Land degradation and productivity
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Analysis
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This study compares restoration of formerly cultivated prairie land versus never cultivated (native) prairie land in term of soil physical property (bulk density), chemical properties (pH, available P and N, and total stocks of C and N), microbial biomass (C and N), and mineralization of C and N (0-10cm soil depth) over 35 years. Recovery of C and N stock (which is a potential sink of GHGs) in formerly cultivated prairie land to the native level of native prairie land needs at least 350 years. Over the 35 years bulk density, available P and N decreased exponentially and soil pH increased linearly in restored prairie land compare to native prairie.
By using complex geospatial data on certain major degradation processes, i.e. aridity, soil erosion, vegetation decline, soil salinization, and soil organic carbon decline, land degradation footprint on global arable lands is assessed in this study. It showed aridity is by far the largest singular factor affecting ~40% of the arable lands' area, while soil erosion affects ~20% of global arable land. The result identified that India, the United States, China, Brazil, Argentina, Russia, and Australia are the most vulnerable countries in the world to the various pathways of arable land degradation. Also, in terms of percentages, African countries are the most heavily affected by arable degradation. This study's findings can be useful for prioritizing agricultural management practices that can mitigate the negative effects of the two degradation processes or of others that currently affect many arable systems across the globe.
A fifth of countries worldwide are at risk from ecosystem collapse as biodiversity declines. 55% of global GDP depends on high-functioning biodiversity and ecosystem services.
​Zurich (2020, p.1)​
The 13% increase in production rates for the most common crops between 2001 and 2012, due to technological improvements, more rigorous land management and an increased use of fertilizer, might have masked the ongoing degradation of soils and their ecosystem service delivery capacity.
​Borelli (2017)​
Current rates of total factor productivity growth are insufficient to prevent further land expansion, reversing in most cases the in-sample trends in land contraction observed during 2001–2010.
​Villoria (2019)​
Between 1998-2013, 20-30 per cent of Earth’s vegetated land surface showed persistent declining trends in productivity: 20% of cropland, 16% forest land, 19% grassland, and 27% rangeland.
By 2050, crop yields to fall by an average 10% globally, and up to 50% in certain regions due to land degradation and climate change. Economic cost of biodiversity and ecosystem services loss from land degradation is over 10% of annual global gross product. Between 2000 and 2009, annual emissions from land degradation were 3.6–4.4 billion tonnes of CO2-e. by 2050, losses of 36 Gt of carbon from soils projected – mostly in Sub-Saharan Africa.
​IPBES (2018)​
Over 1/3 of the terrestrial land surface being used for cropping or animal husbandry (agriculture).
Land degradation has reduced productivity in 23% of global terrestrial area.
​IPBES (2019)​
Production yields of Australian cereal grain remained relatively unchanged for decades. This can be explained by the rapid ageing and degradation of the cropping land due to a period of halted expansion.
This perspective has important implications for future scenarios of the Australian cropping industry, which are unlikely to maintain land expansion [ie land clearing] at the long-term average of about 2% pa.
Without major change, land degradation in our model results in yield loss of nearly 30% by 2060.
Soil carbon loss by wind erosion is very significant in agricultural drylands and is not being properly counted. SOC erosion by wind occurs to a large magnitude in every global region of the vast Earth’s drylands (45% of the land surface). The substantial amount of SOC change is negative. Omission of SOC erosion from the LDN framework as a key process would likely cause inaccurate assessments of resource condition and highly uncertain policy advice.
We map net (1950s–1990) SOC redistribution across Australia and estimate erosion by all processes to be ∼ 4 Tg SOC yrβˆ’1, which represents a loss of ∼ 2 % of the total carbon stock (0–10 cm) of Australia. Assuming this net SOC loss is mineralised, the flux (∼ 15 Tg CO2-equivalents yrβˆ’1) represents an omitted 12 % of CO2-equivalent emissions from all carbon pools in Australia. Although a small source of uncertainty in the Australian carbon budget, the mass flux interacts with energy and water fluxes, and its omission from land surface models likely creates more uncertainty than has been previously recognised.
Annual SOC dust emission for Australia are 5.83 Tg CO2-e yr1 and 0.4 Tg CO2-e yr1 for agriculture soils. These amount to underestimates for CO2 emissions of 10% from combined C pools in Australia (year = 2000), 5% from Australian Rangelands and 3% of Australian Agricultural Soils by Kyoto Accounting.
55% of Australia is experiencing a loss rate of 0.5 tonnes per hectare per annum [23]. 16% of Aust particularly in agricultural zones, are at a considerable risk (e.g., 70% chance) of being higher than 0.5 tonnes pa [25].
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The success in reducing soil erosion through such a widespread practice change [eg no-till and conservation tillage] has led to a belief in some quarters that soil erosion is no longer a major problem for farmers. As a result, State Government programs to address soil erosion have been scaled back over recent decades [21]. This has led to a level of confidence that soil erosion has been addressed, but erosion levels are still above tolerable and regenerative limits and will continue to impact agriculture, particularly under a changing climate, unless preventing further soil erosion remains a focus.
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Soil acidification is estimated to affect over 50 percent of cropping and/or intensively grazed regions, with soil acidity in many agricultural regions continuing to deteriorate [16]. Soil acidity in WA is impacting state farm gate returns to the tune of $400 million per annum through lost production. This region produces half of Australia’s wheat (Triticum aestivum L.) crop and supplies 80 percent of the wheat exports [19].
Australian agricultural soil has lost between 40 and 60 percent of its soil carbon content since settlement [20].
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Water erosion is now outstripping soil formation rates across Australia by a factor of several hundred and in some areas, several thousand [16]. The average erosion rate to be 4.1 ton/ha/year across the continent, and that about 2.9 Γ— 109 tonnes of soil is moved annually, representing 3.9 per cent of global soil erosion from 5 per cent of world land area [22].
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The strongest determinant of wind erosion may be climate [16]. Climate change in Australia is expected to result in more extreme wind and flooding events. Both have been experienced across the continent during the past decade and anecdotally caused significant dust storms and soil loss through water erosion [16].
​Koch et al. (2015)​
Significant thresholds will be crossed in 2050, tipping Australia into runaway land degradation, unless changes are made to production methods to reverse this trend, such as agro-ecological practices.
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