Nitrogen deposition to land from the atmosphere

The use of maize for livestock feeding in the United Kingdom

A change in land use from agriculture to forest generally increases soil acidity. However, it remains unclear to what extent plant traits can enhance or mitigate soil acidification caused by atmospheric deposition. Soil acidification is detrimental for the survival of many species. An in‐depth understanding of tree species‐specific effects on soil acidification is therefore crucial, particularly in view of the predicted global increases in acidifying nitrogen ( N ) deposition. Here, we report soil acidification rates in a chronosequence of broadleaved deciduous forests planted on former arable land in Belgium. This region receives one of the highest loads of potentially acidifying atmospheric deposition in Europe, which allowed us to study a ‘worst case scenario’. We show that less than four decades of forest development caused significant soil acidification. Atmospheric deposition undoubtedly and unequivocally drives postagricultural forests towards more acidic conditions, but the rate of soil acidification is also determined by the tree species‐specific leaf litter quality and litter decomposition rates. We propose that the intrinsic differences in leaf litter quality among tree species create fundamentally different nutrient cycles within the ecosystem, both directly through the chemical composition of the litter and indirectly through its effects on the size and composition of earthworm communities. Poor leaf litter quality contributes to the absence of a burrowing earthworm community, which retards leaf litter decomposition and, consequently, results in forest‐floor build‐up and soil acidification. Also nutrient uptake and N 2 fixation are causing soil acidification, but were found to be less important. Our results highlight the fact that tree species‐specific traits significantly influence the magnitude of human pollution‐induced soil acidification.

The study examined the impact of deforestation and subsequent cultivation on soil fertility and acidity conditions under varying soil depths. Soil profiles were opened in two adjacent land units, namely forestland and arable land and samples were collected from genetic horizons. Deterioration of soil fertility was observed after deforestation and traditional cultivation. The main aim of deforestation was agricultural expansion. Soil pH consistently decreased with depth in both land units and it was relatively lowest in arable land perhaps due to depletion of organic matter (OM) and decrease in buffering capacity of the soil. The OM and total nitrogen (N) ranged from 0.78 and 0.06% in the 75 to160 cm layer of arable land to 15 and 0.61% in the 0 to10 cm layer of forestland, respectively. Total N was strongly and positively correlated with soil OM (r = 0.99). Exchangeable Al was poorly and negatively correlated with available phosphorous (r = -0.41). Conversion of forestland to arable land reduced the mean available phosphorus (P) from 4.04 ppm to 1.95 ppm most probably due to decline in OM, soil acidification and erosion. Deforestation and subsequent continuous cultivation over the past 25 years apparently amplified the mean exchangeable acids from 0.83 cmol (+) kg-1 to 5.96 cmol (+) kg-1. Soil acidification and related problems were the major challenges of continuous cultivation in the study area. The study indicated that land use change and management practices have had a considerable negative effect on soil physical and chemical properties. Key words: Deforestation, continuous cultivation, land use change, soil properties, soil fertility, soil acidity, Western Ethiopia.

Nitrate and water supplies in the United Kingdom

Biochar has been considered as a promising soil amendment for improving fertility and mitigating N2O emission from the arable land. However, biochar's effectiveness in acidic tea soil and underlying mechanisms are largely unknown. We conducted a short-term microcosm experiment using two biochars (1% w/w, LB, generated from legume and NLB, non-legume biomass, respectively) to investigate the effects of biochar amendments on soil chemical properties, N2O emission, and microbial community in an acidic soil. Soil and headspace gas samples were taken on 1, 10, and 30 day's incubation. Biochar amendment increased soil pH and DOC, however, significantly reduced soil inorganic N. Both biochars at ~ 1% addition had little effect on microbial CO2 respiration but suppressed soil N2O emission by ~ 40% during the incubation. The divergence in N2O efflux rates between soils with and without biochar addition aligned to some degree with changes in soil pH, inorganic N, and dissolved organic C (DOC). We also found that biochar addition significantly modified the fungal community structure, in particular the relative abundance of members of Ascomycota, but not the bacterial community. Furthermore, the copy number of nosZ, the gene encoding N2O reductase, was significantly greater in biochar-amended soils than the soil alone. Our findings contribute to better understanding of the impact of biochar on the soil chemical properties, soil N2O emission, and microbial community and the consequences of soil biochar amendment for improving the health of acidic tea soil.

The lime–silicate question

Soil degradation is the primary restriction affecting many developing countries' agricultural systems. Ethiopia is a developing country in horn Africa that is severely challenged by soil degradation issues. The main processes of soil deterioration are acidification and salinization. Furthermore, soil acidity is one of the primary reasons obstructing and preventing lucrative and sustainable agricultural productivity in many African countries as well as many other regions of the world. Soil acidity problems have hampered sustainable agricultural productivity in practically all productive areas in Ethiopia. The main goal of the seminar is to highlight the problems of soil acidity to agricultural production in Ethiopia's highlands, as well as management strategies for alleviating soil acidity and increasing crop output. Soil acidity affects over half of Ethiopia's arable land. Strong acid soils cover more than half of the arable land affected by soil acidity. Researchers discovered two primary reasons that limit acidic soil fertility: the presence of phytotoxicity substances and nutrient shortage. Numerous strategic soil acid management plans have been created to address these issues in the country's highlands.. Several studies have been undertaken on soil management, which influences the physiochemical qualities of the soil and crop productivity in various ways. Thus, the primary goal of this seminar is to emphasize various literatures on the ideas of soil acidity, its causes and extents in highland areas of the country, as well as its impacts on soil and crop productivity through strategic management strategies. Many findings suggested that liming and ISFM improved soil physiochemical parameters such as soil texture, pH, accessible P, exchangeable acidity, organic carbon, exchangeable cation, cation exchange capacity, and crop yield and productivity.

I want to begin by discussing three uncertainties: the first uncertainty is about what science says and means, and how conclusive we can all be about it. This is, of course, especially the case in relation to climate change, and the frustrating thing, I suspect, for most people engaged directly in

SummaryWith the withdrawal of the UK from the European Union and increasing pressures from climate change, English arable farming resilience is in a fragile position. Most Brexit impact assessments have focused on quantitative analysis, however here we take a qualitative approach to assess how future trade agreements could impact the resilience of the UK arable farming system. We discuss the main strategies that are currently taken by English arable farmers to improve resilience using evidence from a large‐scale survey in the East of England. Using information from a multi‐stakeholder workshop, we look at arable farming resilience in three forms characteristic of the farming system; namely, robustness, adaptability and transformability and how these relate to and are potentially influenced by three different Brexit trade scenarios. Stakeholders’ recommendations suggest that a ‘hard’ no‐deal scenario will require policies for social protection of farmers in more vulnerable rural areas, while in a ‘softer’ scenario a ‘public money for public goods’ policy could be implemented effectively by learning from previous environmental schemes. Nevertheless, resilience can be enhanced only by addressing structural and policy issues, such as generational renewal, advice and extension, tenancy duration limits and smarter PPP regulations, regardless of what post‐Brexit deal with the EU finally emerges.

Soil degradation is a global threat. Developing countries are more severely affected by soil degradation than developed countries. Ethiopia, one of the developing countries in eastern Africa, is highly threatened by soil degradation problems. Soil acidity is one of the main factors that limit and prevent profitable and sustained agricultural productivity in many parts of the world . The objective of this paper is to review the extent of acid soil distributions in Ethiopia, its impact on crop production and management practices. About 40.9% of the total arable land of Ethiopia is affected by soil acidity, from these 27.7% moderately to weak acids with pH 5.8-6.7 and 13.2% covered by strong to moderate acidic soils with pH less than 5.5. According to Ethio SIS, (2014) about 43% of the Ethiopian arable land is affected by soil acidity of these about 28.1% of soils in Ethiopia are dominated by strong acid soils (pH 4.1-5.5). Most of investigators confirmed that the two fundamental factors that limit the fertility of acid soils are: nutrient deficiencies, e.g. phosphorus (P), calcium (Ca) and magnesium (Mg) and the presence of phytotoxicity substances, e.g. soluble aluminium (Al) and manganese (Mn). To overcome these problems, different acid soil management has been implemented in the country. Thus many studies have been conducted with regards to Acid soil management which influences soil physical and chemical properties and crop yield directly or indirectly. Therefore, the aim of this seminor paper is to review different literature on the extent of acid soil in Ethiopia, its impacts on some selected chemical soil properties and management methods. Different studies showed that some soil chemical properties such as pH, Ava_P, OC, CEC, Echangeable Acididy (EA), Excheanchable bases (Ca, Mg, Na and K) and crop yields were improved in different agro ecologies by effects of liming and ISFM. Soil acidity problems also can be overcome by growing crop genotypes which are adapted to acid soil condition. Thus, for sustainable agricultural systems within small-scale farming in developing countries like Ethiopia, use of integrated soil fertlity management, liming and crop varieties tolerant to Al toxicity are the mechanisms used for management of acid soils. Key note: Acidity, Lime, ISFM , Acid tolerant crop varieties DOI : 10.7176/JBAH/9-15-03 Publication date : August 31 st 2019

Acidic soils cover approximately 50 % of the arable land with high N2O emission potential. 3,4-dimethylpyrazole phosphate (DMPP) inhibits N2O emission from soils; however, its efficiency is affected by acidity. Liming is used for soil conditioning to ameliorate the effects of acidity. In the present study, we investigated the effects of liming on the efficiency of DMPP in inhibiting N2O emission in acidic soils and the mechanisms involved. We evaluated the impact of liming, DMPP, and combined application and its microbial responses in two acidic soils from Zengcheng (ZC) and Shaoguan (SG) City, Guangdong Province, China. Soils were subjected to four treatments: un-limed soil (low soil pH) + urea (LU), un-limed soil + urea + DMPP (LD), limed soil (high soil pH) + urea (HU), and limed soil + urea + DMPP (HD) for analyses of the mineral N, N2O emissions, and full-length 16S and metagenome sequencing. The results revealed that, HU significantly decreased and increased the N2O emission by 17.8 % and 235.0 % in ZC and SG, respectively, compared with LU. This was caused by a trade-off between N2O production and consumption after liming, where microbial communities and N-cycling functional genes show various compositions in different acidic soils. LD reduced N2O emission by 23.5 % in ZC, whereas decreased 1.5 % was observed in SG. Interestingly, DMPP efficiency considerably improved after liming in two acidic soils. Compared with LU, HD significantly reduced N2O emissions by 61.2 % and 48.5 % in ZC and SG, respectively. Synergy of mitigation efficiency was observed by lime and DMPP application, which was attributed to the changes in the dominant nitrifiers and the increase in N2O consumption by denitrifiers. The combined application of lime and DMPP is a high-efficiency strategy for N2O mitigation can ensure agricultural sustainability in acidic arable soils with minimal environmental damage.

Nutrient and carbon cycling along nitrogen deposition gradients in broadleaf and conifer forest stands in the east of England

Abstract. Arable crops in the UK make a large contribution to nitrate leaching by virtue of the land area they cover (>4.5 million ha). By contrast horticultural crops occupy only a small area (< 0.2 million ha) but can leach very large amounts of nitrogen. The application of nitrogen fertilizer to arable and horticultural crops is very cost‐effective, stimulating its use. MAFF's Nitrate Research Programme for arable and horticultural crops aims to reduce nitrate leaching and maintain productive farming through Best Management Practice. The Programme has led to the development and testing of methods to measure nitrate leaching, the identification of ‘leaky’ crops, soils and practices, and strategies to optimize the use of fertilizer nitrogen. Data have been used to construct and test models of nitrate leaching, which in turn have been used to evaluate the leakiness of potential rotations. Current best practice to minimize nitrate leaching requires measures to improve the efficiency of nitrogen use by crops, combined with measures to protect soil nitrogen from leaching during the late autumn to spring drainage period. This involves consideration of many factors: an appropriate crop variety must be chosen; a green cover must be maintained for as much of the year as is practicable; crops should be drilled early; fertilizer requirements should be calculated using a recommendation system and allowing for soil mineral nitrogen and any manures applied; fertilizers should be spread evenly with a properly calibrated spreader, perhaps using split applications; starter fertilizers and banding of fertilizers should be used where appropriate to reduce losses from vegetables; pest and disease infestation must be minimized; any irrigation must be applied carefully with scheduling. Research is now moving on to study whole farm systems and the interactions between losses of nitrogen and other pollutants to the environment with the aim of minimizing total environmental impact.

Acid soils represent a severe constraint for alfalfa crop in Argentina and Uruguay. The sustainable management of alfalfa pastures in these countries represents a main alternative to introduce N to the arable lands through the N-fixing symbiosis established between the plant and Sinorhizobium meliloti. Within this frame, a strategy was applied to isolate alfalfa nodulating rhizobia (ANR) from local acid soils. In a previous report we had described the isolation of an acid tolerant (AT) rhizobial population having different degree of acid tolerance. Among them, the AT isolate LPU83 was able to grow even at pH 5.0. This and other AT isolates appeared to be close relatives of the previously described bean nodulation rhizobia Rhizobium spp. Or191. Further characterization of representative acid sensitive and AT isolates was undertaken by using microcosms experiments in glass tubes that contain 30 g of a local acid soil (pH5.6, gamma irradiated) and two alfalfa plants each. All examined rhizobia presented a first week of lag phase followed by a phase of growth. In the microcosms system, no significant differences were found between the behavior of Rme LPU63, Rspp LPU83 and the acid sensitive strain Rme 2011. In all cases bacterial numbers 2 weeks after inoculation ranged between 107 to 5.109 cfu/g of soil depending on the strain and the pH of the sample. Since these strains were markedly different in their ability to grow at low pH, the presented results show that acid tolerance in culture medium can not directly be extended to predict the behavior of the strains under acid soil conditions. Thus, ANR with improved persistance in acid soils have to be searched on the basis of complementary criteria, in addition to the bacterial acid tolerance in culture medium. Currently we are investigating how our acid tolerant isolates behave in symbiosis at different pHs.

Aluminium (Al) toxicity is the main abiotic stress limiting plant productivity in acidic soils that are widely distributed among arable lands. Plant species differ in the level of Al resistance showing intraspecific and interspecific variation in many crop species. However, the origin of Al-tolerance is not well known. Three annual species, difficult to distinguish phenotypically and that were until recently misinterpreted as a single complex species under Brachypodium distachyon, have been recently separated into three distinct species: the diploids B. distachyon (2n = 10) and B. stacei (2n = 20), and B. hybridum (2n = 30), the allotetraploid derived from the two diploid species. The aims of this work were to know the origin of Al-tolerance in acidic soil conditions within these three Brachypodium species and to develop new DNA markers for species discrimination. Two multiplex SSR-PCRs allowed to genotype a group of 94 accessions for 17 pentanucleotide microsatellite (SSRs) loci. The variability for 139 inter-microsatellite (ISSRs) markers was also examined. The genetic relationships obtained using those neutral molecular markers (SSRs and ISSRs) support that all Al-tolerant allotetraploid accessions of B. hybridum have a common origin that is related with both geographic location and acidic soils. The possibility that the adaptation to acidic soils caused the isolation of the tolerant B. hybridum populations from the others is discussed. We finally describe a new, easy, DNA barcoding method based in the upstream-intron 1 region of the ALMT1 gene, a tool that is 100 % effective to distinguish among these three Brachypodium species.