I read more and more stuff about alternative method of agriculture such as permaculture. Howerver, I'm not an ecologist or biologist so I don't know where to look for really good and serious articles / paper on the subject. I am really interested in food production methods that may be efficient and respectful for both the environment and the health.
The question that interests me the most is the question of crop yield and environment. I wonder if there are studies that compares the crop yield of the different production methods AND if there are scientific researches on the optimisation of the food production under ressources constrains.
Do you have any reading suggestion? I'm mostly interested in scientific papers but I'm open to anything that may be interesting.
I believe you are looking for information on "sustainable agriculture". There are many aspects of production in agriculture like: fertilization, irrigation, pesticides and (no-)tillage. One can try to calculate the carbon foot-print of food (beware of the calculations, they might be misleading).
Crop rotation is helpful in sustainable agriculture but it is not always available, making traditional (industrialized) agriculture the only viable option. The economic aspect is also important. Agricultures need to grow the food and they will grow it only if the make money from it. Organic and sustainable agricultural products get a premium for being cultivated that way but these premia go down as more farmers use them.
The question "How the yield is affected by the agricultural method" is a broad question that attract interest in research. We need to break it down to: What is yield (biomass? marketable product?) and what is agricultural method.
A great study conducted in Ontario, Canada by Stonehouse et al, 1996 compares the herbicide treatments in 3 types of farms: conventional, reduced input and organic and the yield, investment and profit for three crops: grain corn, beans and cereal grains. The data arrives from self-reported data by the farms. This is not a fully randomized experiment and there are many differences between farms (size, investment, land) but precautions were taken to reduce them. Reduce input farmers used less herbicides than the conventional ones.
This is the table from the article There reported more information as profitability but since this study is from 25 years ago I believe it is no longer relevant.
This study is only one showing the complexity of the subject and one of the methodologies employed. One can write various books about the subject so I hope this post gives you the direction that you needed
Publications by the Food and Agriculture Organization http://www.fao.org/documents/card/en/c/ca9692en of the United Nations would be a good place to start as they are freely accessible. There are plenty of articles looking at crop yield of different production methods and different management techniques. You may consider subscribing to a journal, like Agronomy https://www.agronomy-journal.org/, or CAB Abstracts https://www.cabi.org/publishing-products/cab-abstracts/ as those would contain most of the subject material you're looking for. Those would also contain information on optimizing food production under resource constraints. Happy researching!
Maximum Sustainable Yield
21.2 Aquaculture, food safety and HACCP systems
According to statistics, wild capture fisheries are at the maximum sustainable yield and future increases are unlikely. Wild captured commercial fisheries cannot continue to meet the increasing worldwide demand for high quality/safe fishery products ( FAO, 2004 Martin, 2002 ). Aquaculture will, on the other hand, help to meet the world's future protein requirements ( Martin, 2002 ). Aquaculture production with an annual growth rate of 8.8% since 1970 is the fastest growing food supply sector ( Fig. 21.1 ). Although recent indications indicate a leveling off of production ( FAO, 2006 ), the Food and Agriculture Organization (FAO) estimates that one in three fish eaten is aquaculture produced with approximately 90% of all aquaculture fishery products being produced in Asia ( FAO, 2004 ). In 2004, 59.9 million tonnes of aquacultured fishery products including aquatic plants were aquacultured with a value of US$70.3 billion ( FAO, 2006 ).
Fig. 21.1 . Trend of world aquaculture production by major species groups ( FAO, 2006 ).
China is leading the world in aquaculture production representing 69.6% of the total quantity produced and over half of the global value ( Fig. 21.2 ) ( FAO, 2006 ). Much of the production in China and in developing countries is for domestic consumption, but increasing amounts are being raised for export to the USA, Europe and Japan.
Fig. 21.2 . Aquaculture production: major producer countries 2004 ( FAO, 2006 ).
The value of international trade in fishery products increased from US$15.4 billion in 1980 to US$71.5 billion in 2004 ( FAO, 2006 ). In eight out of eleven countries that were studied, international trade had a positive impact on food security in these countries ( FAO, 2006 ). The international trading of seafood products is a complex issue, and expectations by countries and their citizens are that fishery products are safe and are high quality. In that regard, more and more countries and regional customs organizations are taking steps to control food safety hazards to an acceptable level of protection ( Garrett, 2002 ). Numerous countries have implemented food control management systems such as Hazard Analysis Critical Control Point (HACCP) to ensure food safety ( Garrett, 2002 ). Hazard Analysis Critical Control Point is a science-based food safety management system developed by the Pillsbury Food Company USA in the late 1960s to ensure the safety of food for astronauts during the USA NASA Apollo Moon Program. Since that time, it has been accepted by countries around the world as a science-based risk management tool to help ensure food safety from production to consumption ( Lima dos Santos, 2002 ). Recently its use has been expanded to include control of potential human, animal and environmental hazards associated with aquaculture ( Jahncke and Schwarz, 2002 Lima dos Santos, 2002 ).
Countries around the world are detaining and rejecting fishery products that are contaminated with pathogens such as Salmonella spp., or contain chemicals such as antibiotic residues ( Anonymous, 2005b , 2006 , 2007 Garrett et al., 1997 , 2000 ). Several exporting countries of fishery products have had their fishery products placed on detention without physical examination (DWPE) by the USA and other countries based on past history of problems with pathogens and chemical contamination. In response, countries such as Vietnam, Thailand, China and others, are implementing strict testing protocols of their fishery products to help ensure their ability to export their products to countries such as USA, Japan, Europe, Russia, etc. ( Anonymous, 2005b , 2006 , 2007 ).
A survey conducted by the United States Food and Drug Administration (USFDA) in 1998, showed that 6.4% of the imported aquacultured seafood was found to contain Salmonella, while less than 1% of wild captured fishery products were contaminated with Salmonella ( Koonse, 2008 ). Between 2000 and 2003, the USFDA analyzed 1744 samples of imported raw shrimp, primarily from aquaculture operations. Approximately 10% of these samples were positive for Salmonella and were detained ( Koonse, 2008 ). Antibiotic residues found in many aquacultured fishery products are also a major reason for detention and rejection by importing countries ( Anonymous, 2005a ). Disease outbreaks in aquaculture operations are a common occurrence. Unfortunately, many aquaculture farmers turn to the indiscriminate and inappropriate use of antibiotics to address disease issues at their aquaculture farms. For example, the use of antibiotics to treat shrimp viral diseases is not appropriate, since viruses cannot be successfully treated with antibiotics. In addition, most countries have regulations concerning approved use of specific antibiotics, appropriate use levels, withdrawal times that can be used under the supervision of a veterinarian or equivalent professional, to treat specific diseases and specific species ( FDA, 2005 JSA, 1997 , 2004 ). Exporting countries must know and understand the regulatory requirements of the importing countries concerning the proper and accepted use of chemicals and chemotherapeutics to treated aquacultured species, or their products will be detained and rejected by the importing country. The key to reducing use of antibiotics in aquaculture is to integrate proper use of drug applications with Good Aquaculture Practices (GAqPs) ( Jensen and Greenless, 1997 ). Application of HACCP principles can also be used to control pathogens and chemicals in aquacultured products ( JIFSAN, 2007 Jahncke and Schwarz, 2002 ).
The FAO has been instrumental in providing training programs on the use of HACCP principles in aquaculture in countries around the world. Several aquaculture farms in Brazil, with encouragement from the government, introduced HACCP principles to control chemical contaminants, food additives, veterinary drugs, pesticides, heavy metals, and pathogenic bacteria ( Lima dos Santos, 2002 ). The government in Chile developed guidelines on the Control of Veterinary Drug Residues in Aquacultured Products ( SERNAPESCA, 2000 ). Several countries in South East Asia are applying HACCP Principles and Best Management Practices (BMPs) to control drug and chemical use and to protect the environment ( Suwanrangsi, 1997 Tookwinas and Suwanrangsi, 1997 Lima dos Santos, 2002 Koonse, 2006). It has also been used by the FAO in Laos, Vietnam and Cambodia to successfully control infestations of freshwater aquacultured carp (Puntius goniotus) fish by the parasite Opisthorchis viverrini ( Khamboonruang et al., 1997 Lima dos Santos, 1994 ).
The seven principles of HACCP have also been applied for shrimp aquaculture operations to control pathogenic shrimp viruses such as Taura syndrome virus (TSV) (Picornaviridae), yellow head virus disease (YHV) (Baculorviridae), and white spot syndrome baculovirus complex (WSSV) ( Jahncke et al., 2002 ). The USFDA Joint Institute of Food Safety and Applied Nutrition (JIFSAN) recently developed a Good Aquaculture Practices (GAqPs) Train-the-Trainer course to help reduce the use of chemicals and antibiotics in aquaculture. The use of HACCP principles as a risk management tool to control the use of antibiotics in aquaculture was identified in the training workshop as an effective method to control chemotherapeutic use in aquaculture ( JIFSAN, 2007 ). Training is also being offered by the Pennsylvania Sea Grant and the US Fish and Wildlife Service USA on the use of the general principles of HACCP to control the spread of invasive aquatic species into the environment ( Faulds, 2007 ).
Sustainable agriculture: Guaranteeing yield while reducing greenhouse gases
Mario Corrochano-Monsalve. Credit: UPV/EHU
The NUMAPS group of the UPV/EHU has analyzed the benefits of adding nitrification inhibitors to ammonium-based fertilizers. The study was conducted on a wheat crop and compared a conventional tillage management system with one involving minimum tillage. To do this, parameters such as grain yield and quality, efficiency in nitrogen use and greenhouse gas emissions, among other things, were measured.
Crop growth is limited by the nitrogen availability in the soil, one of the primary elements of plants, the deficiency of which leads to a fall in agricultural yield. So nitrogen needs to be added to the soil in the form of nitrogen fertilizers. Yet this applied nitrogen may not be efficiently used by the crop. This fact not only leads to significant economic losses for the farming sector, it causes environmental problems, such as water eutrophication due to nitrate leaching, ammonia volatilization, and production of nitrogen oxide (nitric oxide and nitrous oxide) produced by the microorganisms in the soil. The emission of nitrous oxide (N2O) is hugely significant, as it is a greenhouse gas with a global warming potential 265 times higher than that of CO2.
In order to mitigate these nitrogen losses in agriculture, "agronomic research has to focus on optimizing the use of nitrogen fertilizers by developing better farming practices that will not only help to prevent leaching and gaseous losses, but also to obtain maximum crop yield and quality," says Ph.D. student Mario Corrochano-Monsalve, one of the researchers in the NUMAPS (NUtrition MAnagement in Plant and Soil) group of the UPV/EHU.
In this respect, the researchers have conducted a study focusing on the use of nitrification inhibitors. Inhibitors of this type slow down the activity of certain bacteria that inhabit agricultural soils and which use the ammoniacal nitrogen provided by the fertilizers for their own growth, thus competing with the plant crop for it. "The use of inhibitors enables the plant to have more time to absorb nitrogen from the soil and assimilate it in the form of amino acids and proteins, thus reducing its loss in the form of nitrates or nitrogen gases," explained the researcher.
Toward efficient agriculture
The group conducted a field experiment "to see the effect of using an ammoniacal fertilizer combined with a type of nitrification inhibitor (3,4-dimethylpyrazole-succinic acid DMPSA) on two crop management systems: conventional tillage (deep furrows with moldboard) and minimum tillage (minimum plowing, the seeds being sown in small holes)," according to Corrochano-Monsalve.
The plots were exhaustively monitored. Corrochano-Monsalve says, "On each plot, we measured the wheat yield, its quality as bread flour, the evolution in soil nitrogen content and greenhouse gas emissions (GHG) (CO2, N2O and CH4) of the cultivated soil the genetic indicators of the variation of bacteria populations in the soil responsible for nitrogen oxidation/reduction and therefore its emission as GHG were also analyzed."
The main conclusion of the study is that "the use of the nitrification inhibitor in combination with minimum tillage improved crop efficiency, and reduced the GHG emission without affecting yield," explains Corrochano-Monsalve. "The most novel aspect of the work is the confirmation that the use of nitrification inhibitors on crops with a minimum tillage system encourages the growth of certain bacteria populations that reduce the N2O to molecular nitrogen (N2), the most abundant form and which does not react with the nitrogen in the atmosphere. That way, the loss of nitrogen in the form of gas would be harmless."
In humid Mediterranean climate conditions, like that of Álava, where the study was conducted, "in many phases of the crop cycle, we find high levels of soil humidity that may increase nitrogen losses through leaching. Yet the high degree of humidity also generates a highly anaerobic environment that encourages the reduction of N oxides to N2," he says. "The use of nitrification inhibitors can be expected to enable a smaller amount of fertilizer to be applied, which, besides a reducing the environmental impact, would lead to economic savings for farmers.
"Agriculture, just like many other sectors, has to be more and more efficient. It is about achieving sustainable agriculture that combines food security (food for everyone) with the minimum environmental impact," he concludes. Until now, general recommendations have been made for each geographical area (amount of fertilizer, chemical formulation, when and how to apply it, type of plant protection products, etc.). However, the ideal thing, and which is a growing trend, is to customize the recommendations much more. In other words, even each plot within a single geographical area has its unique features, and the ideal thing would be before the start of a growing season for each plot to be analyzed beforehand to determine exactly what its needs are and thus prevent the wasting of resources."
Adaptation of nitrate reductase activity assay for high throughput screening of crops
- G I. Karlov
- , D. Y. Litvinov
- , P. N. Kharchenko
- , P. Yu. Krupin
- , S. Yu. Shirnin
- , A. .G Chernook
- , L. А. Nazarova
- & M. G. Divashuk
Siberian Herald of Agricultural Science (2020)
Marandu Palisadegrass Mineral Nutrition and Production Related to Nitrogen and Potassium Supply
Journal of Plant Nutrition (2015)
Biomass Industrial Effluent Effect on Carbohydrates, Aminoacids, Nitrite and Nitrite Enzyme Activities of Arachis hypogaea L.
- PC Nagajyoti
- , N Dinakar
- , S Suresh
- , Y Udaykiran
- , C Suresh
- , TNVKV Prasad
- & T Damodharam
Agricultural Sciences in China (2009)
Impact of genotype and micronutrient applications on nitrate reductase activity of tea leaves
Journal of the Science of Food and Agriculture (2005)
Factors affecting nitrate reductase activity in some monocot and dicot species
Journal of Plant Biology (2003)
DEPENDENCE ON FERTILIZERS
Grain yield is dependent on many factors – soil, irrigation, genetics, climate, cultural practices, pests and disease control and fertilizer application. Crops developed during the Green Revolution are high-yield varieties – domesticated plants bred specifically to respond to fertilizers to produce an increased amount of grain per acre planted. In fact, these high-yield varieties cannot grow successfully without the help of fertilizers.
In fact, research shows that fertilizers can account for 30% to 70% of the yield. This very significant contribution explains why many farmers believe that if they apply more fertilizers, they will obtain higher yields. However, there is a limit to fertilizer effectiveness.
The relation between fertilizer application rates and potential yield is schematically described in the following diagram:
Based on abundant field trials and consequent data analysis, the curve demonstrates the yield response to fertilizer application. We can learn a few things from looking at the graph.
When no fertilizer is applied, yield reaches some minimal level of potential. Then, yield increases along with an increase in the fertilizer application rate.
Eventually, yield reaches its maximum level of potential. Notably, we see that a plant can’t accept more nutrients than it needs, after which addition of fertilizer does not increase the yield.
In fact, when fertilizer application rates become too high, plants suffer from salinity damage and specific nutrient toxicity, resulting in decreasing yield.
Moreover, we have found that since local conditions may vary significantly between fields, a fertilizer-yield curve that was established for one field will not be valid for another, even on the same farm.
In addition, the very same crop might require different fertilizer application rates at different times during the year and in different locales. For example, the potential maximum yield for wheat on this farm might change from year to year due to weather fluctuations.
In other words, trying to apply a general fertilizer recommendation across the board is not much better than a wild guess.
To obtain optimal results, you must plan a fertilizer program that is specific to your field in a certain season. Since every field has its own nutrient composition, the accurate approach would be to use soil, plant and water analysis, and to adapt the fertilizer program according to specific conditions.
The yield response curve we presented above shows how fertilizer application rates affect crop yield. But, in fact, it is not only the total fertilizer application rate that is at play here it is also the application rate of each individual nutrient.
According to Leibig’s Law of the Minimum, crop yield is determined by the most limiting factor in the field. This implies that if but one nutrient is deficient, yield will be sub-optimal, even if all other nutrients are available in sufficient quantities.
Extent of climate-driven agricultural frontiers
Climate-driven agricultural frontiers as defined here cover between 10.3–24.1 million km 2 of the planet’s surface, with an ensemble median value of 15.1 million km 2 under RCP 8.5 by 2060–2080 (Fig 1, S2 Fig). Crops that comprise the frontiers are shown in supplementary S3 and S4 Figs and are primarily more cold tolerant temperate crops such as potatoes, wheat, maize, soy. To put the magnitude of these agricultural frontiers in perspective, the ensemble median area of agricultural frontiers under this late century, RCP 8.5 scenario is equivalent to 59% of current global cultivated and managed vegetation land area, while the ensemble maximum area is equivalent to 93% of current cultivation. Under a RCP 4.5 scenario, with more muted radiative forcing, agricultural frontiers are found to cover 8.1–20.0 million km2 of the earth’s surface (equivalent to 31–77% of currently cultivated area (see S2 Fig)). Soil quality, terrain and infrastructure, however, will be major determinants of which of these frontiers will actually be cultivated and as such, the results presented here represent an upper bound estimate of where cropland expansion may be expected.
Areas that transition from no current suitability for major commodity crops to suitability for one or more crops are depicted in blue, while currently uncultivated areas that transition to suitability for multiple major commodity crops are shown in red. Intensity of color indicates the level of agreement between simulations driven by different GCMs for the RCP 8.5 radiative concentration pathway. Terrestrial areas in white are either currently suitable for at least one modeled crop or, not suitable for any modeled crops in the projected climatic conditions. Suitability under current and projected climates is defined as universal agreement of suitability methods (EcoCrop, Maxent, Frequency of Extreme Temperatures).
Geographic distribution of climate-driven agricultural frontiers
Frontiers are projected to be most extensive in the boreal regions of the Northern Hemisphere and in mountainous areas worldwide, since areas suitable for commodity production generally expand upslope and towards the poles in response to rising temperatures. Potatoes, wheat and maize make the largest contributions to frontier land surface (S4 Fig). Canada (4.2 million km 2 ) and Russia (4.3 million km 2 ) harbor the greatest area of agricultural frontier (RCP 8.5, ensemble median). Among montane regions, the Mountains of Central Asia and the Rocky Mountains of USA and Canada have the greatest frontier area (0.1 and 0.9 million km 2 , respectively). Frontiers on the fringes of Australian and African deserts are the result of projected increases in precipitation, for which there is relatively low GCM agreement, including divergent trends in sign of precipitation change among GCMs. This makes conclusions about potential for agricultural expansion in these areas highly uncertain. In contrast, there will be a small loss of existing crop area. We estimated that about 0.2% of existing crop area will become unsuitable for all modelled crops without irrigation or other intensive inputs for RCP 8.5 2060–2080 scenario.
Environmental impacts of climate-driven agricultural frontiers
Environmental impacts from climate-related agricultural land use change include impacts on climate services (e.g., reduction in carbon storage), the effects of agricultural pollution on downstream areas, and degradation of natural habitats with attendant loss of biodiversity [47–52]. The most significant impact is likely reduction in climate services provided by carbon storage in frontiers soils, particularly in the extensive high latitude frontiers.
Climate services impact
The total amount of carbon that resides in the top 1 m of soil under agricultural frontiers has a median value of 632 GtC (gigatons of carbon) (RCP 8.5, ensemble) and 539 GtC (RCP 4.5, ensemble), with a minimum RCP 8.5 ensemble value of 400 and a maximum value of 991 GtC (Table 2). This is equivalent to 47–116% of all carbon currently in the Earth’s atmosphere (Fig 2). Release of carbon from high latitude soils due to warming is already of major concern but may be small relative to the amounts of carbon that might be released if these areas come under cultivation .
Areas with >50% GCM agreement commodity frontiers are shown. Existing agricultural land cover >10% of each pixel is represented in light brown.
Rows with grey shading apply GAEZ general soil suitability constraints and soil requirements for each crop to the climatically suitable frontier areas.
The release of carbon following tilling from previously untilled soils is believed to occur rapidly and estimates suggest that 25–40% of total soil carbon is released within five years of plowing . Therefore, an upper bound estimate of the total amount of carbon that might be released from the cultivation of climate-driven frontiers would be on the order of 177 GtC, which is equivalent to 119 years of current CO2 emissions of the United States . The actual area affected would be smaller than the frontier due to economic and physical factors, but emissions might be greater because many of the potentially affected soils are peat, which may degrade when disturbed, releasing more and deeper carbon. In either event, the magnitude of the potential release indicates that policies directed at constraining development of these areas are vitally important. From a global perspective, 177 GtC is more than two-thirds of the 263 GtC within which total future emissions must be constrained to limit global mean temperature increase to the internationally agreed Paris agreement target of 2°C global mean temperature increase above pre-industrial levels .
One way to address the challenge posed by cultivation of frontiers is through promoting agricultural management practices that conserve soil-bound carbon. In particular, policies that incentivize leaving peat soils intact and promoting conservation tillage could significantly reduce the quantity of carbon released and slow the speed at which it is released [57–58]. Thus, while specific estimates as to the speed or extent to which these carbon sources might affect the atmosphere is beyond the scope of this study, it is highly likely that developing such regions for agriculture will have significant impacts on greenhouse gas emissions that need to be balanced against the benefits of increased food supply and constrained by sound environmental policies.
The biodiversity impacts of the climate-driven frontiers occur where the frontiers intersect with important ecosystems and habitats (Table 3). Among global priorities for biodiversity conservation, 56% of global biodiversity hotspots, 22% of Endemic Bird Areas (EBAs) and 13% of Key Biodiversity Areas (KBAs) intersect with climate-driven agricultural frontiers (ensemble median RCP8.5 2060–2080 see Table 3). Biodiversity hotspots that have the largest intersection with frontiers are the Tropical Andes, the Mountains of Central Asia, the Horn of Africa and the Chilean Winter Rainfall and Valdivian Forests.
Areas of significant biodiversity resources assessed are biodiversity hotspots endemic bird areas (EBA) key biodiversity areas (KBA). Numbers presented for biodiversity resources are the median [range] number of areas that intersection with frontiers across all GCMs. Potential impacts on restricted range bird species are presented as the median [range] number of species with modeled range intersection with frontiers in current and 2060–80 climate projection. Modeled future ranges are assessed under an assumption of no-dispersal and a 10 km/decade dispersal rate.
Species’ ranges may move in response to climate change, causing changes in patterns of biodiversity, at the same time as frontiers are opening. To test the effect of frontiers on future, as well as present, patterns of biodiversity, the ranges of all global restricted range birds, a set of high conservation priority species found in hotspots, KBAs and EBAs, were modelled . These results show that the number of restricted range birds impacted by frontiers increases in the future from 409 species to 491 species under RCP8.5 representing 20% of the 2,451 global restricted range bird species and 409 to 362 under RCP4.5 (Table 3). Thus, range shifts due to climate change accentuate the intersection of frontiers with suitable climate for rare species, as both crop suitability and suitable climate for species move upslope. However, this effect depends on species’ ability to occupy newly suitable areas. Species potentially impacted by frontiers are most numerous in Central America and the Northern Andes, with secondary concentrations in the Himalayas and highlands of New Guinea.
Water quality impacts
The potential impact of climate-driven agricultural frontiers on downstream water quality has may affect large numbers of people and their water infrastructure. The agricultural water quality (AWQ) footprint of frontiers encompasses the homes of between 0.4–1.0 billion people (RCP 4.5, ensemble minimum and maximum) and 1.2–1.8 billion people (RCP 8.5, ensemble minimum and maximum), of whom 900 million-1.6 billion (RCP 8.5, ensemble minimum and maximum) live in areas in which more than half of the water supply is projected to be impacted (Table 4). Water quality changes in these downstream areas from fertilizer and biocide runoff may affect human health, ecosystem health, production of fisheries and the cost of water treatment.
Elevated AWQ is >50% of water supply with AWQ impacts.
Table 4 shows that agricultural frontiers increase the amount of land potentially affected by changes in AWQ 9% to 16% (median 12%) compared to current impact (RCP 8.5, ensemble minimum and maximum). Given that some of this new farmland (in drylands) will not generate significant runoff, under RCP 8.5 the land area with AWQ varies from a maximum additional 7–12% (median 9%) with the maximum additional global population affected varying from 9–10% (median 9%). Elevated levels of AWQ (>50%), affecting 3–6% of additional land surface (median 4%), impacting an additional 2–3% (median 2%) of the current global population. The additional AWQ per unit land area of new cropland varies between ensemble members and reflects the distribution of cropland in runoff generating areas vs not, as well as the downstream differential mixing of runoff from agricultural and non-agricultural land under different spatial frontier outcomes.
Hydrologic infrastructure, including the global estate of reservoirs created by dams that are essential for urban water supply, irrigation and hydropower are also potentially affected by the AWQ footprint of agricultural frontiers. 6.4–8% (median 7.3%, RCP8.5) or 5.5–6.9% (median 6.3% RCP4.5) of global reservoirs would experience increased AWQ impacts as a result of agricultural frontiers and 2.0–3.8% (median 2.9%, RCP 8.5) or 1.7–3.1% (median 2.4% RCP4.5) of reservoirs would be exposed to elevated impacts (AWQ >50%). These are in addition to the 63.3% of reservoirs already with AWQ>0 under the current distribution of crop suitability (50.2% at >50% AWQ) (Table 4).
To account for the uncertainty of future climate projections, all impacts of climate driven agricultural frontiers were assessed on an individual GCM/RCP/time period basis and results are presented as ensembles across all climate projections. The choice of binary threshold is a possible source of uncertainty, but in this analysis that uncertainty is constrained by choosing a threshold that is conservative from the perspective of frontiers. For instance, in EcoCrop a threshold of 20 (“very marginal to marginal”) includes areas that are possible but not optimal for cultivation [22–23]. The total area of frontiers is largely insensitive to adjustments to the choice of threshold across all methods used, because under a more permissive threshold the currently suitable area will expand, but there will be an accompanying expansion of frontiers poleward—and vice versa for a less permissive threshold. Uncertainty is more difficult to constrain in precipitation-driven frontiers where there is high disagreement on sign of change in GCMs. This makes Sahelian and Australian precipitation-driven frontiers much more uncertain than other frontiers, as noted above. The greatest uncertainty is in actual cultivation of frontiers, as discussed below. Comparison of the modeled crop distributions for both current and future climates including the possible reduction of frontier areas due to soil constraints as defined by the union of GAEZ soil resource classifications are shown in S5–S8 Figs.
Advantages of Soilless Agriculture
- Soilless agriculture does not require the use of toxic chemicals. Unlike soil-based agriculture, where farmers have to use fertilizers to increase crop yield and spray pesticides to keep weeds and pests away, crops are somewhat protected from pests and weeds.
- Soilless agriculture is ideal in urban areas where space is too limited for soil-based gardens.
- Nutrient and growing media loss is significantly reduced with soilless cultivation because the nutrient requirements for crops are determined in advance.
- Soilless cultivation is believed to cause less pollution.
- Compared to soil cultivation, the yields from soilless cultivation are significantly higher as a result of intensive practices and the possibilities of continuous, year-round production.
Optimal agriculture: maximum yield with minimum environmental impact - Biology
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Materials and Methods
Data used for this study is obtained from the Global Agro-ecological Zones (GAEZv3.0), the detailed methodology of which is presented in the GAEZv3.0 model documentation . In short, based on principles of land evaluation, GAEZv3.0 estimates crop production potential described as the agronomically possible upper limit of crop yields for individual crops under given agro-climatic, soil, and terrain conditions for a specific level of agricultural inputs and management conditions. For crop production potential, GAEZv3.0 defines three generic input levels (low, intermediate, and high input levels). Under a low-input level, the farming system is considered largely subsistence and labor intensive based on traditional management, using local crop varieties. Under an intermediate-input level, the farming system is considered partly market oriented with a mixture of subsistence based and commercial scale production. Under a high-input level, the farming system is assumed to be mainly commercial agriculture with mechanized management, using adequate nutrients, agro-chemicals, and high yielding crop varieties. Additionally, to supplement potential yield information, GAEZv3.0 also provides downscaled crop yields and area harvested for the year 2000.
Production Gaps and Calorie Deficits
We defined crop production gaps as a ratio between the potential and the current crop calorie production. To estimate the calorie productions, we used data on current and potential crop yields, and area harvested in 2000 for 19 crop types from GAEZv3.0  and nutritive factors for converting crop mass into calories from FAO  (S1 Table). GAEZv3.0 provides in a global raster grid of 5 arc minutes resolution information on both current and potential crop yields for two types of water supply (irrigated and rain-fed), and potential crop yields for the three input levels. We estimated the potential crop calorie production using crop yield data under high-input levels (S1 Text).
We analyzed crop calorie deficits based on the demand and supply of crop calories. The demand side consists of human vegetal product consumption and crop-based feed provided to livestock, which were calculated from gridded feed data , countrywide per capita vegetal product intake , and gridded population data  for the year 2000. The supply side includes crop calorie production that was derived from GAEZv3.0  (S1 Text). Since agricultural production constraints and management vary with agro-climatic conditions, crop calorie deficits and production gap analysis was conducted in sub-national moisture regime units . The seven moisture regime categories used here are: hyper-arid, arid, dry semi-arid, moist semi-arid, sub-humid, humid, and per-humid. We identified regions with crop calorie deficits considering the current and the potential crop calorie production (S1 Text). Afterwards, we classified these regions into six groups based on prevalence and depth of crop production gaps and crop calorie deficits (S1 Text). By doing so, we located regions where closing production gaps results in FSS or significantly reduces calorie deficit status in a single global map.
Scenario analysis for two scenarios (scenario A and B) were used to identify regions where closing the production gaps matters and ensures future FSS by 2050 applying the above described method. Scenario A in which population changes but dietary patterns remain constant at in the year 2000 level, is a baseline scenario. Scenario B accounts for country specific changes in dietary patterns in addition to the population growth maintaining a minimum calorie intake of 2,535 kcal/cap/day, representing the average for high calorie diets . In this way, we accounted for changes in population  and dietary patterns  that drive future food and feed demand [1, 2, 28], and progress on closing crop yield gaps that influence future food and feed supply [10, 12] (S1 Text).
Yield Gap Factors
We observed substantially larger yield gaps for rain-fed farming than for irrigated farming (S1 Fig). Globally, rain-fed farming covers 74% of cultivated land. So far it produces only 44% of the potential calorie production while irrigated farming has attained 60% of the potential calorie production. Hence, we focus this analysis on rain-fed cultivated land as it has a larger potential of additional crop production by closing yield gaps than irrigated land.
A number of biophysical and socioeconomic factors puts constraints on crop yields [32, 33], resulting in yield gaps that can be tackled with adequate agricultural input and management (Fig 1). Initially, we analyzed the biophysical factors that can be overcome by shifting farming practices from traditional low-input to high-input advanced management. We started the analysis looking at agro-climatic constraints related to yield losses due to pests, diseases, weeds, and workability. The first three of the constraints can be reduced by improved pest management. However, the workability constraint related to weather conditions affecting the efficiency of farming operation (e.g., excessive wetness causing problems in harvesting and handling of crop products) is hard to tackle.
The light green boxes represent the input data obtained from GAEZv3.0 . The applied procedures are symbolized by the light orange diamonds, which are explained in S2 Text. The light red box shows the obtained result.
We obtained data on crop specific agro-climatic constraints for low and high input levels at a 5′ resolution from GAEZv3.0. The constraints are characterized through the attainable percentage of the crop yields. Crop yields are determined by radiation and temperature regimes and water availability for a specific input level. The attainable percentage of crop yields is higher for high-input level, closing crop yield gaps, compare to that for low-input level. This is because improved pest management can reduce agro-climatic constraints related to yield losses due to pests, diseases, and weeds. We estimated the difference between the agro-climatic constraints for low and high input levels. The differences were calculated for crops in the two major crop groups (cereals and roots-tubers) and averaged with weights based on harvested area. In the year 2000, these two crop groups combined contributed around 80% of the total crop calorie production. By this, we identified regions where agro-climatic constraints could be attenuated by shifting from low to high input farming based on the weighted difference between agro-climatic constraints larger than 5% (Fig 1 and S2 Text).
As the second factor, we identified regions where crop production is hampered by soil quality constraints. GAEZv3.0 differentiates seven soil qualities and classifies them into four spatially explicit categories: no or slight, moderate, severe, and very severe constraints. Among them, constraints related to three soil qualities (rooting conditions, excess salt, and toxicity) are difficult to overcome using high inputs. Moreover, nutrient availability is an essential soil quality to attain high yields and is assessed separately as described in the next section. Hence, we identified regions where constraints related to one or more of the remaining three soil qualities (nutrient retention capacity, soil drainage, and soil workability) are moderate to very severe. These are the regions where crop yields can be increased by soil and land management that improves the soil qualities.
Next, we attempted to capture socioeconomic factors playing important roles in closing yield gaps based on two indicators: yield variability and travel time to the nearest market. The yield variability due to weather conditions may make farmers reluctant to take risks in terms of input applications without which crop yield increments are difficult . GAEZv3.0 provides data on the coefficient of variation of agro-climatically attainable yields for the baseline period of 1961–1990 . We used this data for crops in two crop groups (cereals and roots-tubers) to estimate the weighted yield variations based on irrigated and rain-fed harvested area, and identified regions with overall year-to-year yield variations larger than 20% (S2 Text).
Travel time to the nearest market is an important factor in enhancing agricultural productivity as it determines farmers’ accessibility to inputs and influences market approachability for selling agricultural products. Consequently, we used spatially explicit accessibility data presenting travel time to the nearest market with a population of around 50,000  to identify regions with a connecting time longer than 6 hours to markets. We used the traveling time of 6 hours as threshold because the numbers of smaller cities and towns decreases subsequently with increase in the travel time beyond 6 hours .
We integrated the information from the four constraints (agro-climate constraints, soil quantity constraints, weather induced yield variability, and market accessibility) by identifying regions with similar dominant constraints. For each combination of dominant constraints, we identified management strategies needed to tackle the prevailing single or multiple constraints (Fig 1 and S2 Text). These management strategies are a novel approach to overcome and reduce yield gaps considering the biophysical and socioeconomic factors that have an impact on crop yields. For attaining high-input yields, implementation of these strategies is needed in addition to application of adequate nutrients and use of high yielding crop varieties. Moreover, we estimated additional crop calories that can be produced by implementing these strategies based on the differences between the current and the high-input potential crop calorie production.
Nutrient management plays a crucial role in closing yield gaps . To obtain crop yields constantly above the low-input levels, fertilizer application is needed in addition to natural nutrient regeneration. Hence, we quantified the amount of fertilizers required to attain high-input potential crop yields considering differences in crop production under low and high input levels. As nutrients absorbed by crops are stored in crop products (e.g., grain) and residues (e.g., straw), we considered differences between yields and residues of the 16 crop types from GAEZv3.0 for high and low input levels, also accounting for fallow period requirements. GAEZv3.0 provides crop specific fallow period requirements for high and low input levels by crop group, by soil type and by climatic condition. A low-input farming system requires a longer fallow period for natural nutrient regeneration that is substituted by fertilizer application in high-input agriculture, shortening the fallow period requirement. We calculated residue for a crop type based on its yield and harvest index . Afterwards, we estimated the amount of additional crop nutrient uptake in crop yields and residues while attaining high-input potential yields. For this, we multiplied the crop harvested area by the differences in crop yields and residues between low and high input levels, and by the crop specific nutrients uptake in yield and in residue, respectively (S1 Table). We assumed that both crop products and residues are removed from the fields. Hence, nutrient removal that has to be replenished by fertilizers (organic or chemical), is equal to the total nutrient uptake in yields and residues. Since fertilizers applied to crops may get lost due to leaching and volatilization, the total fertilizers required also varies depending on fertilizer application efficiencies. By this, we estimated the quantities of three macro-nutrients required (N, P2O5, and K2O) to achieve the potential high-input yields (see S3 Text) assuming that micro nutrient constraints are tackled in fertilizer specific nutrient compositions.
Here, we showed that climate patterns, specifically spring precipitation and average summer and winter temperatures, were key drivers of interannual and spatial variation in abundance of wild bees in temperate ecosystems. In the Northeast USA, past trends and future predictions show a changing climate with warmer winters, more intense precipitation in winter and spring, and longer growing seasons with higher maximum temperatures (Easterling et al., 2017 Lynch et al., 2016 Thibeault & Seth, 2014 ). In almost all our analyses, these conditions were associated with lower abundance of wild bees. Wild-bee richness results were more mixed, including neutral and positive relationships with temperature and precipitation patterns predicted to increase in the future. In the Northeast USA, combined with continued urbanization, changing climate imposes a significant threat to wild-bee communities.
The relationship between climate conditions and wild-bee abundance and richness deserves more research attention. We especially recommend research to elucidate the mechanisms underlying these variable relationships and implications for fluctuating wild-bee abundance for pollination service provisioning. A more mechanistic understanding of direct and indirect effects of temperature and precipitation on wild bees, and how these interact with land use, is crucial to inform climate-resilient conservation of bee populations. By including climate variables, landscape pollination models and decision-support tools would likely more accurately predict interannual variation in wild-bee abundance and effects on pollination services for crops and wild-plant communities.