Climate change and Crop farming:

Drip - Fertigation assisted Precision Farming helps to reduce the negative impact of crop production on the environment.
By: Dr.P.Soman, Jain Irrigation Systems, Ltd., Posted on: May 2021

Conventional crop production is found to add to climate change phenomenon. Inputs and processes associated with irrigation, fertilizer application, use of pesticides etc. are affecting the environment more detrimentally; 1 by the inputs per se or 2. by the derivatives formed in the soil system like production of CO2 or other Greenhouse gases (GHG). For example, excess use of Urea (N-source fertilizer when applied in 1 or 2 splits) in rice paddies result in NO2 pollution of water bodies; or excess irrigation causing standing water paves the way for high emission of Methane gas, a potent GHG. The Green revolution of the sixties are lauded for the timely interventions to enhance grain production in India at a time the country faced acute shortage of food and food security depended on outside assistance. The introduction of HYV (High Yielding Varieties) seeds of wheat and rice and large scale growing of these crops with flood irrigation and excess of urea input, certainly produced more food grain. But it also resulted in several environmental issues.

Green revolution – Environmental impact

A very visible example that India and the world experienced.

The Green Revolution has transformed India to a food grain surplus country from a deficit one. No other activity has such immense impact on the socio-economic development of the people as the Green Revolution. Intensification of agriculture over the years has led to overall degradation of the fragile agro-ecosystem. Loss of soil fertility, erosion of soil, soil toxicity, diminishing water resources, pollution of underground water, salinity of soil and underground water, and global warming are some of the negative impacts of over- adoption of agricultural technologies by the farmers to make the Green Revolution successful.

Indiscriminate and disproportionate use of chemicals pollutes the soil, air and water and feed and fodders offered to animals. Various scientific studies and surveys conducted on fertilizer and pesticide residues during last 45 years indicate the presence of residues of fertilizers and pesticides like nitrates, organochlorines, organophosphates, synthetic pyrethroids and carbamates at higher level than permissible limit in milk, dairy products, water, fodder, livestock feeds and other food products.

For example, urea, a nitrogen-rich fertilizer, when used much more than the recommended doses and not in balance with other crop nutrients, contribute to global warming. The extent of systematic damages caused in the process of Green Revolution to the soil, groundwater, and ecosystem is still not fully quantified. It could lead to irreversible consequence to the life of the people who are benefited once if the timely, adequate and sustainable measures are not taken up to mitigate the harm done already.

Environmental impacts of GR have been mixed. On one hand Green Revolution driven crop intensification saved new land from conversion to agriculture, a known source of greenhouse gas emissions and driver of climate change, and allowed for the release of marginal lands out of agricultural production into providing alternative ecosystem services, such as the regeneration of forest cover. At the same time use of HYVs which are more responsive to external inputs were central to the productivity achievements; however, there were no efforts to incentivize judicious use of inputs. This resulted in unintended consequences in water use, soil degradation, and chemical runoff etc. those had serious environmental impacts beyond the areas cultivated.

A visible example of this situation is the slowdown in yield growth that has been observed since the mid-1980s. These environmental costs are widely recognized as a potential threat to the long-term sustainability and replication of the success of GR. The environmental consequences were not caused by the GR technology per se but rather, the policy environment that promoted injudicious and overuse of inputs and expansion of cultivation into areas that could not sustain high levels of intensification.

How micro irrigation assisted precision farming provides opportunities to reduce the effect of cropping on climate change.

Agriculture is almost the biggest victim of climate change, but at the same time, agriculture is one of the main sources of greenhouse gases (it produces almost a quarter of the emissions). It is understood that climate change has occurred mainly due to the burning of oil, gas and coal. But agricultural production also significantly affect the situation on the Planet. The main carbon dioxide absorbers are forest and soil. About 10 billion trees are cut down every year for using lands for agricultural needs, and soils, due to improper processing, not only stop absorbing CO 2 , but, on the contrary, produce greenhouse gases (due to the abuse of fertilizers).

How traditional farming causes environmental issues.

The use of agricultural inputs such as mineral fertilizers, organic fertilizers, herbicides and pesticides is important to guarantee threshold levels of yields and crop quality. But providing large amounts of inputs to crops and with improper timing could cause disorders in the ecosystem. This may affect both food production within fields and the environment on a larger scale.

Examples of environmental damage are,

  1. Greenhouse gas emissions (GHG)
  2. Accumulation leaching of chemical compounds in soil and water reservoirs (Pollution)
  3. Changing ecosystem properties (Climate change)
  4. Reduced biodiversity (Concentrating on few crops and limited crop varieties).

Climate change has already affected every farmer on the planet. What role exact technologies will play in such conditions? Adopt new technologies and innovations that can optimize inputs and reduce the negative impact on the ecosystem and result in optimizing production costs. Use of fertilizers ensures crop productivity. But excessive use of these will result in environment degradation.

The goal of precision farming is to achieve two contrasting goals- to increase productivity and reduce potential environmental risk.

  • Monitor the soil and plant physicochemical parameters: by analysis and placing sensors (electrical conductivity, nitrates, temperature, evapotranspiration, radiation, leaf and soil moisture, etc.) the optimal conditions for plant growth can be achieved.
  • Obtain data in real time: the application of sensing devices in the fields will allow a continuous monitoring of the chosen parameters and will offer real time data ensuring an updated status of the field and plant parameters at all time
  • Provide better information for management decisions.
  • Adopt micro irrigation and fertigation with scientifically prepared schedules of water and fertilizer application.
  • Save time and costs: reduce fertilizer and chemical application costs, reduce pollution through less use of chemicals
  • Provide better farm records essential for sale and succession
  • Can be integrated with any farm management software, to make all activities on farm more easy and to improve farm productivity.

Collectively adoption and committed practice of the above steps is Precision farming (PF).

For example, benefits due to reduced overlap of spraying were typically in the order of 10% savings on spraying costs. Other important benefits are: less fuel use, less soil compaction, less hired labour requirement and more timely sowing.

So, to farmers and land owners who decide to use technology to manage their fields, precision farming seems to bring many benefits, and ultimately increase of profit.

Precision agriculture technologies are focused on the detailed management of in-field variability. Since these site-specific technologies allow for an accurate distribution of agricultural inputs, such optimization can potentially lead a mitigation of the negative environmental impacts arising from excessive use of agricultural inputs associated with traditional agricultural activities. Overall, according to the definition provided precision agriculture entails intrinsic positive environmental impact, being able to apply inputs at the right rate, at the right time, and with the right placement.

Though there is a growing attention towards Precision farming technologies (PFT), their environmental impacts have not, in general, been systematically analysed and discussed. To date, the scientific interest has mainly focused on two topics, (i) the study of the agronomic and economic impacts related to the use of a given PFT, and (ii) the issue of pesticides and herbicides leaching ecosystems, considered serious threats for the environment. It is also acknowledged that a significant reduction of environmental impact due to the reduction in nitrogen, lime and pesticides inputs happens in PF.

Let us discuss the potential environmental benefits from the adoption of Precision farming technologies, like implementing an irrigation schedule based on crop evapo-transpiration and fertigation schedule where nutrient application rate and time matches the crops' physiological need for nutrients, type and rate. In the long run and particularly, the agriculture activities of nitrogen application, pesticides application, lime application, manure application and herbicide application, which can be carried out by means of Variant Rate technologies (VT) with the support of guidance and monitoring technologies (sensors).

COTTON WATER AND POWER USE (Maharashtra)

Drip system

Volume of water for flood irrigation
liter/ ac

Volume of water under drip
lit/ac

Power used per
acre/season
KwH

Reduction in water Use in Drip irrigated crop
liter/ac

Power saved due to drip
KwH

yield increase
t/ac due todrip

16 mm,50 cm, 4 lph

45,00,000

30,36,000

By Flood-1156

14,64,000

386

1.0-1.2

   

By Drip- 770

     

Water productivity under Drip 0.82 kg cotton/1000 liter

Water productivity under Flood 0.16 kg cotton/1000 liter

Power productivity of Cotton Under Drip 3.25 kg/ KwH

Power productivity of Cotton Under Flood 0.61 kg/ KwH

Precision nutrient application to rhizosphere by fertigation vs conventional soil loading of excess fertilizer

Farmers apply nutrients on their fields in the form of chemical fertilizers and animal manure, which provide crops with the nitrogen and phosphorus necessary to grow and produce the food we eat. However, when nitrogen and phosphorus are not fully utilized by the growing plants, they can be lost from the farm fields and negatively impact air and downstream water quality.

Large quantity of Urea applied into the soil can cause negative effects in the soil, plant and the environment. Nitrate formed from Urea is highly mobile and leaches into water bodies and cause environmental impact. The rate of application has to be controlled and this occurs when it is fertigated in frequent intervals –daily dose or two doses in a week etc. The following details show the negative effect of nitrogen application in traditional agriculture.

Excess urea causes adverse effects on soil, crop quality and overall ecosystem besides leading high insect and disease pests. The high activity ureolytic bacteria in the soil generates more ammonia in the soil by rapid urea degradation. Plants will be detrimentally affected by the excess ammonia and CO2 generated from this reaction. Ammonia leached to water bodies will affect fish life. Even concentrations of ammonia as low as 0.02 ppm can be lethal. Volatilization of ammonia to the atmosphere may become a water quality problem when it is returned to the earth dissolved in rainfall.

High levels of nitrates can be toxic to livestock and humans. Nitrates are not adsorbed to soil materials, so they may leach to groundwater. In some instances, stored or soil-applied manures or nitrogen fertilizers have caused high concentrations of nitrates in water. Because nitrates freely leach down through the soil profile, nitrogen that is not used for crop growth can reach the groundwater easily.

Balafoutis et al. (2017) evaluated the differences between conventional viticulture practices and precision viticulture techniques in terms of GHG emissions and carbon footprint, finding significant potential. The study reported a cut of 34% in nitrous oxide emissions resulting from site-specific fertilizer application.

Fertigation helps in actual reduction of fertilizer load on to the soil still increasing yield.

  • Fertigation with a scientifically designed schedule allows nutrient application in the correct dosage at appropriate time of its growth.

  • Very low rates of nutirents at the early growth stage

  • Rates increases as the flower and fruit load increases

  • Again rates reduced as the crop goes thru senescence and approches end of growth

  • Crop gets its requirement satisfied all through its growing cycle.

Because of the above strict regimen soil is never loaded with excess fertilizer. This alone is adding to lower rate of residual accumulation in the soil and ground water .

CROP

Reduced fertilizer Use (%) in Fertigation compared to conventional application (100%)

Increase in yield despite reduction in fertilizer use (%)

Okra

60

18

Onion

60

16

Broccoli

60

10

Banana

80

11

Potato

60

30

Tomato

60

33

Data from IARI (TBS Rajput 2002) re interpreted here.

Willis et al. (1991) showed that a fertigation frequency of only 5 times a year resulted in higher soil ammonium and nitrate levels in the top 15 cm within 1 week after fertilization compared with fertigating 10 or 30 times a year. Alva et al. (1998) also found that an increased fertigation frequency substantially minimized nitrate-N movement under micro-sprinkler-irrigated mature orange trees.

A careful consideration of nutrient concentrations in fertigation programs is also required to contain nutrient levels within acceptable contaminant limits. The use of frequent fertigation, combined with improved irrigation scheduling, results in improved fertilizer uptake efficiency, and enhanced water use efficiency, increased residence time of nutrients in the root zone, and reduced potential for groundwater pollution. Compared with conventional ground application, fertigation can produce similar or better growth as well as yield and fruit quality with lesser amounts of fertilizer.

In drip –fertigation, water, fertilizer placement, and application frequency are managed more efficiently compared with a dry fertilization program. Productivity gains with irrigation and fertigation, using the same fertilizer doses, increased nutrient use efficiency 25%, compared with flood irrigation and solid fertilizer direct to the soil. For this reason, it is recommended to reduce N and K doses by 20-25% when nutrients are applied through fertigation in relation to the nutrient levels recommended for direct solid fertilizer application to the soil. This observation is reiterated in our own field experiments on several crops (see below where Cashew and Pomegrante data are given).

Table 3 given below reports the benefits associated to site-specific nitrogen application. From the analysis, it emerges that applying high fertilizer rates to maximize short-term economic yield can cause long-term harm to the environment, with negative consequences including air pollution.

Table 3. Site specific precision fertilizer application and how it reduces climate changing factors (summary of a review by Marco Medici et al. 2019-Environmental benefits of Precision Agriculture Adoption- A review of 40 studies on the topic obtained after scanning 1417 published papers)

Snyder et al. (2009); Ma et al. 2010 Air quality Nitrogen emissions
(decrease)
Sehy et al. (2003) Air quality Nitrogen emissions (N2O) (decrease)
Balafoutis et al. (2017) Air quality Carbon footprint (GHG) (decrease)
Dobermann (2007); Soil quality Compound presence (NO3-N)(decrease)
Galloway et al. (2003) Water quality Compound leaching (NO2)(decrease)

Estimates of N2O emissions from cultivated soils have been reported. As fertilizer additions increase, N2O emissions appear to remain quite static across a broad range of rates (roughly between 90 and 150 kg N ha-1), maybe near the crop demand levels. At higher N rates, emissions tend to increase nonlinearly. How an increase in N input beyond 90 kg N ha-1 would result in considerable N2O emission, even with marginal yield improvement. Improving the efficiency of N use can potentially reduce also potential residual NO3-N in the soil profile while minimizing the 'cascade' to water resources in terms of compound (nitrate) leaching.

Phosphorus (P) is a naturally occurring element that exists in minerals, soil, living organisms and water. Plant growth and development require phosphorus, like nitrogen, in large amounts. The forms of phosphorus present in soil can include organic, soluble or "bound" forms. Understanding the relationship among these forms of phosphorus is necessary to understand plants' utilization of phosphorus and the extent to which phosphorus can move within the environment. Note that phosphorus is the least mobile of the major plant nutrients. ■ Organic phosphorus — a part of all living organisms, including microbial tissues and plant residue. About two-thirds of the phosphorus in fresh manure is in the organic form. ■ Soluble phosphorus — sometimes called available inorganic phosphorus. It can include small amounts of organic phosphorus, as well as orthophosphate, the form taken up by plants. It also is the form subject to loss by dissolution in runoff and, to a lesser extent, leaching.

When fertilizer or manure (both containing mostly soluble phosphorus) is added to soil, the soil's pool of soluble phosphorus increases. With time, soluble phosphorus is transformed slowly to less- soluble (less plant-available) forms. ■ Attached or "bound" phosphorus — unavailable inorganic phosphorus.

Potassium (K) can be lost from the soil by leaching, though amounts are generally small, with the exception of sandy soils. Average leaching losses, measured in terms of potash (K 2 O), of around 1.2 kg K 2 O/ha per 100 mm drainage have been reported for loams and clay soils. In experiments in Denmark, leaching losses of 0.6 kg K 2 O/ha and 8.4 kg K 2 O/ha per 100 mm drainage were found for soils with 24% and 5% clay respectively.

The concentration of K in water draining from agricultural land in the UK rarely exceeds 3 mg K/litre and that in rivers rarely approaches 10 mg K/litre. The EC of Drinking Water Directive set a maximum admissible limit of 12 mg K/litre with a guideline of 10 mg K/litre. These limits do not appear to have any toxicological or other basis as they are vastly exceeded in many common drinks (e.g. 1570 mg K/kg in milk and fruit juices, 880 mg K/kg in coffee). Losses of potassium to water are not of environmental concern in this case.
Potassium is not lost to the air from soil.

But a deficiency of potassium can affect nitrogen uptake and transport from roots to shoots, protein development and yield in a crop. Potassium is an activator for some forty enzymes, and is involved in the development of proteins from nitrate. Inadequate potassium leads to an accumulation of nitrate in the roots which can restrict further uptake of nitrogen from the soil. This has a subsequent effect on the efficiency of utilisation of nitrogen applied in either fertilisers or manures. Poor efficiency of nitrogen utilisation will lead to unnecessary nitrogen residues in the soil increasing the risk of nitrate leaching. Thus precision fertigation of potassium fertilizers has an indirect effect on soil and water body health.

How can these negative effects be reduced or annulled.

Simply by need based (Crop need assessment) fertilizer application through fertigation where very low concentrations (rates) of the fertilizers are applied to the rhizosphere in large number of doses during the crop growing duration. Fertigation schedules prepared by Jain agronomist provides this opportunity. The result is high nutrient use efficiencies and no or nil effect nutrient on the environment. This practice helps in retarding the rapidity of climate change. In many crops it has been found that real time reduction of the total quantum of various fertilizers up to 25% of the recommended quantities (recommendations by Public institutions (universities/Crop research centers) can result in higher crop yields (productivity).

Cashew

Pomegranate

In both cases, of Cashew and Pomegranate, full RDF directly dry applied to the soil is least efficient on account of yield of the crops. And large quantity of NPK is lost to the soil and environment. Fertigation in very low rate of application and in large number of doses increases yield and fertilizer use efficiency. The data also show that for the highest yield one need to apply only 50 % (Pomegranate) and 75 % (Cashew) of the RDF; a direct cut on the fertilizer load into the soil.

In general about nutrient management, farmers could adopt plans in which soil testing is performed in order to determine residual nutrients in the soil and then filling in the deficit with appropriate nutrients rates. Positive effects resulting from the use of fertigation and Variable Rate application technology (both soil nutrient map-based application systems and real-time sensor-based systems).

Pesticide application. Relevant savings of pesticides in comparison with traditional pesticides applications have been acknowledged, with no yield limitation (Aita et al. 2015). The use of VR technology paves the way to an optimal use of pesticides also, leading, on the one hand, to the reduction of agricultural and human pests, and, on the other hand, to the control of the impact of treatments on human health and on the environment, in terms of soil and water contamination by chemical compounds. IPM is an integral part of Jain agronomy support to the micro irrigation adopted farmers.

A reduction in herbicide use is highly expected, considering also that a small weed presence (up to 20-30%) does not significantly alter crop production, as per the ETL estimations. Besides saving inputs, need based herbicide application could alleviate also weed resistance problems caused by massive use of herbicides. Studies also highlight another mitigation effect of PATs related to the increased richness and diversity of non-target plants. Precise weed control like the mechanical and the thermal approaches do not imply any use of herbicide and hence do not figure in the climate change impact.

 

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