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A field experiment with wheat was conducted with four different nitrogen and four different water stress levels, and hyperspectral reflectances in the 350-2500 nm range were recorded at six crop phenostages for two years (2009-2010 and 2010-2011). Thirty-two hyperspectral indices were determined using the first-year reflectance data. Plant nitrogen (N) status, characterized by leaf nitrogen content (LNC) and plant nitrogen accumulation (PNA), showed the highest R 2 with the spectral indices at the booting stage. The best five predictive equations for LNC were based on the green normalized difference vegetation index (GNDVI), normalized difference chlorophyll index (NDCI), normalized difference 705 (ND 705 ) index, ratio index-1dB (RI-1dB) and Vogelman index a (VOGa). Their validation using the second-year data showed high R 2 (>0.80) and ratio of performance to deviation (RPD; >2.25) and low root mean square error (RMSE; <0.24) and relative error (<10%). For PNA, five predictive equations with simple ratio pigment index (SRPI), photochemical reflectance index (PRI), modified simple ratio 705 (mSR 705 ), modified normalized difference 705 (mND 705 ) and normalized pigment chlorophyll index (NPCI) as predicting indices yielded the best relations with high R 2 > 0.80. The corresponding RMSE and RE of these ranged from 1.39 to 1.13 and from 24.5% to 33.3%, respectively. Although the predicted values show good agreement with the observed values, the prediction of LNC is more accurate than PNA, as indicated by higher RMSE and very high RE for the latter. Hence, the plant nitrogen stress of wheat can be accurately assessed through the prediction of LNC based on the five identified reflectance indices at the booting stage.

Field experiments were conducted to study the effect of irrigation and nitrogen levels on radiation use efficiency (RUE), radiation extinction coefficient (κ) and temporal variation of leaf area index (LAI) and fraction intercepted photosynthetically active radiation (fIPAR). The LAI of wheat increased with increase in irrigation and nitrogen levels. The fIPAR also followed trend similar to LAI. The LAI and fIPAR showed logarithmic relationship with R2 value of 0.92 and 0.93 for the years 2013–2014 and 2014–2015, respectively. The κ value varied between 0.41 and 0.78 and was significantly affected by nitrogen levels but was not influenced by irrigation levels. The grain and above ground biomass (AGB) yields of wheat were not affected significantly by irrigation levels. However, application of 160 kg N ha−1 (N160) registered higher grain (12–33%) and AGB (22–25%) yeilds as compared to that with application of 40 kg N ha−1 (N40). Similar to AGB, the total intercepted photosynthetically active radiation (TIPAR) was not affected by irrigation levels but N160 treatment registered 9–20% higher TIPAR compared to N40 treatment. The linear relationship between TIPAR and AGB revealed that 83–86% variation in AGB yield of wheat can be explained by TIfIPAR. The RUE of wheat under three irrigations (I3) was 6 and 18% higher (P < 0.05) than the five (I5) and two (I2) irrigation treatments, respectively for the year 2013–2014. However, there was no significant effect of irrigation on RUE of wheat in the year 2014–2015. N160 treatment registered 5–13% higher RUE than the N40 treatment. Thus wheat may be grown with three irrigations (CRI, flowering and grain filling) and 160 kg N ha−1 for higher RUE without significant reduction in AGB of wheat compared to five irrigation levels in semi-arid location of Delhi region.

Water and nutrient deficiency are two major constraints that drastically affect rapeseed and mustard production under semi-arid regions of North-Western India. To cope with this problem, a study was undertaken to optimize irrigation, nitrogen and sulphur levels for productivity and quality of Ethiopian mustard(Brassica carinata).Field experiments were conducted during winter seasons of 2004-05 and 2005-06 at the Water Technology Centre (WTC), Indian Council of Agricultural Research (ICAR) -Indian Agricultural Research Institute (IARI), New Delhi, India. Irrigation, nitrogen and sulphur levels significantly (P<0.05) affected plant height, LAI, siliqua weight, seeds/siliqua, test weight, seed and biomass yield of Ethiopian mustard. Application of three irrigations (seedling, 50% flowering and pod development stage) to Ethiopian mustard increased seed yield by 27-28% compared to one irrigation (seedling stage). Nitrogen @ 90 kg ha -1 produced 49-54 % higher seed yield of Ethiopian mustard compared to no application. Similarly, sulphur application @ 40 kg ha -1 increased seed yield by 33-34 % compared to no application of sulphur. The oil content of Ethiopian mustard was significantly (P<0.05) affected by nitrogen and sulphur levels. Among the three treatments, irrigation treatment only significantly affected evapotranspiration of the studied crop. From the above study, it is suggested that application of 3 irrigations with 90 kg N ha -1 and 40 kg S ha -1 may be practiced for achieving higher seed yield, quality and water use efficiency of Ethiopian mustard in the semi-arid environment of Northern part of India.

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