Energy input and output relationship in rice based cropping systems

: A field experiment was conducted in ICAR Research Complex at Goa, during 1999-2002 to study the energy input-output relationships of different rice based cropping systems with recycled manurial resources in a split-plot design with three replications. Among the cropping systems tried, rice-brinjal system received relatively higher energy input (23,135 MJ ha -1 ) that too from the non-renewable energy sources (14,909 MJ ha-1 ). However, the treatment could also yield substantially higher energy output (1,57,269 MJ ha -1 ). The use of recycled manures particularly paddy straw with mushroom spent substrate accounted for higher energy output although it recorded higher energy input (21,062 MJ ha -1 ). Rice-brinjal cropping system recorded better energy efficiency with additional input of energy in terms of irrigation which was mainly due to the higher productivity of the cropping system. In contrast, rice-sunnhemp and rice-fallow systems revealed lower energy input but ultimately their energy output was also lower.


Introduction
Farming uses energy intensive technologies for maximizing the productivity.The problems of energy consumption, shortage and environmental pollution have created an urge for processing organics for energy and plant nutrient recovery.Besides this, efficient utilization of renewable energy resources may play a key role in insulating Indian agriculture against any possible oil crisis in the world.The concept of integrated energy production and use management is based on research findings, that farm income is greatly enhanced by increased use of energy produced on the farm (Surendra singh et al. 1997).
For practice of integrated energy production and use-management, sources of energy available on the farm are to be used and it should form an integral part of the various activities and products of the farm.The integrated energy production and use management has been shown to be the most viable means of increasing agricultural production.Hence, convincing farmers and researchers to think in this direction is essential.Keeping these things in view, an attempt was made to assess the energy input-output relationships in a rice based cropping system involving residue recycling from the locally preferred crops suited to the agro-climatic conditions of Goa.

Material and methods
A field experiment was conducted during kharif-rabi seasons of 1999-2002 in ICAR Research Complex at Goa.The soil of the experimental site was sandy loam, acidic in reaction, having moderate levels of N (292 kg ha -1 ), P 2 O 5 (37.9 kg ha -1 ) and K 2 0 (264 kg ha -1 ).The experiment was conducted in a split-plot design with three replications.The recycled manurial resources from the rice based cropping systems and allied agroenterprises of dairy, poultry and mushroom production viz.farm yard manure, poultry manure, paddy straw with mushroom spent substrate (in 2:1 ratio) along with a control (no recycled manure) formed the main plot treatments.Rice (variety Jyothi) based cropping systems suited Brinjal fruits t ( fresh wt) 1.00 Mittal et al. (1985) to the location viz.rice-groundnut (variety DH-3-30), rice-cowpea (variety V-118), rice-brinjal (variety local Agassaim), rice-sunnhemp with rice-fallow system as control constituted the sub plot treatments.All the crop residues were incorporated in situ after the crop harvest.
The recommended dosage of fertilisers were applied both for rice and rice based crops.All the crops were grown under residual moisture except brinjal which was raised under protective irrigation as per the local practice.Practically no rain was received during the crop growth period of rice based crops.
The total energy for rice production system was calculated from the total material input energy plus their required operational energies in terms of renewable and non-renewable sources by each component in the system using equivalents of energy as per Mittal et al. (1985) and the same is presented in Table 1.The amount of output energy was calculated from the yield and biomass residues.Energy efficiency was worked out taking into account the input and output energy for each treatment adopting the method given by Dazhong and Pimental (1984) as Energy output (MJ ha -1 ) Energy efficiency = -----------Energy input (MJ ha -1 ) Specific energy of the system was calculated in terms of energy required to produce a kg of rice grain equivalent and expressed as MJ kg -1 Energy input (MJ ha -1 ) Specific energy = - --------------------------------Rice grain equivalent yield (kg ha -1 )

Energy input
The details of energy input for different cropping systems and recycled manures are presented in Table 2.The use of recycled manures particularly paddy straw with mushroom spent substrate (M 3 ) accounted for higher (21,062 MJ ha -1 ) energy input.However, the increased energy was from renewable sources (12,497 MJ ha -1 ), as paddy straw along with mushroom spent substrate was available within the system.The non-renewable energy input was nearly constant (8,565 MJ ha -1 ) with all the recycled manurial treatments due to application of recommended fertilizers.
Among the cropping systems tried, ricebrinjal system received relatively higher energy input (23,135 MJ ha -1 ) that too from nonrenewable energy sources (14,909 MJ ha -1 ).The requirement of non-renewable sources of energy for the system was relatively higher than the renewable energy as a result of higher energy involvement with irrigation, which ac-counted for nearly 60 per cent of the total energy requirement for the crop production as is also reported earlier by Jayanthi (1995).In contrast, rice-cowpea system was moderate in its energy input (14,898 MJ ha -1 ) without much dependence on non-renewable energy (8,036 MJ ha -1 ) sources.

Energy output
The mean energy output varjed among the recycled manures and cropping systems and the same is presented in Table 3.
Higher energy output (1,13,648 MJ ha -1 ) was recorded with recycling of paddy straw and mushroom spent substrate and was followed by recycled FYM (1,00,199 MJ ha -1 ).Energy output was the lowest when no manure was recycled (99,488 MJ ha -1 ).Recycling of paddy straw with mushroom spent substrate recorded 14.2 per cent higher energy output over no recycled manure treatment.
Among the cropping systems, rice-brinjal system recorded considerably higher energy output (1,57,269 MJ ha -1 ) and was followed by rice-cowpea system (97,562 MJ ha -1 ).Higher productivity of the crops in the sequence both in terms of economic and biomass yield with the application of recycled manures accounted for higher energy output.The lowest energy output (78,182 MJ ha -1 ) was recorded with ricefallow system.

Energy efficiency
Energy efficiency gives the energy produced per unit of energy invested.The mean energy efficiency was the highest with recycled poultry manure and when no recycled manure was applied (both 7.54) while recycling of paddy straw with mushroom spent substrate recorded lower energy efficiency (5.30).Rice-sunnhemp system was more efficient in energy conversion (energy efficiency 7.75) while rice alone was the next best in order (7.12) which was mainly due to the lesser energy input involved in contrast to the energy rich outputs.Rice-groundnut system recorded the least efficiency in terms of energy (5.66).However, rice-brinjal cropping system had better energy efficiency even with additional input of energy in terms of irrigation which was mainly due to the higher productivity of the cropping system.

Specific energy
Specific energy of a cropping system which indicates the energy required to produce a kg of rice grain equivalent, followed a trend similar to that of energy efficiency.The specific energy pooled over years revealed that the energy required to produce a kg of rice grain equivalent yield was the least with recycled poultry manure (2.1 MJ kg -1 ) and the highest with paddy straw with mushroom spent substrate (3.08 MJ kg -1 ) among the recycled manures.Rice-cowpea system was found to be the best with least energy requirement to produce a kg of rice grain equivalent yield (1.95 MJ kg -1 ).In contrast, cropping rice during kharif and fallow during rabi season recorded the highest specific energy (2.66 MJ to produce a kg of rice grain) among the cropping systems.

Table 1 .
Energy unit conversion equivalents for direct and indirect sources of energy

Table 2 .
Energy input in rice based cropping systems.

Table 3 .
Energy output in rice based cropping systems