Agriculture is liable for climate change as its activities accounts for nearly 13.5% of the total global anthropogenic Greenhouse Gas (GHG) emissions [1
]. During the last decade, there is a trend of GHG emissions reduction in the agricultural sector, but more effort on this direction should be made to fulfil global climate commitments. The main contribution of agriculture to GHG emissions is related to cropland soil, enteric fermentation and manure management [2
The application of precision agriculture (PA) practices, using the large reservoir of Precision Agriculture Technologies (PATs) in agricultural field operations could positively contribute to GHG emission reduction due to: (i) the enhancement of the ability of soils to operate as carbon stock reserve [2
] by less tillage [3
] and reduced nitrogen fertilization [4
]; (ii) the reduction of fuel consumption through less in-field operations with the tractor (direct GHG decrease); and (iii) the reduction of inputs for the agricultural field operations (indirect GHG decrease) [6
]. On the other hand, these practices affect farm productivity by optimizing agricultural inputs producing higher or equal yields with lower cost than conventional practices. Therefore, GHG mitigation measures that refer to new technologies and techniques on all agricultural practices (precision/variable rate sowing/planting, fertilizing, spraying and irrigation) can reduce significantly the amount of inputs that are responsible for GHG contribution and could help on the goal of minimum climate change impact of agriculture, always taking into account that crop production should be maintained or even increased in the challenge of ensuring food security and safety for human food consumption.
Current use of PA practices in the world and EU basis is in general unclear. There was a strong uptake of PATs during the 1990s in North America, mainly because of the rise of information technology and the fact that US and Canadian agriculture had the appropriate characteristics to promote new technologies promising better economic results. Those characteristics were: (i) the large farm sizes; (ii) the organised extension system mainly by the government and universities; (iii) the farmers/entrepreneurs willingness for progress and technology adoption; (iv) the high income; (v) the possibility of financing investment; and (vi) the limited or absent subsidies in agricultural products [7
]. PA growth rate flattened during the first years of 2000s, because the results (productivity increase, inputs and fuel use reduction, ease of use, low maintenance, and compatibility between brands) were not as positive as expected by the agricultural community. However, PATs are currently taking up again, because technology problems have been gradually resolved and more tangible economic results have been shown at farm level (e.g., profit increase). In 2014, PA global market already amounted to €2.3 billion, with an expected annual growth rate of 12% through 2020 with the mature US and European markets considered the most promising [9
However, most practitioners do not have a clear perspective of the benefits of PATs in agricultural production and do not consider the environmental reimbursements that their use could provide [11
]. There is a need to produce evidence of the actual impact of these technologies on GHG emissions, farm productivity and economics. Therefore, the objective of this paper was to identify and describe the PATs that possess the capacity to have positive impact on GHG emissions produced from the agricultural sector in combination with farm productivity and income sustenance or improvement.
In the first section, the main sources of GHG emissions in the agricultural sector are described, while the second section analyses the GHG mitigation practices. Subsequently, the typology of PATs is presented to sort the PATs that have a potential direct positive impact on GHG emission mitigation combined with improved or at least stable farm productivity and economics. Then, a list of the most influencing PATs is presented with a short description of their technical characteristics and its GHG emissions impacts. It should be noted that literature on PATs impact on GHG emissions is highly limited and therefore the discussion on the mitigation capacity is mainly based on the reduction of agricultural inputs (e.g., fertilisers, pesticides, fuel, and water) that can be achieved using PATs. Subsequently, the farm productivity and economic impacts of acquiring and using PATs are analysed and discussed. Finally, a conclusion of the importance of PATs on both reducing GHG emissions and maintaining or increasing farm productivity and income is given.
2. Main Sources of Agricultural GHG Emissions
The major GHGs produced in the agricultural sector are methane (CH4
), nitrous oxide (N2
O) and carbon dioxide (CO2
is mainly produced from the anaerobic decomposition of organic matter during enteric fermentation and manure management, but also from paddy rice cultivation; N2
O arise from the microbial transformation of N in soils and manures (during the application of manure and synthetic fertiliser to land) and via urine and dung deposited by grazing animals; and CO2
arising from: (i) energy use pre-farm, on-farm and post-farm; and (ii) from changes in above and below ground carbon stocks induced by land use and land use change [15
The agricultural sector contributes to the production of 25% of CO2
, 50% of CH4
, and 70% of N2
O emissions in a global basis summing up to nearly 13.5% of the total global anthropogenic GHG emissions, as stated above [1
]. However, in OECD member countries, agriculture produces 8% of the total GHG emissions with a decline between 2000 and 2010 by an average of 0.4% per annum with simultaneous agricultural production increase of 1.6% per annum, which is interpreted into 1.97% of GHG emission intensity reduction. Therefore, the developed country members of OECD are trying to achieve synchronized GHG mitigation and productivity increase, which is the ideal situation and is defined as the “absolute decoupling” [16
The larger agricultural economies generally produce higher levels of GHG emissions, but they do not follow the same pattern. An explanation of this statement is that, for example, France and Germany together accounted for around one third of the EU-28 agricultural GHG emissions, while the combination of the UK, Spain, Poland and Italy covered an additional third of the total. To decrease EU agriculture impact on GHG emissions, the EU Roadmap for moving to a low carbon economy recommends a reduction target of agricultural GHG emissions by 36–37% until 2030, and a more ambitious one (42–49%) for 2050 in comparison to 1990 levels [17
O is the main GHG related to agricultural soil emissions, essentially due to microbial transformation of nitrogen in the soil (the process of nitrification and denitrification to be analysed later in this paper). This concerns nitrogen mineral fertilisers, manure spreading and nitrogen from crop residues incorporated into the soil or lixiviation of surplus nitrogen. N2
O has high Global Warming Potential (298 times higher than CO2
) and it should be minimized to reduce agricultural GHG emissions in total. An example of favourable N2
O emissions increase conditions is when soil temperature is increased and high moisture conditions exist during cooler months. Another example would be the increase of N2
O from upland agricultural soils due to CO2
]. The application of mineral nitrogen in the form of chemical fertilisers would also increase the N2
Enteric fermentation, which is a natural part of the digestive process for ruminants, is the most important CH4
emission producer. CH4
is also produced during manure storage (decomposition). There are several studies targeting on CH4
] and its mitigation potential from rice fields, mainly through water [20
], fertiliser, and manure management [21
emissions increase when mulching and organic manure are applied in soils [22
]. On the other hand, midseason drainage of rice farms can reduce CH4
emissions significantly [23
]. Aerobic soils may act as CH4
] or emission sources [25
As for CO2
, direct combustion of hydrocarbons together with soil respiration and residual biomass decomposition are the main sources of emissions. However, the majority of the farm operations and inputs (e.g., fertilisers, pesticides, and energy) also have embodied CO2
content. Direct CO2
emissions produced by agriculture as well as indirect CO2
emissions from processing of inputs at farm level showed that this gas can represent between 10% and 20% of the total GHG emissions in agriculture [2
3. Greenhouse Gases Mitigation Practices
Climate change can be mitigated through the reduction of GHG emissions, the enhancement of GHG removals and the avoidance or displacement of emissions [24
]. Mismanagement of carbon (C) and nitrogen (N) flows in the agricultural system is the reason for GHG overproduction. There are methods and technologies that reduce GHG emissions, such as the timely and accurate application of nitrogen fertilization that reduces N2
]. Regarding enhancing GHG removals, any agricultural practice that increases photosynthetic processes or slows the return of stored C in organic biomass can be considered as C sequestration method [28
]. In addition, GHG emissions can be avoided or displaced by the conversion of residual agricultural biomass into biofuel of any type [29
], where in reality this energy source replace fossil fuels of the same energy content.
However, the mechanisms that reduce one GHG can sometimes affect another GHG in a negative way through different mechanisms resulting in combined effects that are unknown [31
]. For instance, no-tillage practices, which can potentially reduce GHG emissions by 20.6–23.7% compared to conventional tillage [33
], may have unanticipated and unwanted effects on other sources or sinks of GHG. If, for example, soil water conservation associated with no-till were to provide more moisture for nitrifying and denitrifying bacteria as well as plants, then production of N2
O might increase, offsetting some or all of the mitigation potential of carbon storage [34
Smith et al. (2008) [24
] listed the GHG emissions mitigation measures in seven categories that include different practices: (i) cropland management (nutrient management, tillage/residue management, water management, rise management, agroforestry, set-aside, and land-use change); (ii) grazing land management/pasture improvement (grazing intensity, increased productivity through fertilisation, nutrient management, fire management, and species introduction including legumes); (iii) management of organic soils (avoid drainage of wetlands); (iv) restoration of degraded lands (erosion control, organic amendments, and nutrient amendments); (v) livestock management (improved feeding practices, specific agents and dietary additives, longer term structural and management changes and animal breeding); (vi) manure/biosolid management (improved storage and handling, anaerobic digestion, and more efficient use as nutrient source); and (vii) bioenergy production (energy crops, solid, liquid, biogas, and residues).
PA for crop farming is included in the first category with a special interest on nutrient management and water management. Agricultural GHG emission mitigation should be focused on increasing the efficiency of agriculture to reduce future land conversion, and also on reducing N2
O emissions from soil N management [35
]. Eory and Moran (2012) [35
] considered four mitigation measures connected with PA (improved timing of mineral nitrogen (N) application, improved timing of organic N application, full allowance of manure N supply and avoiding N excess). All of them showed considerable GHG abatement potential with “Improved timing of mineral N application” reaching 0.3 tCO2
A report from the UK Government [36
] analysing agricultural emissions in the UK reported that, to reduce national GHG emissions by 3 MtCO2
-eq by 2020 compared to 2007, the most promising method is nutrient management (it can reach 1.4 MtCO2
-eq), followed by the use of plants with improved nitrogen use efficiency (potential of 0.8 MtCO2
-eq) and improved land and soil management (up to 0.45 MtCO2
-eq). This work shows the potential of PA practices that are directly connected with nutrient, land and soil management.
The European Commission Climate Action also proposes GHG mitigation measures related to farming practices, such as seeding/planting, harvesting, irrigation and fertilisation of existing crops, use of different varieties, diversify crops, implement management practices [37
]. EU seeks for sustainable agricultural schemes through the new Common Agricultural Policy (CAP). Natural resources are depleting and agriculture has to improve its environmental performance. Sustainable management of natural resources and climate action represent one of the three main objectives of the CAP [38
]. Improved sustainability will be achieved firstly by covering certain environmental requirements and obligations in order to receive full CAP funding. Secondly, from 2015 onwards, the CAP introduced a new policy instrument, the Green Direct Payment, that is granted only when there is simultaneous crop diversification, ecological focus areas and permanent grassland, with environmental benefits on biodiversity, water and soil quality, carbon sequestration and landscapes. It represents 30% of the direct payment budget and it is compulsory. Finally, rural development is vital for achieving the environmental objectives of the CAP and combating climate change, as at least 30% of the budget of each rural development programme must be reserved for targeted measures on this direction. All these policy instruments are accompanied by related training measures and other support from the Farm Advisory System, insights gained from the Innovation Partnership and applied research, which would help farmers to implement appropriate solutions for their specific situations. Proposed solutions on the farm level are the adjustment of farm operations timing; the improvement of the effectiveness of pest and disease control through better monitoring, diversified crop rotations, or integrated pest management methods; the use of water more efficiently by reducing water losses; improving irrigation practices; recycling or storing water; and the improvement of soil management by increasing water retention to conserve soil moisture.
PATs could participate in the achievement of agricultural sustainability as they increase the efficiency of most agricultural practices by reducing or redistributing inputs to address the real requirements of the crop. It is anticipated that the new CAP will promote further PATs as one of the methods to increase or maintain productivity with simultaneous reduction of environmental impacts, and in specific GHG emissions.
4. Typology of Precision Agriculture Technologies
In the literature, there are only three attempts to provide a typology of PATs. One of the most prominent studies on PA [12
] classifies PATs in three main categories: Hardware and sensors
(i.e., positioning and guidance, crop sensing for water stress, nutrients and yield sensing, environmental sensing, seed bed preparation, and fertiliser placement in the soil profile); Data Analysis and Decision Support Systems
(i.e., protocols and standards for field data layers production, methods for data analysis for delineation of management zones, and easy-to-use software); and Commodity and whole-farm focus
(i.e., development of DSS to apply commercially in farms including environmental impact assessment, and apply PA at farm level and not at field level). Zarco-Tejada et al. (2014) [14
] categorised PATs for crop and livestock farming in a linear manner following the timeline of use of the technologies ending up in three categories, namely Remote sensing
; Guidance systems
; and Variable rate applications
Finally, Schwarz et al. (2011) [39
] have provided the most comprehensive typology of PATs (selected to be used in this work, see Figure 1
), divided into three main categories: Guidance systems
(i.e., hard- and software that guide tractors and implements over a field), which include all forms of automatic steering/guidance for tractors and self-propelled agricultural machinery, such as driver assistance, machine guidance, controlled traffic farming; Recording technologies
(i.e., sensors mounted on ground-based stations, rolling, airborne or satellite platforms, and gathering spatial information), which include soil mapping, soil moisture mapping, canopy mapping, yield mapping, etc.; and Reacting technologies
(i.e., implements, hard- and software that together can vary the placement of agricultural inputs in the field), which include technologies such as variable rate irrigation and weeding and variable rate application of seeds, fertiliser and pesticides.
Guidance technologies can be used for any agricultural practice application (including traditional practices) focusing on precise machinery movement within and between fields with tangible results in reduced overlapping causing lower input use (seeds, fertilisers, and pesticides) in parallel with decreased self-propelled machinery fuel consumption. Recording technologies are required in order to receive information from the field (before, during and after the crop period) and after processing, extract the data useful for any kind of PA application. Reacting technologies are supposed to use the data produced by the recording systems and minimize all inputs (seeds, fertilisers, pesticides, and water) in the optimum quantity required by the crop to grow. The right combination of these three categories is expected to increase or at least maintain yield with the advantage of higher quality and minimum environmental impact.
All three categories of PATs require the use of Global Navigation Satellite Systems (GNSSs), as shown in the figure. Recording technologies and GNSSs remain supportive in the PA process and they will not be analysed in the next section of this paper. Hence, reacting technologies and guidance systems were selected to be analysed and their potential to reduce GHG emissions and improve farm productivity and income was assessed.
Climate change is a fact, and anthropogenic activities are one of the parameters accelerating the phenomenon. Through the years, agriculture did not receive great attention in terms of GHG emission production, as yield increase was the target. In the recent past, analysis of the impact of this sector on climate change has been executed and several mitigation measures were proposed.
PA has several positive impacts on agricultural systems translated to increased farm productivity and income and recently there is significant interest on the possible GHG emission mitigation using PATs. However, literature is limited on data regarding the effect of PA on climate change. All categories of PATs (guidance, recording, and reacting) contribute to the reduction of GHG emissions due to their interconnections and it is difficult to separate them according to importance. Recording and GNSS technologies are supportive in the PA process, while reacting technologies and guidance systems have a direct visible result on the agricultural system that are applied on. Hence, these PATs were analysed according to their potential to reduce GHG emissions and improve farm productivity and income.
Variable rate nutrient application (VRNA) technologies can reduce the fertilizer quantities applied in modern agriculture by using technology to cover site-specific nutrient needs. VRNA can be applied to all nutrient application, with nitrogen being the most important to be regulated through these technologies as it is the element that is mostly used for crop growth increase and covers the highest percentage of fertilizers globally. Therefore, VRNA can significantly contribute in accurate nutrient management, which can be translated to reduction of GHG emissions and especially nitrogen that is responsible for N2O release (the GHG derived from agricultural activities with the highest global warming potential). They can also affect positively farm productivity and income by increasing final yield especially in low productivity sections of a farm and by reducing the fertilization costs that follows optimized application of nitrogen according to the plants’ needs.
Variable rate irrigation (VRI) systems have the following GHG emission reduction potential, as its impact is dual: primarily, the decrease of irrigated water reduces the energy for water pumping, and, secondly, the optimum irrigation scheduling affect significantly the release of GHG emissions derived from fertilisers through the soil (mainly N2O). In terms of productivity, the impact is also significant, particularly in dry areas, as irrigation scheduling kai dosage can be optimized resulting in economic benefits (lower pumping costs combined with higher yields).
Controlled Traffic Farming (CTF) and machine guidance (MG) limit the use of tractors to only the necessary passes through the fields avoiding overlapping with respective decrease in agricultural inputs and fuel (translated into GHG emissions reduction and lower cost of production). Variable rate pesticide application (VRPA) is also expected to have GHG reduction potential by reducing the pesticide application and its industrial production. However, the actual environmental effect can be extremely significant, but through lower chemical substances application that contaminates all natural resources (water, air, and soil). The effect on farm economics is also major, especially in crops that receive many chemical applications, such as herbicides and fungicides.
Variable rate planting/seeding (VRP/VRS) and precision physical weeding (PPW) show lower, but not irrelevant GHG emission mitigation. VRP/VRS is mainly important for optimising plant density in the field that can increase farm productivity, while the reduction in seed/plant population is associated with GHG emissions during their production. PPW reduces pesticide application and fuel used for flame burning of weeds.
It is believed that PA adoption can be increased significantly if the PATs available in the market would combine more precise and robust sensors specialised for each activity and the end-users (farmers) will receive quantified information of the farm profit augmentation and the positive sustainability impact, combined with reduced investment cost for PAT purchase. Therefore, there is a necessity that more research should be carried out on quantifying the impact of PATs on GHG emissions reduction and the respective productivity and income influence, as there is strong evidence of the contribution of PATs to climate change mitigation and the increase of production efficiency (yield and economics). Specific attention should be given to research of different macronutrients impact (direct and indirect) on GHG emissions by regulating the status of each element in crops. Optimised methods of application could maintain the amount of essential nutrients in desired quantity that will primarily reduce undesired yield loss that could be due to unknown stresses coming from unbalanced nutrient combination, and secondly will improve the carbon footprint of crops.