Numerous spectral vegetation indices have been developed to characterize vegetation canopies. These indices will easily predict or quantify the plant stress at earlier with help of remote sensing techniques. Field experiments were conducted at the Tamil Nadu Agricultural University, Coimbatore, Tamilnadu, India during rabi 2013 with maize crop. To ensure the stressed environment, the crop was subjected to two irrigation levels (CPE: 0.80, 0.50) and five staggered nitrogen levels (0, 50, 75, 100 and 125% of RDN. The experiment was laid out in FRBD with three replication. Measured spectral reflectance curve of maize exhibited a broad low intensity peak centered in the green region at 550 nm and a sharp rise starting at about 685 nm to a plateau in the vicinity of 762 nm under unstressed environment created with irrigation at 0.80 IW/CPE ratio and fertilizer application at 100% RDN. Significant differences in reflectance were established for nitrogen and water stress at green and NIR region. The spectral indices viz., NDVI, GNDVI, RVI, LCI, IR-RED and SR recorded higher value on unstressed maize crop and plants under stress caused reduction in value of these indices at 60 and 90 DAS. All the spectral vegetation indices correlated positively with LAI and SPAD values with a correlation coefficient above 0.80 at both stages. These results highly support the ability of spectral vegetation indices to quantify the combined effect of nitrogen and water stress on maize too earlier through remote sensing.

Maize (Zea mays L.) is one of the most versatile cereal crops having wider adaptability under varied agro-climatic conditions. Nitrogen and water are the main abiotic factors that limit the yield of maize worldwide. The formulation of nitrogen and water management practices is needed to ensure food productivity for the increasing world population and to address the growing concerns regarding the adverse environmental impacts of agricultural activities. Hence, considering the overall performance in terms of growth, yield and economic returns, it is concluded that with 250 kg N ha -1 and irrigation at 0.80 IW/CPE ratio can be recommended under irrigated condition to get higher productivity and benefit cost ratio of maize. In future need to studies that distinguish between biotic and abiotic stress in maize involving spectral remote sensing for vital information required both for the quantification of consequences on production and for taking action for their mitigation.

Field experiments were conducted at the Tamil Nadu Agricultural University, Coimbatore, Tamilnadu, India during rabi (winter) season of 2013-14 with maize crop (TNAU maize hybrid Co 6). To ensure the stressed environment, the crop was subjected to two irrigation levels (IW/CPE: 0.80 and 0.50) and five staggered nitrogen levels (0, 50, 75, 100 and 125 % of recommended dose of nitrogen (RDN).The experiment was laid out in factorial randomized blocks design RBD (Factorial) with three replications. Hyper spectral observations were made with spectroradiometer GER 1500 at 60 and 90 days after sowing (DAS). Measured spectral reflectance curve of maize exhibited a broad low intensity peak centered in the green region at 550 nm and a sharp rise starting at about 675 nm to a plateau in the vicinity of 762 nm under unstressed environment created with irrigation at 0.80 IW/CPE ratio and fertilizer application at 100 % RDN. Significant differences in reflectance were established for nitrogen and water stress at green and NIR region. The results of Classification tree analysis revealed that nitrogen and water stress can be assessed and differentiated using reflectance data when transformed into spectral vegetation indices viz., NDVI, GNDVI, RVI, LCI, IR-RED and SR. Further the Classification tree algorithm coulddetermine that NDVI was the most effective index to assess the combined effect of nitrogen and water stress in maize crop.

The effect of seaweed formulations on the growth and development, quality and yield response of sugarcane variety Co 86032 was evaluated by conducting field experiment. The results of the study indicated that the foliar application of seaweed formulations with different concentrations significantly improved the plant height, LAI, SPAD value and total dry matter production (TDMP), yield and yield components compared to control plants. Among the seaweed extract formulations tested, LBS 6 @ one ml/L recorded significantly higher plant growth parameters, yield attributes and cane yield (161 t. ha-1) compared to other treatments studied. It was found that sugarcane cane yield was increased significantly by 22.2 % over control. This treatment also recorded higher economic returns (Rs. 2,38,300. ha-1) and benefit cost ratio (2.08).

Field experiment was conducted at Agricultural College and Research Institute, Madurai during Rabi 2010-2011 to study the performance of new herbicides on productivity and profitability of aerobic rice with twelve treatments in randomized block design. In this study, post-emergence mixture of fenoxaprop + (chlorimuron + metsulfuron) on 30 DAS provided a broad spectrum of weed control by significantly reducing weed density and dry weight at 60 DAS and resulted in significantly higher weed control efficiency. Post-emergence mixture of fenoxaprop + ethoxysulfuron on 30 DAS recorded significantly higher grain yield and straw yield. The economic evaluation of results indicated that post emergence mixture of fenoxaprop + ethoxysulfuron on 30 DAS registered higher gross return (Rs. 50915 ha -1 ), net return (Rs. 28281 ha -1 ) and B:C ratio (2.25).

Field experiments were conducted at the Tamil Nadu Agricultural University, Coimbatore, Tamilnadu, India during kharif and rabi season of 2014 with maize crop (TNAU maize hybrid Co 6). To ensure the stressed environment, the crop was subjected to two irrigation levels (IW/CPE: 0.80 and 0.50) and five staggered nitrogen levels (0, 50, 75, 100 and 125 per cent of recommended dose of nitrogen (RDN). The experiment was laid out in randomized blocks design RBD (Factorial) with three replications. A higher value of spectral vegetation indices viz., NDVI, GNDVI, RVI, LCI, IR-RED and SR were recorded with irrigation at IW/CPE ratio 0.80 either with 100 or 125 per cent RDN (unstressed) applied to maize crop. Maize under stressed environment recorded reduced values of spectral vegetation indices when the crop was irrigated at 0.50 IW/CPE ratio with no nitrogen. All the spectral vegetation indices expressedpositive correlation (highly significant at 1 per cent probability level) with crop parameters. The overall best fit was linear with a regression coefficient between vegetation indices (GNDVI, NDVI) and with crop parameters, and actual grain yield and predicted yield (0.81 to 0.85) of maize. The ability of spectral vegetation indices to quantify the combined effect of nitrogen and water stress on maize too early through remote sensing paves the way for large scale application of satellite remote sensing.

Field experiment was conducted at Agricultural College and Research Institute, Madurai during Rabi 2010-2011 to study the effect weed management on growth and yield attributes and yield of aerobic rice. Growth parameters of rice such as plant height, LAI, number of tillers m-2, SPAD value (Chlorophyll) of leaves and DMP of rice were enhanced by post-emergence mixture of fenoxaprop + ethoxysulfuron on 30 DAS (T9). This mixture of herbicides (T9) also increased the yield attributes such as number of panicles m-2, number of filled grains panicle-1 and test grain weight which in turn resulted in higher grain yield.

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