Promoting Healthy Environment through Enhanced Nitrogen Use Efficiency and Improved Crop Yields by using Calcium Carbide

By Ahmad Zeshan¹, Zia-ul-Hassan Shah¹ and Dr. Muhammad Arshad²
December 2006

  1. Agriculture Chemist (Soils), presently Higher Education Commission Pakistan PhD Scholars
  2. Professor and Director, PhD from University of California, Riverside, USA

The Authors conduct research at the Institute of Soil and Environmental Sciences at the University of Agriculture in Faisalabad, Pakistan.

Pakistan is basically an agricultural country and its economy is mainly agrarian. Agriculture is the biggest sector of the economy and contributes approximately 25% of GDP of the country (FAO, 2004). Pakistan, like many developing countries of the world, has been facing the problem of low agricultural productivity. One of the main reasons of low yields is the low fertilizer use efficiency, especially low nitrogen use efficiency (NUE) which is in no case more than 60% (Ahmad and Rashid, 2003). It means that about 40% of the applied nitrogen is lost. Consequently, it not only plays havoc with the sustainable crop production but also badly affects the environmental health. By estimating Pakistan’s monetary loss due to low NUE during 2004-05, we come to this terrifying conclusion that out of a total consumption of about 2.8 million tonnes of nitrogenous fertilizers (MINFAL, 2006), 1.2 million tones is lost to the environments, causing a loss in national wealth of about 186 million US dollars. Another aspect is the large crop yield gaps, brought about by this low NUE, which further elevates the national economic losses.  Hence, the gravity of the situation is direly demanding sound strategies to come up with workable solutions to improve the NUE, not only for improving agricultural productivity but also for cleaning the environments.

A wide range of products are being used to improve the growth and yield of crops. The use of plant growth regulators for this purpose has consistent success stories. The application of exogenous hormones has been found useful in increasing crop production (Fathima and Balasubramanian, 2006). Calcium carbide (CaC2) is a rich source of the nitrification inhibitor acetylene and the plant hormone ethylene. It releases acetylene gas upon its reaction with water (Yaseen et al., 2006) and increases the concentration of the plant hormone ethylene in soil air as a result of microbial reduction of acetylene (Bibik et al., 1995; Arshad and Frankenberger, 2002; Khalid et al., 2006a). Acetylene inhibits the activity of ammonia-oxidizing enzyme involved in the nitrification process. (Porter, 1992; Chen et al., 1994). This inhibits nitrification and denitrification processes and increases NUE (Sahrawat, 1989; Keerthisinghe et al., 1996; Thompson, 1996; Aulakh et al., 2001). Ethylene formed from biotic reduction of acetylene may accumulate in soil at physiologically active concentrations. Ethylene is a potent plant growth regulator involved in almost all the phases of plant growth and development, ranging from germination of seed to senescence of various organs (Muromstev et al., 1995; Arshad and Frankenberger, 2002).

The use of ethylene for the improvement of agricultural production has been limited because of its gaseous nature and therefore difficulty in its direct application to soil in the field. In the late 1960s, application of ethylene in liquid form under the trade name ‘Ethephone’ was a great breakthrough (Cooke and Randall, 1968; Sterry, 1969). At present, various ethylene releasing sources are available in market such as methionine, ethrel, CaC2, etc. (Bibik et al., 1995; Akhtar et al., 2005; Khalid et al., 2006a and Khalid et al., 2006b). The use of CaC2 has a dual benefit since it can act as a source of acetylene as well as ethylene gases, thereby improving growth and yield of crops.

CaC2 improves plant growth due to its double action, i.e. reducing N losses by acting as a nitrification inhibitor and by releasing a physiologically active concentration of ethylene to the soil. Moreover, partial inhibition of the nitrification process may release both nitrate and ammonium forms of nitrogen in the soil and this co-provision could have a synergistic effect on total nitrogen fluxes compared with the supply of either nitrate or ammonium forms alone (Lin et al., 2005).

Major crops such as wheat, rice, cotton and sugarcane occupy a central position in agricultural policies. So there is need to increase the production of these crops substantially by using non-conventional technologies. The use of CaC2 based formulation is an innovative approach to improve the growth and yield of crops.

The effectiveness of CaC2 in improving the growth, yield and NUE of different crops is demonstrated in the results of various studies conducted globally. Table 1 presents some results of improved NUE as a result of the application of encapsulated CaC2. According to one study, about 50% of the applied N was lost when urea was broadcasted into flooded water. Total N losses were significantly reduced when urea was either incorporated or deep placed in the presence of encapsulated CaC2 These losses were further reduced and the lowest loss (34%) was noted when urea was deep placed with encapsulated CaC2 (Keerthisinghe et al., 1996).

Table 1 · Nitrogen Use Efficiency (NUE)
Crop Nature of Study NUE (%) Reference
Wheat Pot > 60 Yaseen et al., 2006
Cotton Pot > 60 Yaseen et al., 2006
Rice Field 66 Keerthisinghe et al., 1996

In some other field and pot experiments, conducted to investigate the effect of CaC2 on growth and yield of rice, wheat and cotton crops, the encapsulated CaC2 released large amount of acetylene that was slowly reduced to ethylene. It was observed that CaC2 slowed down the release of nitrate from the applied urea, which might help in improving N use efficiency (Yaseen et al., 2004).

Research on the subject explained that the addition of wax coated CaC2 effectively inhibited the process of nitrification. The effectiveness of a urease inhibitor could not be judged solely from ammonical N concentrations in flooded water of a single treatment with the inhibitor. However, treatment with N-butylthiophosphoric triamide (NBPT) reduced ammonia losses and increased grain yield of rice up to 31% (Chaiwanakupt et al., 1996, Table 2.)

Table 2 · Benefits of using CaC2 in Improving Crop Growth and Yield
Crop Nature of Study Increase in Reference
Wheat Pot number of tillers by 46% Yaseen et al., 2006
root weight by 15%
straw yield by 33%
grain yield by 37%
Rice Field grain yield by 31% Chaiwanakupt et al., 1996
grain yield by 20% Yaseen et al., 2005
Cotton Pot number of bolls by 39% Yaseen et al., 2006
seed cotton yield by 31%
shoot weight by 28%

Some researchers showed that ethylene might play a role in rice grain quality. They sprayed AVG (aminoethoxyvinylglycine, an inhibitor of ethylene biosynthesis) or Ethephon from anthesis to grain ripeness. They found that ethylene production increased during flag leaf senescence and panicle ripening and starch concentration increased significantly in grains (Carbone and Vidal, 1997).

It was studied that ethylene increases the adventitious root formation in rice in early developmental stages which increases the nutrient uptake and growth of rice when applied in the form of Ethephon or 1-aminocyclopropane-1-carboxylic acid that is the direct natural precursor of acetylene and is converted to ethylene by endogenous 1-aminocyclopropane-1-carboxylic acid oxidase activity at optimal concentration without side effects (Lorbiecke and Sauter, 1999).

The research conducted at the Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad, revealed the usefulness of CaC2 application to wheat and cotton crops. In a pot experiment, the effect of time of application of encapsulated CaC2 was studied with and without NPK fertilizers on growth and yield of wheat. The study showed that plants responded positively to CaC2 application (60 kg ha-1). CaC2 treatment after one weak of germination was most effective in increasing number of tillers, length of spikes, number of spikelets, total biological yield, straw and grain yield of wheat (Mahmood et al., 2002). In two other pot trials conducted on wheat and cotton, it was found that encapsulated CaC2 applied at 30 mg kg−1 soil significantly increased the number of tillers (45.5%), root weight (14.9%), straw (32.8%) and grain yield (37.3%) of wheat over the fertilizer application alone (Table 2). In case of cotton, the number of bolls, root weight and seed cotton weight were also increased by 38.5%, 24.5% and 31.0%, respectively (Table 2), in response to the application of encapsulated CaC2 at 60 mg kg−1. However, increase in shoot weight was 28.1% due to encapsulated CaC2 applied at 30 mg kg−1. Moreover, application of encapsulated CaC2 resulted in greater NUE of >60% (Table 1) by both wheat and cotton crops than that observed at the same rates of N fertilizer alone (Yaseen et al., 2006).

In a field experiment involving rice crop, it was observed that the encapsulated CaC2 applied alone or along with chemical fertilizer significantly increased early emergence of panicle, number of tillers and paddy yield. Soil amended with encapsulated CaC2 resulted in 20% increase in paddy yield over NPK fertilizer alone (Table 2). Plant analysis also indicated that encapsulated CaC2 promoted N concentration and uptake by rice plant which is supported by the reduced oxidation of applied fertilizer ammonium to nitrate in the presence of encapsulated CaC2 (Yaseen et al., 2005).

These findings imply that CaC2 affects plant growth through hormonal action of ethylene as well as improved NUE; however, the latter factor might be a relatively more contributing. It is desirable that CaC2 is formulated for gradually slow release of acetylene and ethylene in soil air. Thus, CaC2 has significant effect on growth, yield and NUE of crops through effects of acetylene (as a nitrification inhibitor) and ethylene (plant hormone) (Yaseen et al., 2006). It is thus recommended in the literature that for improved growth, yield and NUE for rice, wheat and cotton CaC2 be applied @ 60 kg ha-1 by 5cm deep placement in the soil at the completion of germination followed by irrigation (Mahmood et al., 2002; Yaseen et al., 2006). However, extensive research is needed on the subject to clearly understand the mechanism of action of CaC2 in improving the growth, yield and nutrient use efficiency under various cropping systems and for setting up its recommended doses.

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