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Large quantities of rice husk ash (RHA), bagasse ash (BA) and coal fly ash (FA) are available in many Asian countries as waste materials, which create a serious disposal problem. Recycling of these ashes on agricultural land can help to improve physical and chemical fertility of soil. The present field experiment was conducted for three and half years to explore the possibilities to utilize these waste materials as soil amendments to improve productivity of rice–wheat system (RWS). The treatments consisted of application of RHA and BA at 10 Mg ha−1 to either wheat or to rice or to both wheat and rice and 20 Mg ha−1 to rice alone. The rates used for FA were 15 and 30 Mg ha−1. Addition of RHA and BA significantly increased the grain yield of wheat and rice but FA caused small increases in crop yields. Direct application of RHA and BA to wheat was significantly superior than their application to rice in the RWS. Direct application of RHA and BA to wheat resulted in 25 and 24% increase in mean grain yield of wheat and 10 and 11% increase in subsequent rice crop, respectively. However, direct application to rice resulted in 8 and 11% yield increase in rice and 10 and 14% increase in subsequent wheat for RHA and BA, respectively. Application of RHA and BA at 20 Mg ha−1 to rice resulted in lower RWS productivity than that applied at 10 Mg ha−1 to wheat. There was no significant effect of these ashes on heavy metal contents in grain and straw of the 7th crop of wheat. Application of three types of ashes generally resulted in positive P balance in RWS, however, K balance remained negative. These results suggest that RHA and BA can be recycled successfully in rice–wheat system to improve its productivity with no adverse effect on soil health.

Over and untimely application of fertilizer nitrogen (N) are the major constrains in improving fertilizer N recovery efficiency in irrigated wheat ( Triticum aestivum L.). Large field to field and seasonal variability further lower fertilizer N recovery efficiency when broad based blanket recommendations are followed. Six field experiments were conducted during 2005 to 2009 at different locations to establish threshold leaf colour greenness to guide in-season need-based fertilizer N topdressings in wheat. Colour of the first top fully exposed leaf as measured by comparison with different shades of green colour on a leaf colour chart (LCC) and wheat grain yield were significantly correlated. The Cate-Nelson plot of leaf greenness expressed as LCC values against relative grain yield of 0.91 indicated that leaf greenness between LCC shade 4 and 5 may guide crop demand driven N applications in wheat. A series of experiments with progressive refinement in treatments were conducted to develop adequate need-based N management strategy using a single threshold LCC value in irrigated wheat. It was found that a dose of at least 25 kg N ha −1 should be applied at planting. At 1st irrigation (crown root initiation) stage leaf greenness cannot be quantified properly using LCC due to small leaf size and thus it did not lead to adequate fertilizer N management decision. At 2nd irrigation (maximum tillering) stage leaf colour of the first fully exposed leaf served as best indicator of inherent soil N supply as well as crop N needs and thus helped guide need-based fertilizer N top dressing for improving fertilizer N use efficiency in wheat. Fertilizer N management strategy based on application of prescriptive doses of 25 kg N ha −1 at planting and 45 kg N ha −1 at 1st irrigation and then a dose of 30 or 45 kg N ha −1 at 2nd irrigation stage depending on colour of the leaf to be ≥LCC 4 or

In the quest of enhancing nitrogen (N) use efficiency in irrigated transplanted rice beyond that observed with blanket recommendation, leaf colour chart (LCC) is being used to apply N whenever colour of the first fully opened leaf from the top is less green than a critical colour shade. So as to avoid frequent (every 7–10 days) monitoring of leaf colour, criteria were developed to apply fertilizer N at critical growth stages of rice but by adjusting the dose of N as per colour of the leaf measured with LCC. A series of experiments were carried out at Ludhiana and Gurdaspur locations from 2007 to 2010 with treatments refined progressively to work out appropriate combination of fixed and adjustable rates of fertilizer N at critical stages of transplanted rice. A dose of 30 kg N ha −1 at transplanting as prescriptive N management proved to be adequate for achieving high yields of rice. Corrective N management consisting of adjustable N doses was worked out as application of 45, 30 or 0 kg N ha −1 depending upon leaf colour to be −1 only if leaf colour is less green than LCC shade 4 at initiation of flowering. A combination of these prescriptive and corrective N management strategies resulted in optimum rice grain yield and high N use efficiency with less fertilizer N application than the blanket recommendation. For some rice cultivars, particularly in years with favorable climate, fixed date adjustable dose N management produced yield levels higher than those achieved by applying blanket recommendation for fertilizer N and resulted in agronomic efficiency higher than 25 kg grain/kg N.

Large field to field variability restricts efficient fertilizer N management when broad based blanket recommendations are used in maize (Zea mays L.). To achieve higher yields and to avoid nitrogen (N) deficiency risks, many farmers apply fertilizer N in excess of crop requirement in maize. Field experiments were conducted for five years (2005–2009) to establish and evaluate threshold leaf colour to guide in-season need based fertilizer N topdressings in four maize genotypes. Colour (of the first top maize leaf with fully exposed collar) as measured by comparison with different shades of green colour on a leaf colour chart (LCC) and maize grain yield was significantly correlated. The Cate–Nelson plot of chlorophyll (SPAD) meter/leaf colour chart values against relative grain yield of 0.93 for the experiments conducted during first two years indicated that LCC shade 5 during vegetative growth stages and LCC shade 5.5 at silking stage (R1) can guide crop demand driven N applications in maize. Evaluation of the established threshold leaf greenness during the next three years revealed that fertilizer N management using LCC 5 starting from six-leaf (V6) stage to before R1 stage resulted in improved agronomic and N recovery efficiency in different maize genotypes. There was no response to fertilizer N application at R1 stage. The study revealed that in maize, fertilizer N can be more efficiently managed by applying fertilizer N dose based on leaf colour as measured by LCC than blanket recommendation.