. Published values of phytate degradation in broilers are overall higher than those in laying hens. Differences also exist between broiler chickens and growing turkeys and Pekin ducks. The exogenous supplementation of microbial phytases and the introduction of transgenic high phytase maize in poultry diets are efficient not only for the improvement of phytate-P digestibility, production performance, egg quality and bone mineralization, but also for the reduction of P excreta to control environmental impact.

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Phosphorus status, use and recycling in a Chinese peri-urban region with intensive animal husbandry and cropping systems Results from case study in a Sino-German applied research collaboration project
Marco ROELCKE, Lisa HEIMANN, Yong HOU, Jianbin GUO, Qiaoyun XUE, Wei JIA, Anne OSTERMANN, Roxana Mendoza HUAITALLA, Moritz ENGBERS, Clemens OLBRICH, Roland W. SCHOLZ, Joachim CLEMENS, Frank SCHUCHARDT, Rolf NIEDER, Xuejun LIU, Fusuo ZHANG
Front. Agr. Sci. Eng. . 2019, 6 (4): 388-402.

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The Sino-German research collaboration project, “Recycling of organic residues from agricultural and municipal origin in China” (2008–2012), comprising different interdisciplinary research groups, and also German small and medium-sized enterprises, aimed at developing integrated strategies and solutions for the recycling of organic residues in China. In an intensive crop-livestock agricultural region in the Shunyi District of Beijing, five typical cropping systems were investigated. The research was conducted in the form of analyses of phosphorus (P) in soil, plants, animal feed, animal products, manures, mineral and organic fertilizers and the derivation of the corresponding nutrient balances and P flows. The mean annual P balance surplus was 492 kg·ha1·yr1 P for the vegetable production system, significantly higher (P<0.05) than that for orchards (130 kg·ha1·yr1P) and cereal crops (83 kg·ha1·yr1 P). Plant-available P (Olsen-P) concentrations of topsoils (0–20 cm) had good correlations with the amounts of P applied (from mineral and organic sources). Compared to results from the Second Chinese National Soil Survey of 1981, mean concentrations of available P in soils of 19 plots investigated in Shunyi District increased 10-fold (from 7.3 to 60 mg·kg1) from 1981 to 2009. On average, the critical limit for Olsen-P concentrations (>30 mg·kg1) that can lead to increased risk of P loss was exceeded in all five cropping systems. With feed additives, the “natural background value” (Chinese Environmental Quality Standard for Soils) of copper and zinc in topsoils was exceeded at several sites. Screening for several substances in the veterinary antibiotic classes of sulfonamides, tetracyclines, and fluoroquinolones revealed widespread topsoil contamination. Calculated livestock densities were 10.6 livestock units per ha arable land in 2007. Animal husbandry is increasingly conducted in large operations, making traditional ways of reuse difficult to apply. Comparing three management systems for treatment of organic residues from a pig farm via aerobic (composting) or anaerobic (biogas) treatment in a life cycle assessment, the resulting cropland demand for a sustainable land application of biogas effluent varied between 139 and 288 ha·yr1, well above the cropland area owned by the farm (10 ha). The mismatch problems in the above context between business-as-usual and improving performance are framed and discussed as (1) the mismatch between centralized animal husbandry and smallholder farming, (2) the mismatch between livestock density and cropland, (3) nutrient (including P) recycling and increasing organic matter content versus energy production, (4) subsidies for compost production and biogas, as well as (5) advances in the regulatory framework in China.

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The current phosphate recycling situation in China and Germany: a comparative review
Qing XUE, Xinyue HE, Saskia D. SACHS, Gero C. BECKER, Tao ZHANG, Andrea KRUSE
Front. Agr. Sci. Eng. . 2019, 6 (4): 403-418.

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Phosphorus (P) is an indispensable element for organisms but the primary source of P—mineral phosphate resources—are non-renewable. Agricultural production has a high demand for fossil phosphate resources, but the resulting phosphate-rich residues are lack of management. This leads to rapid reserves depletion and severe phosphate pollution risks. One sustainable way is to reuse the phosphate dispersed in various residues such as sewage sludge and livestock manure. Diverse techniques have emerged to recover phosphate from wastes to close the phosphate cycle. While it is a global issue, the regional situations regarding potential phosphate scarcity and its management differ strongly. China is rich in phosphate resources, but over-exploitation has greatly increased the risk of phosphate rocks depletion, while in Germany the P resources depend on imports, but there is commitment to keep a balance between import and utilization. This had led to great differences in the way the two countries deal with the “re-use” of phosphate in waste. China is now in a transition phase from the simple terminal pollution control to “waste” reuse and nutrient resources recycling. One sign of this tendency is the mandatory garbage classification and preparation for further processing and recycling. This was first implemented in Shanghai in 2019, whereas Germany has been following the legal framework for waste management since the 19th century. There are a series of laws to control the nutrient loss from municipal and agricultural activities, as for instance with sewage sludge ordinance and fertilizer legislation. Many of these laws have been newly revised recently. Sewage sludge cannot be directly utilized on farmland as organic fertilizer any more. Alternatively, phosphate and other nutrients should be recovered from sewage sludge. Advanced phosphate recovery technologies and related nutrient recycling schemes are proceeding. This review summarizes the current situation of phosphate-containing residues management and phosphate reuse in China and Germany. The state legislation and policies, which would affect the phosphate recycling concept are presented as well. As there are various kinds of phosphate-containing residues, different phosphate recovery technologies can be applied. Those technologies are discussed from their mechanism and suitability.

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Cadmium pollution from phosphate fertilizers in arable soils and crops: an overview
Andrea Giovanna NIÑO-SAVALA, Zhong ZHUANG, Xin MA, Andreas FANGMEIER, Huafen LI, Aohan TANG, Xuejun LIU
Front. Agr. Sci. Eng. . 2019, 6 (4): 419-430.

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The application of mineral and organic phosphorus fertilizers to arable land has greatly increased crop yield to meet the world food demand. On the other hand, impurities in these fertilizers, such as heavy metals, are being added to agricultural soils, resulting both from the raw materials themselves and the processes used to obtain the final product. Cadmium, a non-essential and toxic heavy metal, has been found in relatively high amounts in common P fertilizers obtained from sediments. This metal poses a high risk for soil fertility, crop cultivation, and plants in general. Furthermore, human health might be compromised by the cadmium concentrations in agricultural and livestock products, due to the bioaccumulation effect in the food web. The accumulation in the different matrixes is the result of the high mobility and flexible availability of this harmful metal. This review summarizes risks to human health, the factors influencing cadmium movement in soils and crop uptake, as well as common plant responses to its toxicity. In addition, it summarizes cadmium balances in soils, trends, long-term experiments, and further studies. Cadmium inputs and outputs in arable soil, together with their calculated concentrations, are compared between two different regions: the European countries (in particular Germany) and China. The comparison appears useful because of the different proportions in the inputs and outputs of cadmium, and the diverse geographical, environmental and social factors. Moreover, these variables and their influences on cadmium contamination improve the understanding of the pollution from phosphate fertilizers and will help to establish future mitigation policies.

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Comparison of analytical procedures for measuring phosphorus content of animal manures in China
Guohua LI, Qian LIU, Haigang LI, Fusuo ZHANG
Front. Agr. Sci. Eng. . 2019, 6 (4): 431-440.

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The concentration and components of manure phosphorus (P) are key factors determining potential P bioavailability and runoff. The distribution of P forms in swine, poultry and cattle manures collected from intensive and extensive production systems in several areas of China was investigated with sequential fractionation and a simplified two-step (NaHCO3-NaOH/EDTA) procedures. The mean total P concentration, determined by the sequential fractionation procedure of intensive swine, poultry and cattle manure, expressed as g·kg1, was 14.9, 13.4 and 5.8 g·kg1, respectively, and 4.4 g·kg1 in extensive cattle manure. In intensive swine, poultry and cattle manure about 73%, 74% and 79% of total P, respectively, was bioavailable (i.e., P extracted by H2O and NaHCO3) and 78% in extensive cattle manure. The results indicated the relative environmental risk, from high to low, of swine, poultry and cattle manure. There is considerable regional variation in animal manure P across China, which needs to be considered when developing manure management strategies.

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15 articles