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Dry direct-seeded aerobic rice (DSR) is an emerging attractive alternative to traditional puddled transplanted rice (PTR) production system for reducing labour and irrigation water requirements in the Indo-Gangetic plains (IGP) of India. The fertilizer N requirement of DSR grown with alternate wetting and drying water management may differ from that of PTR grown under continuous flooding due to differences in N dynamics in the soil/water system and crop growth patterns. Limited studies have been conducted on optimizing N management and application schedule for enhanced N use efficiency in DSR. Therefore, field experiments were conducted over 3 years in NW India to evaluate the effects of N rate and timing of its application on crop performance and N use efficiency. Interaction effects of four N rates (0, 120, 150, and 180 kg ha−1) as urea and four schedules of N application on yield and N use efficiency were evaluated in DSR. The N schedules included N application in three equal split doses (0, 35...

An optical sensor-based fertilizer nitrogen (N) management strategy that relies on visible and near-infrared spectral response from plant canopies was evaluated for irrigated wheat in the northwestern India. GreenSeeker™ optical sensor-guided fertilizer N dose, computed from an estimate of potential yield and response index, takes into account both the temporal and field-to-field variabilities and is applied only once after measuring in-season spectral response from the crop canopy. Seven field experiments were conducted in four wheat seasons to decide whether to apply the optical sensor-guided fertilizer N dose at 2nd or 3rd irrigation stage and to work out the appropriate N management before applying it. Robust relationships between in-season sensor-based estimates of yield and actual wheat yields were observed both at 2nd (R 2 = 0.64) and 3rd (R 2 = 0.86) irrigation stages of the crop. GreenSeeker-based fertilizer N management resulted in high yield levels and high N-use efficiency. Application of 30 kg N ha−1 at planting and 45 kg N ha−1 at 1st irrigation was found to be the appropriate N management before applying the GreenSeeker-guided dose at 2nd irrigation stage. Grain yields obtained by following sensor-guided N management were at par with those observed with the blanket recommendation of 120 kg N ha−1, but with greater recovery efficiency (by 6.7–16.2%) and agronomic efficiency [by 4.7–9.4 kg grain (kg N applied)−1]. The major outcome of this study was that applying a moderate amount of fertilizer N at planting and enough fertilizer N to meet the high N demand during the period between crown root initiation stage and maximum tillering stage before applying a sensor-guided fertilizer N dose at 2nd irrigation stage results not only in high yields but also in high fertilizer N-use efficiency in irrigated wheat.

Increasing nitrogen fertilizer applications have sustained a growing world population in the 20th century. However, to avoid any further associated environmental damage, new sustainable agronomic practices together with new cultivars must be developed. To date the concept of nitrogen use efficiency (NUE) has been useful in quantifying the processes of nitrogen uptake and utilization, but we propose a shift in focus to consider nitrogen responsiveness as a more appropriate trait to select varieties with lower nitrogen requirements. We provide a roadmap to integrate the regulation of nitrogen uptake and assimilation into varietal selection and crop breeding programs. The overall goal is to reduce nitrogen inputs by farmers growing crops in contrasting cropping systems around the world, while sustaining yields and reducing greenhouse gas (GHG) emissions.

SUMMARYBagasse and rice husk are two important agro-industrial by-products that are used as fuel in the sugar and rice mill industries, thus producing large quantities of bagasse ash (BA; 0·05 of bagasse) and rice husk ash (0·20 of rice husk) as waste material. Applying BA and rice husk ash (RHA) to agricultural land improves yield, nutrient uptake and chemical fertility of soil, particularly with special reference to available phosphorus (P) and potassium (K). The present field experiment was conducted for 3 years to evaluate the P fertilizer value of these agro-industrial waste materials in a wheat–rice system (WRS). The experiment was laid out in a split-plot design with RHA and BA applied at 10 t/ha and including a no-amendment control as the main plot treatments and three levels of fertilizer P (0, 13 and 26 kg P/ha; designated P0, P13and P26, respectively) as sub-plot treatments to wheat in WRS. Application of fertilizer P increased the wheat grain yield up to P26in the un-amended control treatment. However, a significant response of wheat to fertilizer P was also observed up to P13in the presence of BA and RHA, thereby saving 50% of fertilizer P. Both RHA and BA increased wheat productivity by 12 and 16%, respectively, over the un-amended control. The subsequent rice crop also produced 14% higher paddy yield when the two ashes were applied along with P13to the previous wheat crop. The increases in grain yield were accompanied by significant increases in the uptake of P and K, and P content (Olsen P) in the soil. The application of recommended P (P26) in un-amended plots resulted in a negative P balance of 9·3 kg P/ha/year. On the other hand, the application of BA alone and RHA along with P13resulted in neutral/slightly positive P balance. A strong linear relationship (R2= 0·98) was observed between P balance and Olsen-P build up in the soil. It may be concluded that application of BA and RHA has the potential to increase system productivity and reduce the cost of inputs in terms of reduced application of fertilizer P to wheat and rice.

Application of fertilizer N doses to rice (Oryza sativa L.) whenever leaf greenness as measured by chlorophyll meter (SPAD) and LCC falls below a fixed threshold is being extensively used for site-specific management of fertilizer N. As fixed threshold greenness varies with regions, rice cultivars and seasons, a dynamic threshold greenness concept in the form of SPAD-based sufficiency index has been introduced. For rice, the dynamic threshold greenness is defined as 90 % of the SPAD meter reading of leaves in an Nrich or over fertilized strip. In the present investigation, four field experiments with six cultivars were conducted at two locations to test fertilizer N management following two variants of the LCC-based dynamic threshold greenness concept—the leaf greenness one or 0.5 unit less than the LCC reading of the Nrich strip (LCC-Nrich), vis-a-vis SPAD meter-based sufficiency index approach and blanket recommendation of 120 kg N ha−1 applied in three equal split doses. The fertilizer N management following threshold greenness of one unit less than the LCC-Nrich resulted in total N application of only 60 kg ha−1 and thus sub-optimum rice grain yields. The grain yield of rice, N uptake and fertilizer N use efficiency measured with N management following threshold leaf greenness of 0.5 units less than LCC-Nrich were at par with the SPAD meter-based 90 % sufficiency index approach and were better than the blanket fertilizer recommendation in the region. The LCC-based dynamic threshold greenness strategy holds promise to efficiently manage fertilizer N rice as it can effectively take care of variations in the rice cultivars, locations and seasons.

Bagasse ash (BA) and rice husk ash (RHA) contain significant quantities of P and many other nutrients. Application of biomass ashes has been shown to improve crop yields and soil properties. The present experiment was conducted to determine the effect of BA and RHA application in combination with different doses of P fertilizer on soil enzyme activities in rice–wheat rotation in the Indo-Gangetic plains of India. Both BA and RHA significantly increased the dehydrogenase, alkaline phosphatase and phytase activities as compared to no ash application in the 0–0.15 m soil layer. Activities of these enzymes also increased with P fertilization. Biomass ashes and P fertilizers showed little effect on enzymatic activities in the 0.15–0.30 m soil layer. Application of biomass ashes and P fertilization significantly increased Olsen-P and organic carbon content in soil over control. Enzyme activities were significantly and positively correlated with Olsen-P, organic carbon content and wheat grain yield. This study suggests that soil quality can be improved by applying biomass ashes and P fertilization on a loamy sand soil under rice–wheat system.

Blanket fertilizer nitrogen (N) recommendations for large irrigated transplanted rice tracts lead to low N use-efficiency (NUE) due to field-to-field variability in soil N supply and seasonal variability in yield. To achieve high NUE, a fertilizer N management strategy based on visible and near-infrared spectral response from plant canopies using a GreenSeeker™ optical sensor was evaluated. Seven field experiments were conducted during 2005–2007 at two locations in the Indo-Gangetic plains of South Asia to define relationships between in-season sensor measurements at panicle initiation (PI) stage and up to 2 weeks later, and yield of rice. During 2006–2010, seven field experiments were conducted to assess the sensor-based N management strategy and to work out the prescriptive N management to be followed prior to applying sensor-guided fertilizer dose. During 2010 and 2011, the sensor- based N management strategy was evaluated versus farmers’ fertilizer practice at 19 on-farm locations. Relationships with R2 values 0.51 (n = 131), 0.45 (n = 74) and 0.49 (n = 131), respectively, were observed between in-season sensor-based estimates of yield at 42 (PI stage), 49 and 56 days after transplanting of rice and actual grain yield of rice. Applications of 30 kg N ha−1 at transplanting and 45 kg N ha−1 at active tillering stage were found to be the appropriate prescriptive strategy before applying the GreenSeeker-guided dose at PI stage. Sensor-guided N management resulted in similar grain yields as the blanket rate farmer practice, but with reduced N rates, i.e. greater recovery efficiency (by 5.5–21.7 %) and agronomic efficiency [by 4.7–11.7 kg grain (kg N applied)−1]. This study revealed that high yields coupled with high NUE in transplanted rice can be achieved by replacing blanket fertilizer recommendation by an optical sensor-based N management strategy consisting of applying a moderate amount of fertilizer N at transplanting and enough fertilizer N to meet the high N demand during the period between active tillering and PI before applying a sensor-guided fertilizer N dose at PI stage of rice.

Site-specific N management using GreenSeekerTM was evaluated in direct-seeded rice.Panicle initiation is the appropriate stage to make corrective N management.Two algorithms for N management based on GreenSeekerTM proposed in this study.The proposed algorithms could maintain high grain yield and high N-use efficiency. To reduce the amount of wasted reactive nitrogen (N) reaching the environment and to achieve high N fertilizer use efficiency, a site-specific N management strategy using GreenSeeker� optical sensor (GS) was evaluated in dry direct-seeded rice (DDSR) in the north-western India. Four field experiments were conducted during 2011-2013 to develop an optical sensor algorithm for fine tuning in-season N fertilizer applications. It was demonstrated that panicle initiation of rice is the appropriate stage for applying GS guided N fertilizer dose. Application of a prescriptive dose of 60kgNha-1 in two or 90kgNha-1 in two or three equal split doses, followed by a corrective N dose guided by GS at panicle initiation stage resulted in rice yield levels comparable to that obtained by following general recommendation, but with lower total N fertilizer application. On an average, N use efficiency was improved by more than 12% when N fertilizer management was guided by GS as compared to when general N fertilizer recommendation was followed. The results prove the inadequacy of general recommendations for N fertilizer management in DDSR and possibility of increasing N use efficiency along with high rice yield levels through site-specific N fertilizer management using GS.

Rice husk ash (RHA) and bagasse ash (BA) are available in large quantities in South Asian countries growing rice and sugarcane. Land application of RHA and BA is likely to influence chemistry of soil phosphorus (P) and thereby P adsorption and desorption. Laboratory studies were carried out to investigate the short-term and long-term effects of RHA and BA application on P adsorption and desorption in an alkaline soil under a wheat–rice system. Addition of RHA or BA (10 Mg ha−1) resulted in a significant decrease in P adsorption compared to the control. The decrease in P adsorption was lower when RHA and BA were applied to either rice or wheat as compared with when applied to both the crops. The BA was more effective in reducing P adsorption than RHA because of its greater P concentration. Fresh addition of RHA and BA at 1% (dry-weight basis) showed a small effect on P adsorption as compared to their long-term application. The Frendulich isotherm equation gave better fit with the experimental data than the...

Prediction of potential yields during crop growth season is important for successful agricultural decision-making. The objective of this study was to predict grain yield of dry direct-seeded rice (DDSR) using leaf greenness as measured by chlorophyll meter (SPAD) and leaf color chart (LCC) and using normalized difference vegetation index (NDVI) worked from GreenSeeker optical sensor measurements. Regression analysis was performed to predict rice grain yield at maturity from the LCC, SPAD and NDVI readings recorded from two multi-rate nitrogen level experiments conducted in two consecutive rice seasons. The measurements made at early growth stage could not explain satisfactorily the variations in rice grain yield. Predictions made by the LCC were not reliable. The SPAD meter was superior to the LCC at booting growth stage. The NDVI readings at panicle initiation growth stage exhibited the highest coefficient of determination and explained 63% of the variation in rice grain yield. Yield predictability with SPAD measurements at 70 and 84 DAS, and NDVI readings at 70, 84 and 98 DAS did not improve by introducing the element of cumulative growing degree days (CGDD). However, CGDD based SPAD meter readings at 98 DAS, and LCC readings at 70, 84 and 98 DAS improved the crop yield predictability. The regression models were validated on an independent data set obtained from experiment conducted in the same area. The root mean square error (RMSE) for NDVI and SPAD readings was lower than the LCC readings. On the contrary, adjusting the LCC score with CGDD reduced the RMSE. The study reveals that yield of DDSR can be satisfactorily predicted with in-season measurements of NDVI, SPAD meter and the LCC scores adjusted with CGDD.

In the Indo-Gangetic plain in South Asia, fertilizer nitrogen (N) application to irrigated wheat in two split doses at planting and at crown root initiation (CRI) stages of the crop is the general recommendation. Farmers have a tendency to apply another dose of N at maximum tillering (MT) stage to avoid the risk of N deficiency. However, appropriate criteria to decide MT stage application of N are lacking. Field experiments were conducted for three seasons with four wheat cultivars to develop criteria for using a chlorophyll (SPAD) meter and an optical sensor (GreenSeekerTM) for guiding MT stage N application. Application of 0, 60, 80, 100 and 120 kg N ha−1 in two equal split doses at planting and at CRI stage constituted the main plots. The two subplots consisted of applying 0 and 30 kg N ha−1 at MT stage immediately after taking SPAD meter and GreenSeeker readings. Greenness of wheat leaves at MT stage was found to be a function of N applied at planting and CRI stages. Wheat grain yield at maturity was determined by the level of greenness of leaves at MT stage—whether measured by SPAD meter or GreenSeeker (expressed as in-season estimate of yield (INSEY) computed by dividing normalized difference vegetation index by number of days between planting and sensing). Grain yield response to N application at MT regressed against SPAD readings at MT revealed that an application of 30 kg N ha−1 will increase wheat yield by 1.0 or 0.5 t ha−1 when color of the wheat leaves was equivalent to or less than SPAD value of 32.5 or 42.5, respectively. Robust regression between grain yield response and INSEY values revealed that application of 30 kg N ha−1 at MT will lead to a grain yield increase by 1.0 or 0.5 t ha−1 if INSEY values were found to be 0.005 or 0.011, respectively. It should serve as an easy and useful criterion for applying a supplementary dose of fertilizer N at MT stage of wheat.

Fertile soils are a fundamental asset for a sustainable rice–wheat cropping systems followed in 13 Mha in the Indo-Gangetic plains (IGP). Managing practices for the rice–wheat cropping system are changing and in turn influencing soil fertility parameters. In long-term rice–wheat cropping, soil organic carbon content declined only in soils having high initial organic carbon content. Otherwise, soil organic carbon content tends to remain unchanged or increase with continuous cropping and fertilizer/manure applications. Available P content of the soil also increased with P additions through fertilizers or manures. Soil quality deterioration with respect to K supplying power is being largely overlooked. Deficiency of zinc is widespread in the IGP, but with the extensive use of zinc sulfate, it has reduced in some areas. Deficiency of Fe, Mn, and B is also increasing. The western transects of the IGP are more productive not only because radiation decreases and minimum temperature increases from eastern to west...

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.

Ascochyta rabiei isolates were characterised for their variability using a set of host differentials following cloth chamber screening technique. Sixty chickpea genotypes were evaluated against the characterised 10 individual pathotypes separately to identify genotypes with stable resistance during 2007–2008. Twenty four genotypes showed resistance to all the pathotypes; whereas 18 genotypes were resistant to moderately resistant to these pathotypes. The above genotypes can be considered good sources of stable resistance and recommended as donors or for direct cultivation in north western plain zone of India.

Blanket fertilizer nitrogen (N) recommendations for large irrigated wheat tracts lead to low N-use efficiency due to field-to-field variability in soil N supply and seasonal variability in yield. To achieve high N use efficiency, a site-specific N management strategy using GreenSeeker™ optical sensor was evaluated. We conducted seven field experiments during 2004–2006 at three locations to define relationships between in-season sensor measurements and yield of wheat and to know whether response of wheat to fertilizer N can be estimated by sensor measurements. During 2005–2007, four field experiments were conducted to assess the sensor-based N management strategy and to work out prescriptive N management to be followed prior to applying sensor-guided fertilizer dose. We observed robust relationships between in-season sensor-based estimates of yield at Feekes 5–6 and 7–8 stages and actual wheat yields. Response of wheat to fertilizer N defined by the sensor was highly correlated with harvest response index. Sensor-guided fertilizer N applications resulted in high yield levels and high N-use efficiency. Application of 90 kg N ha-1 at planting or in two equal doses at planting and crown root initiation stage was the appropriate prescriptive fertilizer N management. This study reveals that high N-use efficiency in irrigated wheat can be achieved by replacing blanket fertilizer recommendation by an optical sensor-based N management strategy consisting of applying moderate amount of fertilizer N at planting and crown root initiation stages and sensor-guided fertilizer N dose at Feekes 5–6 or 7–8 stages of wheat.

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.

Fertilizer nitrogen (N) is one of the major inputs in rice–wheat production systems in South Asia. As fertilizer N has generally been managed following blanket recommendations consisting of two or three split applications of preset rates of the total amount of N, improvement in N use efficiency could not be achieved beyond a limit. Feeding crop N needs is the most appropriate fertilizer N management strategy to further improve N use efficiency. Since plant growth reflects the total N supply from all sources, plant N status at any given time should be a better indicator of the N availability. The chlorophyll meter and leaf colour chart have emerged as diagnostic tools which can indirectly estimate crop N status of the growing crops and help define time and quantity of in-season fertilizer N top dressings in rice and wheat. Supplemental fertilizer N applications are thus synchronized with the N needs of crop. The chlorophyll meter may not be owned by South Asian farmers individually, but it can be made available to farmers through village cooperatives, extension specialists, and crop consultants. Leaf colour chart, a simple and cost-effective device has already penetrated into South Asian farming and increasing numbers of farmers are finding it helpful in efficiently managing N fertilizers. This paper reviews the results of investigations carried out using these diagnostic tools in managing need based N applications in rice and wheat in South Asia.

In irrigated wheat as grown in north-western India, fertilizer nitrogen (N) management following blanket recommendations is increasing resulting in stagnant yield levels with low N use efficiency. Site-specific nutrient management strategy to apply N as per need of wheat crop was formulated based on leaf colour measured by chlorophyll meter (Minolta SPAD meter) as a function of soil N supply. The SPAD meterguided protocols for fertilizer N application at crown root initiation (CRI) and maximum tillering (MT) stages, coinciding with first two irrigations, were evaluated through a series of field experiments with seven wheat varieties in Ludhiana and Gurdaspur in north-western India. Threshold leaf greenness levels equivalent to SPAD readings

Neem coated urea (NCU) applied to rice can result in high N use efficiency as it contains nitrification inhibition properties. Field experiments were conducted for three years (2005–2007) at Ludhiana (sandy loam soil) and Gurdaspur (clay loam soil) for evaluating the relative performance of NCU vis-a-vis ordinary urea as a source of N for transplanted wetland rice. Along with a no-N control, the two N sources were tried at three N levels––40, 80 and 100% of the recommended level of 120 kg N ha−1. Different doses of N were applied in three equal split doses at transplanting, 21 and 42 days after transplanting (DAT). For need based site specific N management for improved N use efficiency, the two sources of N were applied using leaf colour chart (LCC). In this treatment a basal dose of N at the rate of 20 kg N ha−1 was applied after 7 DAT and LCC readings were recorded at weekly intervals starting 14 DAT. Whenever the intensity of green colour of the first fully opened leaf from the top was less than shade 4 of the LCC, N was applied at the rate of 30 kg N ha−1.

Leaf colour chart (LCC) guides fertilizer nitrogen (N) application to rice as per requirement of the crop on the basis of a critical leaf colour. We evaluated need-based N management in on-farm experiments at 350 locations in the Indian Punjab during 2002 – 2005. Following LCC-based N management, from 9.4 – 54.2 kg N ha−1, with an average of about 25% less fertilizer N was used, without any reduction in yield as compared to the practice of farmers of applying blanket N at fixed time intervals. Application of fertilizer N when colour of the first fully expanded leaf was less than LCC shade 4, increased nitrogen use efficiency from 48 – 65 kg grain kg N−1. Nitrogen requirement of rice was site-specific both in terms of time and the amount of fertilizer N applied. In 36% of the experiments, a dose of fertilizer N was applied 55 days after transplanting (DAT) of rice. Also there were cases where only one top dressing of N was required. The study reveals that practice of applying N at fixed growth sta...

The contribution of different sized soil separates to various inorganic P fractions was investigated after 32 years of long-term fertilization under maize-wheat-cowpea fodder crop rotation. Phosphorus was applied as single super phosphate. A major portion (71.5%) of Olsen-P was extracted from sand size particles, and only 11.4% and 17.1% was present in silt and clay size separates of the surface soil layer, respectively. Unlike Olsen-P, Al-P and Fe-P in soil were mainly present in the clay fraction of the soil. Percent contribution of clay, sand and silt particles in the surface layer was 61.5, 27.4 and 11.1 to Al-P, and 66.4, 21.6 and 12.0 to Fe-P, respectively. However, Ca-P in surface soil layer was mainly (68%) present in sand size soil separates followed by silt (28.5%) and clay (3.5%) size soil separates. Percent distribution of P forms in different sized soil separates of the subsurface layer also followed the same pattern, but there was little decrease in the contribution of sand with a corresponding increase in the contribution of silt and clay size soil separates. X-ray diffractograms specified the precipitation of residual fertilizer P as octa-calcium phosphate, hydroxy apatite and variscite, after reacting with calcium and aluminum in the soil. The peaks recognizing the presence of these reaction products were observed only in sand and silt size soil separates. However, no peak was found in clay sized soil separates.

Phosphorus availability from residual P sources in soil is virtually the chemistry of metastable P compounds, i.e., their solubility and interaction with other soil and plant components. Identification of these compounds in soils under long-term application of fertilizers and farmyard manure is unstated and is prerequisite to comprehend the processes of P transformations and cycling in soil-plant system. X-ray diffraction analysis of surface and subsurface soils fertilized for 32 years under a maize–wheat–cowpea (fodder) cropping sequence revealed that P reaction products in soil depends upon the kind of fertilizer added to the soil as well as on management practices. Precipitation of applied P occurred mainly as octa-calcium phosphate, hydroxy apatite and variscite. In addition to these compounds, precipitation as \(\hbox{CaNH}_{4}\hbox{PO}_{4}\cdot\hbox{H}_{2}\hbox{O}\) was also observed in soil receiving diammonium phosphate rather than super phosphate as a fertilizer P source. Continuous application of farmyard manure (FYM) for three decades inhibited the conversion of applied P to more stable forms such as variscite and hydroxy apatite. The different P reaction products govern the availability of residual soil-P to growing plants. The reaction products formed were associated only with the sand and silt fraction of soil. Phosphorus in the clay fraction is mainly P adsorbed on exchange complexes or entrapped in lattice of silicate minerals.

Transformations of applied phosphorus (P) to unavailable residual soil P is the major cause of limited P supply in most of the P-deficient soils. The effect of the incorporation of crop residues (rice straw [RS] and wheat straw [WS]) and organic manures (farmyard manure [FYM] and green manure [GM]) on P release in soil and its bio-availability to various summer and winter crops was investigated in laboratory and screen house experiments. Surface (0–0.15 m) soil samples collected after 32 years of differential fertilization to maize–wheat–cowpea fodder crop rotation, were examined for adsorption/desorption behavior of P, after incubating with organics of varying C:P ratios. Incorporation of crop residues increased P adsorption maxima as well as resistance to P release in soils. Increased buffering capacities in crop residue-incorporated treatments decreased P desorption in soil, whereas the incorporation of organic manures decreased P sorption, maximum buffering capacity (MBC), bonding energy, and increased P concentration in soil solution. Although the incorporation of crop residues decreased P release in soil its bio-availability in the soil–plant system was crop-specific and varied with the time of incorporation of organics. Raya showed increased P uptake with incorporation of both RS and WS, whereas in the case of berseem increased P uptake occurred only with wheat straw. Phosphorus uptake in rice, maize, and soybean decreased with the incorporation of both RS and WS. Incorporation of crop residues 1 day before the sowing of summer crops decreased P uptake, whereas incorporation 3 weeks prior to the sowing of winter crops improved P bio-availability. Incorporation of organic manures with a narrow C:P ratio, however, improved P uptake in all the crops under investigation, in both the seasons. The results thus emphasized that adsorption parameters calculated from the examination of soil samples should not be used independently for making fertilizer P recommendations. Crop effects (root exudates) and their interaction with P reaction products in soil and synchronization in P release from organics and crop uptake need to be considered to understand the virtual behavior of P bio-availability in the soil–plant system.

An understanding of the adsorption–desorption behaviour of phosphate (P) in soils after three decades of long-term fertilization would be an invaluable supplement to our knowledge of the chemistry of P in soils and would assist in developing P application strategies for successive crops. With this objective and within the framework of a long-term experiment, we collected surface soil samples (0–0.15 m) from agricultural crop land on which a rotation of maize-wheat-cowpea (fodder) crops had been grown for 32 years. The soil samples were investigated for adsorption and desorption behaviour of P, and the buffering capacities of soil samples were computed from the adsorption data. Soils differed widely in their P supply characteristics. Phosphate adsorption increased while percentage P adsorbed decreased gradually with increasing levels of added P. Adsorption maxima and the extent of P adsorption was at its maximum in unfertilized soil, and P adsorption decreased with increased P applications. The incorporation of farmyard manure with optimal P levels decreased P adsorption even more than a super-optimal application of P fertilizers. Bonding energy and Freundlich constant ȁ8nȁ9 also decreased with increased P application and with the incorporation of farmyard manure. The adsorption and desorption of applied P were inversely related, and the soils that adsorbed P the most readily released it the least into the soil solution, and vice-versa. Computation of maximum buffering capacities (MBC) indicated that increased levels of P application decreased MBC and increased P supply in soil. The beneficial effects of an annual incorporation of farmyard manure with optimal P levels were clearly pronounced, and P availability in these soils was found to be even higher than the soil receiving the super-optimal application of P fertilizers. Various adsorption–desorption parameters were significantly related with the P uptake of different summer (rice, maize, soybean) and winter (wheat, berseem and raya) crops. Adsorption maxima, desorption maxima and maximum buffering capacity are the major parameters governing P availability in soils.

Use of high rates of commercial nitrogen (N) fertilizers over the years has resulted in adverse effects on soil and environment health. Integrated use of fertilizer N and organic N sources is expected to reduce the N losses and improve N use efficiency. The present field experiment was conducted for two years to evaluate the effects of commercially available multi-strain inoculant ‘Fertimine’ and farmyard manure (FYM) applied at variable rates of fertilizer N on the nutrition of rice-wheat system. Four treatment combinations of FYM (15 t ha-1, fresh weight) and fertimine were applied to main-plots and four N levels to sub-plots in factorial split-plot design. In the absence of fertimine and FYM, significant increase in rice yield was observed up to 120 kg N ha-1 during first season and 80 kg N ha-1 during second season. The application of FYM and fertimine significantly increased mean grain yield of rice by 12 and 5 per cent over no FYM and fertimine, respectively. Significant interaction effect of fertimine and fertilizer N observed on rice grain yield suggested that fertimine significantly increased the rice yield at low rates of fertilizer N. While fertilizer N and FYM caused significant increase in the total uptake of N, P and K in rice, fertimine showed significant increase in total P uptake only. The FYM applied to rice showed significant residual effect on the yield and total N, P and K uptake in the subsequent wheat. Application of FYM significantly improved the soil chemical and biological properties after two cycles of rice-wheat rotation.