Influence of Time of Planting, Spacing, Seedling Number and Nitrogen Management Practices on Productivity, Profitability and Energetics of Rice ( Oryza sativa ) in Island Ecosystem

Field experiments were conducted during wet season of 2007 and 2008 at Central Agricultural Research Institute

Rice (Oryza sativa L.) is the most important staple food for nearly half of the world's population, which is grown under wide range of latitudes and altitudes with the challenges of climate change (Swaminathan, 2006).Rice is cultivated in 8,549 ha with annual production and productivity of 26,249 t and 2,200 kg/ ha, respectively, necessitating an import of about 27,188 t of rice from the Indian mainland (A&N Administration, 2009).Shrinking of land, water, labour, capital and energy are found to be a challenge in the Island ecosystem, thus requiring innovative research and technologies which can increase the unit area production of rice.Uphoff (2003) found that the SRI has ability to increase rice production by 26 % or more.Studies at many places of India revealed that planting single seedling resulted in 15 to 16 % higher yield than planting two to three seedlings/hill.Around 40 kg of seeds are used in conventional planting while rice can produce higher yield with single seedling (5 kg seeds/ha) or two seedlings (10 kg seeds/ha), thus saving grains of 30-35 kg/ha.Due to inadequate and imbalanced fertilizer application, farmers are not able to harness the full yield potential of rice in *Corresponding author email: damuvijayan@yahoo.co.in the islands.Practices of SRI such as number of seedling and spacing developed elsewhere would not be suitable for Island ecosystem as it receives annual average rainfall of 3070 mm with higher intensity.Hence, this study.

Materials and Methods
Field experiments were carried out during wet season of 2007 and 2008 at Field crops research farm, Bloomsdale of Central Agricultural Research Institute, Port Blair, Andaman & Nicobar Islands.The soil was clay loam in texture having slightly acidic pH (6.2), normal EC (0.2 dS/m), medium in organic carbon (0.6%), low in available Nitrogen (245 kg/ ha), medium in Phosphorus (11.2 kg/ha) and low in available Potassium (128 kg/ha).The experiment was laid out in split plot design having time of planting and spacing in main plot (Second fortnight of June with 20 x 20 cm (M1), Second fortnight of June with 25 x 25 cm (M2), Second fortnight of July with 20 x 20 cm ( M3) and Second fortnight of July with 25 x 25 cm (M4)) and seedling number (One (H1), Two (H2)) and nitrogen management (100 % of recommended dose of N through Gliricidia (N1), 100 % RDN through urea (N2), 50 % RDN through Gliricidia + 50 % RDN through urea (N3) and 75 % RDN through Gliricidia + 25 % RDN through urea (N4)) in subplot and replicated thrice.Seedlings of rice variety Bhavani were raised in MAT nursery and 15 day old seedlings were transplanted as per the treatments.Fertilizer dose of 90: 60: 40 kg N, P2O5 and K2O/ha was adopted and accordingly 100 % P2O5 and 50% K2O were applied as basal and remaining 50 % K2O was applied at panicle initiation stage through inorganic sources as per the treatment.The quantity of P2O5 supplied by Gliricidia (Gliricidia sepium) was estimated and the remaining quantity was supplemented with in organic sources.Gliricidia contained 2.9 % N, 0.5 % P2O5 and 2.8 % K2O on fresh weight basis.However, no addition of K from inorganic source was done as Gliricidia leaf incorporation met the entire K requirement.Nitrogen in the form of Urea, Phosphorus in the form of Single Super Phosphate and Potassium in the form of Muriate of potash was used as inorganic sources.Criss -cross conoweeding was carried out on 10, 25 and 40 DAT.Observations on growth and yield parameters were recorded as per standard procedure.Root volume was measured by displacement method and expressed in cubic centimeter (cc).Grains from individual net plot were sun dried, cleaned and weighed and yield was expressed at 14 per cent moisture basis while straw was sun dried for 4 days and weighed separately.Economic evaluation was done by calculating the gross return, net return, cost of cultivation and Net return per rupee invested (NRPRI) based on the prevalent market rate.Cultural energy (Mega Joules) used through various inputs in the cropping period was computed as described by Mittal et al. (1985) and the energy use efficiency (energy ratio) was worked out using the formula of Energy output divided by Energy input and Specific energy was 539 calculated in terms of energy required to produce a kilogram of economic yield and expressed in MJ/kg.All the observed data were subjected to statistical analysis as per the prescribed standard procedures for the similar kind of study.

Growth parameters
Time of planting, spacing, number of seedlings/ hill and N management practices did not significantly influence the plant height at flowering stage of rice in both the years.However, it had significant difference on number of tillers m-2, Leaf Area Index (LAI) and dry matter production (DMP) of rice (Table 1) .Early planting in June second fortnight with 20 x 20 cm spacing recorded 18.3, 6.9, and 7% higher tiller m-2 LAI and DMP respectively compared to delayed planting (July second fortnight with 20 x 20 cm spacing).The magnitude of increase was about 22.8, 10.2 and 9.3 % in terms of tiller m -2, LAI and DMP respectively compared to same time of planting with wider spacing (25 x 25 cm).Higher tillers in early planting with closer spacing can be attributed to long time of growth before flowering and optimum population.Nayak et al. (2003) also reported early planting exhibited maximum number of tillers in hybrid rice compared to delayed planting.Further closer spacing of 20 x 20 cm recorded the highest LAI compared to wider spacing of 25 x 25 cm.This might be due to more number of leaves which occupied the same land area and consequently trapped more light and CO2 resulting in higher photosynthesis and producing more dry matter.This corroborates with the findings of Salem (2006).DMP is the product of the influence of growth characters like plant height, number of tillers, LAI and efficiencies of the crop to capture available resources.Higher DMP in closer spacing may be because of higher Among the nitrogen management practices N2 (100 % RDN through urea) recorded higher tiller production (401/m2), LAI (5.27) and it was at par with N3 (50 % RDN through Gliricidia + 50 % RDN through urea) and N4 (75 % RDN through Gliricidia + 25 % RDN through urea).This might be attributed to slow and steady release of N by the gliricidia green leaf manure on its decomposition resulting in efficient utilization indicating that supplementing the inorganic fertilizer with organic source which improved the general soil environment, physico-chemical and biological conditions favouring the increased availability of macro and micro nutrients (Sengar et al., 2000) thereby helped in improving the rice growth.Similar finding was also reported by Singh et al. (2002).

Root characteristics
Root length, volume and weight were influenced by the time of planting, spacing and N management practices while number of seedlings/hill did not exert any pronounced effect.Maximum root length (25.9 cm), higher root volume (62.3cc) and more dry weight (26.5 g/hill) was recorded under June second fortnight planting with 20 x 20 cm spacing followed by July second fortnight planting with 20 x 20 cm (Fig. 1).In the present findings, it was observed that Fig. 1.Influence of management practices on root characteristics of rice at flowering stage early planting in June second fortnight with 20 x 20 cm recorded longer roots since higher plant density increases the length of roots due to competition for uptake of water and nutrients from the soil.Further, the better root characteristics may be attributed due to the effect of cono weeding which resulted in formation of more number of roots as well pruning of some of the upper roots and thus encouraged deeper root growth thereby increasing the root length and volume (Uphoff, 2002).Among the nitrogen management practices, lengthier roots (24.3 cm) with higher volume (59.1 cc) and dry weight (25.2 g) were recorded with N2 (100 % RDN through urea) but, it was at par with N3 (50 % RDN through Gliricidia + 50 % RDN through urea).This can be due to the large amount of N supplied to leaves from roots which enhanced the photosynthesis and secured the supply of carbohydrates to roots (Osaki et al., 1997).The higher root dry weight may be due to cumulative effect of lengthier roots and higher root volume due to number of roots and root thickness.

Yield attributes
The yield attributes viz, panicles/m2, panicle length and filled grains/panicle was significantly influenced by the time of planting, spacing and N management practices while number of seedlings/ hill did not show much variations on the yield attributes (Table 2).
Early planting in June second fortnight with 20 x 20 cm spacing recorded 9.1 % higher panicles/m2, lengthier panicle with higher number of filled grains/ panicle (108) compared to the same time of planting in 25 x 25 cm.The number of panicles/ m2 was higher at increased plant density and decreased with wider spacing.This may be due to greater plant population per unit area rather than more tillers/ plant.Similar results were earlier reported by Choudhury et al. (2007).Among the nitrogen management practices, N2 (100 % RDN through urea) recorded the higher number of panicles ( 218) and filled grains/panicle but the same was at par with N3 (50 % RDN through Gliricidia + 50 % RDN through urea) and N4 (75 % RDN through Gliricidia + 25 % RDN through urea).This may be due to the conjunctive use of inorganic fertilizer with organic source which inturn improved the general soil environment, physicochemical and biological conditions.Similar findings were earlier reported by Natarajan et al. (2005).

Yield
Early planting in June second fortnight with 20 x 20 cm (25 hills/m2) recorded significantly higher grain and straw yield in both the years (Table 3 & 3.

1).
The increase in grain yield was 461 kg/ha in 2007 and 470 kg/ha in 2008 and 30 % and 26 % higher straw yield in the corresponding years as compared to the same time of planting with wider spacing of 25 x 25 cm (16 hills/m2).At the same time one month delay in planting (July second fortnight) accounted 357 and 368 kg/ha reduction in yield with same density of population.This can be attributed to better growth and yield components due to efficient utilization of resources which in turn improved the yield attributes and thereby increased the yield.It clearly indicates that early planting enabled the plants to have longer time for growth before flowering and had potential for higher source capacity from which more dry matter could be produced for storage in the economic organs.Further due to more number of panicles/m2 produced in the early planting with closer spacing must have contributed to higher grain yield.Similarly Gill et al. (2006)    Application of 100 % RDN through urea recorded the highest grain (4,591 and 4,340 kg/ha) and straw yield (6,015 and 5,524 kg/ha) in 2007 and 2008 but it was on par with 50 % RDN through Gliricidia + 50 % RDN through urea and 75 % RDN through Gliricidia + 25 % RDN through urea.The interaction effect indicates that early planting in June second fortnight with closer spacing responded well for the integrated N management practices as compared to RDN through urea alone and accordingly higher grain yield (4,923 kg/ha) was recorded with the application of 50 % RDN through Gliricidia + 50 % RDN through urea and it was at par with 75 % RDN through Gliricidia + 25 % RDN through urea.Gliricidia green leaf manuring might have not only attributed steady and uninterrupted supply of nutrients throughout the crop growth period, but also increased the fertilizer use efficiency and improved the physical, chemical and biological properties of soil thereby paving the way for better utilization of nutrients resulting in similar trend in yield as compared to RDN only through urea.Moreover, higher yield under SRI can also be attributed to conoweeding as it minimizes the weeds besides increasing the soil aeration and root pruning.

Economics
The economic analysis revealed marked variation in cost of cultivation due to spacing (Table 4) .Higher cost was incurred under the closer spacing (20x 20 cm) which reduced correspondingly with further widening in plant spacing (25 x 25 cm).This may be due to higher labour cost involved for transplanting and harvesting.Early planting in second fortnight of June at 20 x 20 cm recorded higher net returns (Rs.31,768/ha) and net return per rupee invested (1.47).Two seedlings/hill recorded marginally higher net return (564/ha) over single seedling/ hill.Among the N management practices, though the net return was marginally higher (Rs.327/ha) with the application of 100 % RDN through urea compared to application of 50 % RDN through Gliricidia + 50 % RDN Urea (N3), the later resulted in higher net return per rupee invested (1.40) which indicates the positive effect of organics and fertilizer nitrogen on the grain yield.

Energetics
Early planting in second fortnight of June at closer spacing of (20 x 20 cm) recorded significantly higher output energy (1,509 x 103 MJ/ha) followed by planting in second fortnight of July with 20 x 20 cm (Table 5).Among the N management practices, though N2 (100 % RDN through urea) recorded the higher output energy (1,377 x 103 MJ/ha), it was at par with N3 (50 % RDN through Gliricidia + 50 % 543 RDN through urea) and N4 (75 % RDN through Gliricidia + 25 % RDN through urea).Energy output depends on grain and straw yield.In the present investigation, the higher output energy recorded in early planting in second fortnight of June at closer spacing of 20 x 20 cm and application of 100 % RDN through urea (N2) and N3 (50 % RDN through Gliricidia + 50 % RDN through urea) confirms that it was mainly due to higher grain and straw yield obtained in the respective treatments.
In contrast, specific energy and energy ratio was not significantly influenced by time of planting, spacing and number of seedlings/hill, but it was influenced by N management practices.Specific energy, a measure of energy required to produce one kilogram of paddy was higher (2.89 MJ/Kg) with application of 100 % RDN through Gliricidia (N1) was mainly due to lesser grain yield coupled with more energy intake in terms of inputs.Similar findings were reported earlier by Ravisankar et al. (2008).Similarly the energy ratio indicates the ratio in terms of energy between output and input, which was higher under N 3 (50 % RDN through Gliricidia + 50 % RDN through urea).This might be due to the combined effect of reduced energy consumption and more output in terms of grain and straw yield.This is in agreement with the findings of Balakrishnan et al. (2010).

Table 1 . Influence of management practices on growth parameters of rice at flowering stage
Number of seedlings/hill did not show much variation in the growth parameters and it clearly indicates that use of extra seedling in a hill do not provide any extra benefit.
RDN= Recommended dose of Nitrogen; Interaction not significant plant population as compared to the wider spacing.

Table 2 . Influence of management practices on yield components of rice
Latif et al. (2009)04)transplanting in July compared to June resulted in sharp reduction in grain yield due to reduction in favourable growing period.Further wider spacing may increase yield per plant but may often lead to a decrease in grain yield per unit area due to less plant population.This is true in the present findings.Closer spacing gave higher yield in comparison with wider spacing.Karmakar et al. (2004)reported that closer spacing gave higher yield in comparison with wider spacing.Number of seedlings hill-1 had no significant effect on yield.Though planting two seedlings/hill recorded numerically higher grain and straw yield but it was in close comparison with one seedling/ hill.Similar findings were reported byLatif et al. (2009).