December 18, 2006	Monday	Ziqa'ad 26, 1427

PAKISTAN has been facing the problem of low agricultural productivity. One of the main reasons of low yields is the inefficient use of fertiliser especially nitrogen use efficiency (NUE) which is in no case more than 60 per cent.

It means that about 40pc of the applied nitrogen is lost mainly through its conversion to nitrate form by microorganisms, the process being nitrification. This nitrate form is water soluble and lost either through leaching to underground water and pollutes it or through denitrifying in gaseous form and contaminates the atmosphere, the process being volatilisation.

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 conclusion that out of total consumption of about 2.8 million tons of nitrogenous fertilisers, we have lost about 1.2 million tons to the environments thus inflicting a loss of $186 million.

Another aspect is the large yield gaps of the crops brought about by this low NUE which further increases the monetary losses. Hence, the situation is demanding urgent steps 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 application of exogenous hormones has been found useful in increasing crop production. Calcium carbide is a rich source of the nitrification inhibitor acetylene and the plant hormone ethylene. It is known to release acetylene gas upon its reaction with water. It has recently been reported to increase the concentration of the plant hormone ethylene in soil air as a result of microbial reduction of acetylene. Acetylene inhibits the activity of ammonia-oxidizing enzyme involved in the nitrification process.

This inhibits nitrification and de-nitrification processes and increases N fertiliser use efficiency. 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.

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. At present, various ethylene releasing sources are available in the market such as methionine, ethrel, calcium carbide, etc. The use of calcium carbide 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.

Calcium carbide 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.

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 calcium carbide based formulation is an innovative approach to improve the growth and yield of these crops.

The effectiveness of calcium carbide is demonstrated in the results of various studies conducted globally. According to one study, about 50 per cent 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 calcium carbide. These losses were further reduced and lowest loss was noted when urea was deep placed with encapsulated calcium carbide.

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

Research on the subject explained that the addition of wax coated calcium carbide effectively inhibits the process of nitrification. The effectiveness of a urea 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) reduces ammonia losses and increases grain yield of rice up to 31 per cent.

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.

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.

The research conducted at the Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad, revealed the usefulness of calcium carbide application to wheat and cotton crops. In a pot experiment, the effect of time of application of encapsulated calcium carbide was studied with and without NPK fertilisers on growth and yield of wheat. The study showed that plants responded positively to calcium carbide application (60 kg ha-1). Calcium carbide 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. In two other pot trials conducted on wheat and cotton, it was found that encapsulated calcium carbide applied at 30 mg kg-1 soil significantly increased the number of tillers (45.5pc), root weight (14.9pc), straw (32.8pc) and grain yield (37.3pc) of wheat over the fertiliser application alone.

In case of cotton, the number of bolls, root and seed cotton weight were also increased by 38.5pc, 24.5pc and 31.0pc, respectively, in response to the application of encapsulated calcium carbide at 60 mg kg-1. However, increase in shoot weight was 28.1pc due to encapsulated calcium carbide applied at 30 mg kg-1. Moreover, application of encapsulated calcium carbide resulted in greater NUE (>60%) by both wheat and cotton crops than that observed at the same rates of N fertiliser alone.

In a field experiment involving rice crop, it was observed that the encapsulated calcium carbide applied alone or along with chemical fertiliser significantly increased early emergence of panicle, number of tillers and paddy yield. Soil amended with encapsulated calcium carbide resulted in 20pc increase in paddy yield over NPK fertiliser alone.

Plant analysis also indicated that encapsulated calcium carbide promoted N concentration and uptake by rice plant which is supported by the reduced oxidation of applied fertiliser ammonium to nitrate in the presence of encapsulated calcium carbide.

These findings imply that calcium carbide 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 calcium carbide is formulated for gradually slow release of acetylene and ethylene in soil air. Thus, calcium carbide has significant effect on growth, yield and NUE of crops through effects of acetylene (as a nitrification inhibitor) and ethylene (plant hormone).