Rice is generally grown under completely flooded condition and providing food for more than half of the world's population. Any changes in weather parameters might affect the rice productivity thereby impacting the food security of burgeoning population. So, the crop yield forecasting based on weather parameters will help farmers, policy makers and administrators to manage adversities. The present investigation examines the application of stepwise multiple linear regression (SMLR), artificial neural network (ANN) solely and in combination with principal components analysis (PCA) and penalised regression models (e.g. least absolute shrinkage and selection operator (LASSO) or elastic net (ENET)) for rice yield prediction using long-term weather data. The R and root mean square error (RMSE) of the models varied between 0.22-0.98 and 24.02-607.29 kg ha, respectively during calibration. During validation with independent dataset, the RMSE and normalised root mean square error (nRMSE) ranged between 21.35-981.89 kg ha and 0.98-36.7%, respectively. For evaluation of multiple models for multiple locations statistically, overall average ranks on the basis of R and RMSE of calibration; RMSE and nRMSE of validation were calculated and non-parametric Friedman test was applied to check the significant difference among the models. The ranking of the models revealed that LASSO (2.63) was the best performing model followed by ENET (3.07) while PCA-ANN (4.19) was the worst model which was found significant at p < 0.001. The reason behind good performance of LASSO and ENET is that these models prevent overfitting and reduce model complexity by penalising the magnitude of coefficients. Then, pairwise multiple comparison test was performed which indicated LASSO as the best model which was found similar to SMLR and ENET. So, for prediction of rice yield, these models can very well be utilised for west coast of India.

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A b s t r a c t. The study aims to elucidate the impact of organic inputs on strength and structural stability of aggregates in a sandy loam soil. Tensile strength, friability and water stability of aggregates, and the carbon contents in bulk soil and in large macro (>2 mm), small macro (0.25-2 mm), micro (0.053-0.25 mm) and silt+clay size (<0.053) aggregates were evaluated in soils from a long-term experiment with rice-wheat rotation at Modipuram, India, with different sources and amounts of organic C inputs as partial substitution of N fertilizer. Addition of organic substrates significantly improved soil organic C contents, but the type and source of inputs had different impacts. Tensile strength of aggregates decreased and friability increased through organic inputs, with a maximum effect under green gram residue (rice)-farmyard manure (wheat) substitution. Higher macroaggregates in the crop residue-and farmyard manure-treated soils resulted in a higher aggregate mean weight diameter, which also had higher soil organic C contents. The bulk soil organic C had a strong relation with the mean weight diameter of aggregates, but the soil organic C content in all aggregate fractions was not necessarily effective for aggregate stability. The soil organic C content in large macroaggregates (2-8 mm) had a significant positive effect on aggregate stability, although a reverse effect was observed for aggregates <0.25 mm. Partial substitution of nitrogen by organic substrates improved aggregate properties and the soil organic C content in bulk soil and aggregate fractions, although the relative effect varied with the source and amount of the organic inputs.K e y w o r d s: tensile strength, friability, aggregates, soil organic C, rice-wheat rotation mean weight diameter INTRODUCTIONSustainability of the rice-wheat system in the indo-gangetic plains (IGP) is crucial for meeting country food demand, and is also at the centre of global food security (Ladha et al., 2003a). This sustainability is arguably at stake, partly due to the staggering productivity, and partly due to degradation of soil quality (Ladha et al., 2003b). Continuous use of imbalanced fertilizers under intensive rice-wheat cultivation over the years had negative impacts on soil structure, organic carbon and nutrient supplying capacity of the soils (Bhandari et al., 2002;Regmi et al., 2002). Addition of organic inputs as a partial substitution of N has been one of viable options in restoring the soil quality and subsequently sustaining the system productivity.As the soil is collectively made of aggregates, the study at the single structural unit or aggregate has been useful to evaluate the soil response to management (Blanco-Canqui et al., 2005). Since the rice-wheat system involves two contrasting edaphic environments, the role of soil aggregation is of special importance. The mechanical properties of aggregates are clearly indicative of soil structural condition determining soil functions for plant growth. Tensile strength (TS), a fundamental property of ...

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