Influence of Weeds as Nutrient Source on Paddy Yield, Residual Soil Properties and Economics

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The soil of each plot were irrigated to field capacity after the incorporation of Parthenium and Chromolaena as green manure and their compost and kept as such for 20 days before transplanting of paddy so as to give sufficient time for their decomposition.After 20 th day the soil of each plot was dug and again mixed thoroughly.The recommended dose of fertilizer (100:50:50) was applied through urea, DAP, muriate of potash.The N was applied in two splits while P and K were applied at transplanting.At maturity, the grain and straw were separated and their dry weights were recorded.After the harvesting of the crop, the residual properties of the soils were estimated using standard procedures.The cost benefit ratio was calculated.

Grain and straw yield
In the present experiment, treatment T10: RDF + CC2 improved the grain yield better than organic sources (Table 1).The yield increase is due to conjunctive application of RDF and organic manures which could be due to the increased availability of nitrogen, phosphorus and potassium in soil and the resultant in increase in the number of tillers, panicle and other growth attributes as a result of better uptake of nutrients from soil as reported by many workers (Basavaraja, 2001;Kenchaiah, 1997;Paraye, 2002;and Meelu and Morris, 1988).
Straw yield also followed the similar trend as that of grain yield.Increase in straw yield was due to the influence of fertilizer with different levels of organic manures, which was mainly due to more number of tillers and plant height.The results are in close conformity with the findings of other workers with the use of green manures in rice production (Meelu andMorris, 1988 andRamtete et al., 1998).

Effect on soil properties
Application of recommended dose of fertilizers in combination with organic manures had favourable effect on soil chemical properties.The soil pH differed significantly in soil after harvest due to treatments.The incorporation of organic manures helps in stabilizing pH and resists fluctuation in pH due to management practices.The EC values differed significantly among treatments, which may be due to varying degrees of soluble salts in compost (Table 2).
There was a significant increase in the OC content of the soil and was due to different levels of organic manures application.The OC content of soil changed in accordance with chemical composition of the organic manures.Organic carbon content of the soil was higher in the treatment which received both RDF + Chromolaena compost @ 7.5 t ha -1 (T10: RDF + CC2).Increased organic carbon status with application of eupatorium was also reported by Manjappa (1999) and Vinod Kumar et al. (1998).Application of higher amount of green biomass produced higher values of organic carbon, available P2O5 and K2O in soil compared to lower level of its application (Bouldin, 1988).
There was a significant increase in the available N, P2O5 and K2O content of the post harvest soil in treatments T10: RDF + Chromolaena compost @ 7.5 t/ha, T4: RDF + Parthenium green manure @ 7.5 t/ha, T5: RDF + Parthenium compost @ 5.0 t/ha and T6: RDF + Parthenium compost @ 7.5 t/ha.This might be due to the mineralization of N from the compost during decomposition and also the application of recommended dose of fertilizer.This is in agreement with the findings of Manjappa (1999).The increased available P2O5 in post harvest soil was due to the release of P from compost enriched with rock phosphate.Similar results were reported by Budhar et al. (1990), Chaphale et al. (2000) and Sharma and Verma (2000).The increase in available K2O with conjunctive use of RDF + organic manures was reported by Bouldin (1988).Higher availability of K2O might be due to less involvement in organic fractions of green manure which helped for its faster release during decomposition.
There was significant differences between treatments with respect to exchangeable Ca and Mg content of the post harvest soil.The available S content of the soil recorded higher values in T10: RDF + Chromolaena compost @ 7.5 t/ha, T9: RDF + Chromolaena compost @ 5.0 t/ha, T5: RDF + Parthenium compost @ 5.0 t/ha and T6: RDF + Parthenium compost @ 7.5 t/ha treatments over initial S content of soil.The increase in available S in compost treatment could be attributed to the  Tester and Parr, (1983).
DTPA extractable micronutrients of the post harvest soil showed an increase in all the treatments.The organic manures which are good reservoir of micronutrients and it is observed that soil which receives continuous application of organic manures seldom show an increase in micronutrient status.

Economics
The cost of cultivation was higher with the use of recommended dose of fertilizer in combination with various levels of organic manures when compared to the use of only organic manures (Table 3).
Analysis of economics reveled that the net return and benefit cost ratio obtained with the application of recommended dose of fertilizer in combination with Chromolaena compost @ 7.5 t/ha (T10: RDF + CC2) (Rs.39, 957 and 2.29) and recommended dose of fertilizer in combination with Parthenium compost @ 7.5 t/ha (T6: RDF + PC2) (Rs.38.274 and 2.22), respectively were similar.This suggested that both Parthenium and Chromolaena can be used advantageously as a source of nutrients for the soil.T7: RDF + CG1 and T8: RDF + CG2 reveled B:C ratio of 4.31 and 4.28 respectively where as T10: RDF + CC2 records 2.29.This suggests that the application of Chromolaena as green manure to paddy field records better income compared to their compost, preparation of compost was not economical but it gives better yield.Mehla and Panwar (2000), obtained higher gross return (Rs.45,425 ha -1 ) with conjunctive use of FYM and nitrogen in rice as compared to FYM alone (Rs.36, 225 ha -1 ) Combined application of organics and fertilizers sustained the grain yield at higher levels due to improvement in physical, chemical and biological properties of soil (Yadvinder Singh et al., 1991).The available weeds such as Parthenium and Chromolaena in agricultural field we can use it as green manures and also compost can be made using the weeds.Weeds and their composts contain good source of nutrients.Therefore, the combined use of recommended dose of fertilizer with Chromolaena and Parthenium as green manure and also their compost give better yield.