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.

A field investigation was carried out in farmer's field at Pudhupalayam, TNAU, Coimbatore, during 2015, to improve the productivity of groundnut variety TMV 13 under drip and micro sprinkler fertigation system. The experiment was laid out in randomized block design (RBD) with three replications comprising of 11 treatments. Results indicated that maximum pod yield (3495 kg ha -1 ), haulm yield (6452 kg ha -1 ), harvest index (0.351) and shelling per cent (73.95 per cent) were obtained with drip irrigation at 100% PE with fertigation at 100% RDF as WSF (T 1 ). The water saving achieved under drip irrigation was 40.08% and 55.06% at 100% and 75% PE, respectively, whereas, under micro-sprinkler, it was 25.10% and 43.83% at 100% and 75% PE, respectively over surface irrigation. Higher WUE of 19.28 kg/ha-mm recorded under drip irrigation at 75% PE with fertigation at 100% RDF as WSF (T 2 ) followed by drip irrigation at 100% PE with fertigation at 100% RDF as WSF (T 1 : 15.88 kg/ha-mm). Highest NUE (23.30 kg kg -1 NPK ha -1 ) was recorded in drip irrigation at 100% PE with fertigation at 100% RDF as WSF (T 1 ). Drip irrigation at 100% PE with fertigation at 100% RDF as WSF (T 1 ) recorded higher gross return (Rs. 254353 ha -1 ) and net return (Rs.134712 ha -1 ). Whereas, the benefit cost ratio was highest in micro sprinkler at 100% PE with fertigation at 100% RDF as WSF (T 6 : 2.41). The margin benefit cost ratio (MBCR) was recorded highest under micro sprinkler at 100% PE with fertigation at 100% RDF as WSF (T 6 : 2.53) as compared to all other treatments.

A study was conducted to determine the effect of low cost drip tape irrigation system on yield and economics of sweet corn in comparison to conventional inline drip irrigation and surface irrigation systems during 2013-14 at Coimbatore, India. The treatment comprises of two drip irrigation systems with three irrigation levels viz., 75, 100 and 125% of pan evaporation (PE) from Class A Pan evaporimeter. Plant height, fresh cob length, girth, number of kernels per cob and single fresh cob weight and yield were higher at 125% PE in conventional in line drip irrigation system and it was statistically at par with drip irrigation at 125% PE in low cost drip tape irrigation system. Water saving was 36, 49 and 62% at 125, 100 and 75% PE, respectively under conventional in line drip irrigation system and drip tape irrigation system as against the surface irrigation. The cost of low cost drip tape system was 68% lower than the conventional inline drip system. The results of the research indicated that based on net income, B:C ratio and GM/TMV ratio, adoption of low cost drip tape irrigation system at 125% PE was found to be best for small and marginal farmers with substantial yield and income compared to conventional inline drip system.

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