HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Kapoor, V. Articles by Diamond, R. Search for Related Content PubMed Articles by Kapoor, V. Articles by Diamond, R. Agricola Articles by Kapoor, V. Articles by Diamond, R. Related Collections Rice Other Crop Management Best Management Practices Nutrients Nutrient Management

FERTILIZER MANAGEMENT

Rice Growth, Grain Yield, and Floodwater Nutrient Dynamics as Affected by Nutrient Placement Method and Rate

^a Indira Gandhi Agricultural University (IGAU), Krishak Nagar, P.O. Box 94, Raipur (CG), 492006, India
^b International Center for Soil Fertility and Agricultural Development (IFDC), P.O. Box 2040, Muscle Shoals, AL, 35662

^* Corresponding author (usingh{at}ifdc.org).

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The loss of major nutrients can be high in rice (Oryza sativa L.) fields, particularly rainfed rice, where water flowing from field to field during periods of high rainfall not only reduces the nutrient use efficiencies but also has the potential for environmental degradation. We examined the influence of deep point placement of N, P, and K briquettes compared to broadcast incorporation of N, P, and K on floodwater nutrient loads after fertilizer application and on the performance of wet season rice in a Vertisol. Broadcast application of N as urea resulted in an average 10 times higher amounts of ammonium N in floodwater compared to deep placement of urea briquette. The broadcast application of single superphosphate resulted in 67 times higher amounts of P in floodwater than plots receiving deep placed P. The floodwater NH₄⁺–N and P content in the deep placement treatments were negligible—similar to floodwater N and P content without fertilizer application. The floodwater K amounts were also significantly lower with deep placed N–P–K briquettes. Significantly higher grain and straw yields, total N, P, and K uptake, and N and P use efficiencies were observed with deep placement of N–P–K compared to broadcast application of N–P–K. Deep placed N–P briquettes gave significantly higher grain yield, straw biomass, total P and K uptake, apparent P recovery, and agronomic N and P use efficiencies when plant spacing was reduced from 20 by 20 cm to 20 by 10 cm. Closer plant spacing led to better utilization of P and K and provided opportunities for deep placement of N–P or N–P–K briquettes in soils with low available P. Combining site specific characteristics (high soil pH, low percolation rate, high rainfall and surface runoffs) with plant spacing and N–P–K briquettes prepared based on site-specific nutrient requirements offers potential for higher yields, improved fertilizer use efficiency, balanced fertilization, and reduced nutrient losses.

Abbreviations: AR, apparent fertilizer N recovery • AR_p, apparent recovery of applied P • DAP, diammonium phosphate • MOP, muriate of potash • NUE, nitrogen use efficiency • PU, prilled urea • PUE, agronomic use efficiency of applied P

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.

Received for publication January 3, 2007.

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
DEEP PLACEMENT OF UREA in lowland rice fields has been widely recognized as an effective management practice for transplanted rice, except on soils with a high percolation rate (Savant and Stangel, 1990; Misra et al., 1995; Bowen et al., 2005). Deep placement involves placement of large ( >1 g) granules or briquettes of fertilizer, particularly urea at least 10 cm below the soil surface. The deep placement of urea briquettes helps in reducing N losses from ammonia volatilization and surface runoff, which are the most important mechanisms of N loss from lowlands in rice production areas. The flowing water in periods of high rainfall carries significant amounts of P and K as well as N. The nutrient flushing also depends on rainfall intensity. These are some of the key factors in addition to water management and weed control for low fertilizer use efficiency in rice. Studies indicated that a high percentage of applied nutrients could be present in floodwater after fertilizer application (Singh et al., 1995). This increases the chance of runoff losses, particularly in the situation where water flows from field to field without any drainage systems (Wetselaar et al., 1985). The nutrient-enriched runoff water has the potential for environmental pollution. The P in runoff is particularly important due to increased eutrophication in water bodies. Deep placement of nutrients not only has a positive agronomic impact but also an environmental benefit by reducing the nutrient load in runoff waters and reducing both volatilization and denitrification losses (Savant and Stangel, 1990). In the lowlands of eastern India, and in many Asian countries, there is no effective drainage system in rainfed rice lands or in many irrigated rice lands. Thus, deep placement of urea-diammonium phosphate (DAP)-muriate of potash (MOP) granules can significantly help to increase the nutrient use efficiencies and improve the environmental quality under such conditions.

We examined the effect of deep placement of urea-DAP-MOP on nutrient load in floodwater, rice grain yield, straw biomass, nutrient uptake, and nutrient use efficiencies in the lowland Vertisol of eastern India. Apart from the agronomic and environmental benefits, the deep placement of N–P–K briquettes would consolidate labor requirement compared to urea deep placement and broadcast incorporation of P and K. The N–P–K briquettes further provide opportunities for site-specific nutrient management.

The selection of the study area was based on socioeconomic and agroclimatic conditions most suitable for deep placement of nutrients (Thompson, 1992; Mohanty et al., 1999). The area is characterized by relatively low labor cost ( <$1 per day), abundance of labor, and small farm size ( <1–2 ha). The rainfall is quite high (1200–1400 mm during June–September). The soils have moderate-to-high cation exchange capacity (CEC) (20–40 cmol_c kg^–1) and low permeability after puddling and submergence (2–5 mm d^–1) with neutral to slightly alkaline pH (6.9–8.2). The availability of labor, small farm size, and high potential for runoff and volatilization losses would favor deep placement of fertilizer briquettes over broadcast application of conventional fertilizers.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Location and Weather Conditions
Field experiments were conducted to evaluate the effectiveness of deep point placement of N, P, and K in briquette forms on rice (var. Mahamaya). Mahamaya is a widely grown gall midge-resistant medium duration (116 ± 4 d from sowing to maturity) variety with grain size of 0.03 g (Tomar et al., 2004). The experiment was conducted during the wet season of 2001 and 2002 at Indira Gandhi Agricultural University (IGAU), Raipur, Chattisgarh, India, under rainfed conditions with supplemental irrigation for land preparation and crop establishment. The experimental site is situated at 21°4' N latitude and 81°39' E longitude and has an altitude of 293 m above sea level in the eastern part of India. The climate is subhumid with an average annual rainfall of 1250 mm, primarily received from June to October. Daily rainfall, solar radiation, and air temperature for two cropping seasons are shown in Fig. 1 . The soil is fine, montmorillonitic, hyperthermic, Udic Chromustert (Arang II series). It is deep, heavy clay, and dark brown in color. Soil is calcareous (CaCO₃ 17%), slightly alkaline in reaction (pH 7.5), high CEC (38.8 cmol⁺ kg^–1), organic carbon (5.7 g kg^–1), Olsen P (13.2 kg ha^–1), and has a high K content (exchangeable K 357 kg ha^–1).

View larger version (29K): [in this window] [in a new window]   Fig. 1. Weather conditions as represented by daily rainfall (mm), maximum and minimum temperature (°C), and sunshine duration (h) during the 2001 and 2002 experimental years.

Eighteen treatments were designed to evaluate crop responses to the broadcast incorporation of N, P, and K, deep placement (at 10-cm soil depth) of N, N–P, and N–P–K briquettes, and to facilitate the estimation of N and P efficiencies (Table 1 ). The treatments were selected to approximate farmers' practice (50 kg N, 13 kg P, and 25 kg K ha^–1), current recommendations of 80 kg N, 22 kg P, and 25 kg K ha^–1, and 120 kg N, 28 kg P and 25 kg K ha^–1 for achieving maximum yields as given by IGAU extension service. Application of nutrients through briquettes also posed restrictions in choosing the treatment combinations; hence the experimental rates are not identical to farmers' practice and recommended rates. Treatment 18 was included to evaluate influence of planting spacing on effectiveness of deep placement.

Briquette Production
Briquettes of different size were prepared to provide different nutrient combinations and rates (Table 1). The N rates were fixed at 53 or 78 kg ha^–1 for deep placement of N alone when using one briquette of either 1.8 g or 2.7 g per placement site at 40 by 40 cm spacing (62,500 placement sites per ha), respectively.

Possible rates of P and/or K in combination with N at 53 or 78 kg ha^–1 were calculated for a machine that produces a larger size (volume) briquette or using two briquettes. The N–P–K combinations in the briquette are based on the specific densities of the fertilizer materials used and the size (volume) of the briquette. For example, 1.8 g and 2.7 g urea briquette machines have briquette sizes of 1.35 cm³ and 2.0 cm³, respectively. The specific densities are: urea = 1.33, DAP = 1.71, and MOP = 2.00 g cm^–3.

Soil and Plant Sampling
Initial soil samples from the experimental field were analyzed for their physicochemical properties. Grain and straw yields were recorded at harvest from a 25-m² area at the moisture level of 140 g H₂O kg^–1. Grain and straw samples for aboveground biomass were collected at harvest and analyzed for determination of nutrient uptake of N (acid digestion and distillation as described in Bremner [1960]), P (vanadomolybdate yellow color using spectrophotometer [Olsen and Sommers, 1982]), and K (flame photometry [Knudsen et al., 1982]). The CEC and exchangeable K were determined by extraction with 1M ammonium acetate, Olsen P was determined by extraction with sodium bicarbonate (Olsen et al., 1954), organic C was determined by oxidation with potassium dichromate (Nelson and Sommers, 1996), and texture was determined by the pipette method (Day, 1965).

Floodwater Measurements
After transplanting floodwater depth was periodically recorded. A bamboo stake of 2 cm width by 20 cm length, marked in 0.5 cm graduations was used (5 cm of which was inserted into the soil). Floodwater depth was recorded daily from four spots per plot for the first 10 d after fertilizer application only. A floodwater-sampling scoop was fabricated using a bamboo pole (about 2 m long) and attaching a 100-mL plastic beaker to the end of the pole. Two floodwater samples (each of 250–300 mL) were collected from four equally spaced locations in each plot using this floodwater-sampling scoop. The floodwater samples were covered and immediately brought to the laboratory. Floodwater pH was determined using 25-mL sample. The floodwater samples were filtered and 1 mL of 10% phosphoric acid was added to the sample used for NH₄⁺–N estimation before placing in deep freeze using 250 mL plastic bottles. The samples were analyzed at the earliest possibility for NH₄⁺–N following the micro-Kjeldahl distillation-titration procedure (Bremner and Keeney, 1966). The remaining floodwater was used for analysis of K using flame emission spectrophotometer (Knudsen et al., 1982) and phosphorus colorimetrically by the ascorbic acid method (Olsen and Sommers, 1982). Additional floodwater samples during 2002 season were taken from a neighboring field where no fertilizer (N, P, and K) was applied.

Statistical Analysis
Yield, N use efficiency, N, P, K content, and N, P, K uptake data were processed with analysis of variance using a model where the effect of years (main plots) was tested with the interaction block x year and the effects of treatment and treatment x year were tested with the term block x treatment nested in years. Multiple mean comparisons were performed with the Least Significant Difference (LSD) and Duncan's multiple range test (DMRT). Orthogonal contrasts were also employed to compare yields from groups of means both from the treatments and the interaction year x treatment. Error terms mentioned above were used depending on whether the test was for treatments or for the interaction treatment x year.

Floodwater N, P, and K content through the first 10 d after fertilizer application was analyzed with repeated measures analysis of variance. The significance test for treatments and their interactions with days and/or years was performed with the Wilks' Lambda criterion (Srivastava and Carter, 1983).

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Dynamics of Floodwater Ammonia–Nitrogen
The changes in floodwater ammonia-N were monitored for 10 consecutive days after N application. The results clearly indicated that the deep placement of fertilizer N resulted in significantly lower amounts of floodwater NH₄⁺–N in both years (Fig. 2 ). The significance test for treatments and their interactions with days and years was highly significant (P < 0.001) for all the floodwater NH₄⁺–N, P, and K; hence the results as presented in Fig. 2 to 4 were not combined. The differences between years may be attributed to rainfall pattern during the time of fertilizer application (Fig. 1).

View larger version (35K): [in this window] [in a new window]   Fig. 2. Dynamics of floodwater NH4+–N as influenced by N rates and application methods–broadcast incorporation of urea vs. deep placement of briquettes–for 2001 and 2002 season.

View larger version (13K): [in this window] [in a new window]   Fig. 3. Dynamics of floodwater P as influenced by deep placement, conventional application of P, and P rates.

View larger version (10K): [in this window] [in a new window]   Fig. 4. Dynamics of floodwater potassium as influenced by deep placement of N–P–K briquettes and broadcast incorporation of N, P, and K.

The floodwater NH₄⁺–N in the case of PU was highest during the initial 4 to 5 d after application; thereafter, it declined sharply. However, for the deep placed briquettes the floodwater NH₄⁺–N remained negligible throughout the 10-d study period. Floodwater ammoniacal-N is proportional to the partial pressure of ammonia, which is directly proportional to ammonia volatilization (Fillery and Vlek, 1986). Hence, the amount of ammoniacal-N present in floodwater provides an estimate for potential volatilization loss. The potential ammonia volatilization losses from the rice fields of the study area will be high because of high pH and temperature. The pH of floodwater was above 8.0 and the mean temperature ranged from 30° to 32°C (the daytime maximum temperature was even higher—Fig. 1). The conversion of ammoniacal-N to ammonia increases sharply when the floodwater pH is above 8 (Fillery et al., 1984; Samson et al., 1987). Urea hydrolysis and ammonia volatilization loss increases with temperature increase (Freney et al., 1981).

Deep placement of N reduces ammonium N in floodwater. This not only improves fertilizer N use efficiency in flooded rice but also minimizes N loss resulting from ammonia volatilization and denitrification (Savant and Stangel, 1990; Mohanty et al., 1999). It also reduces the chance of fertilizer-related environmental pollution by minimizing N runoff and volatilization losses. The sharp decline in the amount of floodwater NH₄⁺–N, 4 to 5 d after broadcasting and incorporation of PU may be attributed to volatilization loss, diffusion of NH₄⁺–N into soil, and/or nitrification in the oxidized soil layer (Godwin and Singh, 1998). The latter may also result in denitrification losses. The expected amounts of NH₄⁺–N will be even higher under a farmer's practice where PU is broadcast into the floodwater without any incorporation.

Dynamics of Floodwater Phosphorus
The floodwater P content was higher when P applied as SSP was broadcast and incorporated at puddling than for deep-placed N–P and N–P–K briquettes (Fig. 3). The floodwater P content declined sharply up to Day 5 and then it maintained a constant level similar to the zero-P treatment. The floodwater P amounts increased with increasing rates of broadcast P application in both years. Almost no floodwater P was detected 1 d after deep point placement. The floodwater P content of all the deep point placement treatments (independent of rate) was similar to the treatment where no P fertilizer was applied (Fig. 3). These results are consistent with greenhouse findings where no ³²P was detected in floodwater when urea-DAP containing ³²P was deep placed (IFDC, unpublished data).

The overall decline in the amount of floodwater P over time may be attributed to rapid soil sorption of P, diffusion of P from floodwater to soil, and fixation of P by algal activity. The observation from this field trial clearly indicates that runoff losses of P in solution and/or P sorbed on clays suspended in the flowing floodwater would be reduced substantially by application of P briquettes, thus practically eliminating P pollution/eutrophication from paddy fields. The deep placement of urea-DAP would thus have its greatest impact when climatic and field conditions are prone to high runoff losses.

Dynamics of Floodwater Potassium
The deep point placement of K helped in maintaining significantly lower amounts of K in floodwater in both years than with broadcast incorporation of K. Since the amount of floodwater K among the various briquette treatments and among the broadcast treatments were not significantly different the results were combined to emphasize the differences between two methods of K application (Fig. 4). The floodwater K content did not decline as sharply as ammoniacal-N and P.

The greater variability in floodwater K content compared with floodwater ammoniacal-N and P with deep-placed briquettes may be attributed to the high exchangeable soil K level. Since the deep placement of briquettes was very effective, as evident from negligible amounts of N and P in those treatments, the higher amounts of K in floodwater thus can be attributed to diffusion from soil. Unfortunately, the experiment did not have a zero K treatment. However, floodwater samples taken from a nearby field where no fertilizer was applied had mean NH₄⁺–N, P, and K content of 0.008, 0.005, and 0.6 g m^–2, respectively. These results verify that the deep placement of N–P–K briquette did not result in increased amounts of these nutrients in the floodwater.

Rice Response to Nitrogen Deep Point Placement
Rice grain yield, straw yield, nutrient uptake, and nutrient use efficiencies were determined to evaluate the effect of nutrient deep point placement. The summary response to all treatments is presented in Table 2 . Straw yield, P uptake, and K uptake results were combined for 2001 and 2002 because treatment x year interactions was not significant; all other results are presented for both years.

View this table: [in this window] [in a new window]   Table 5. Comparing the effect of straw biomass, total P uptake, and total K uptake to (i) N and P rates, (ii) application by broadcast (BC) incorporation, and (iii) application by deep placement of N, N–P, and N–P–K briquettes. The K rates for all the treatments remained at 25 kg K ha–1.

The soil had low-to-moderate levels of Olsen P (13.2 kg ha^–1), and we observed P deficiency symptoms due to P deep point placement on rice during the early growth stages. This effect disappeared by PI stage. The lag time for the roots to access deep-placed P vs. uniformly-broadcast P may result in poor crop growth and yields. Such an effect will be crucial for soils with very low to low P status.

Increasing rates of P (0, 14, and 28 kg P ha^–1) when broadcast incorporated with PU at a constant rate of 53 kg N ha^–1 resulted in significant yield increases (Fig. 5 ). The doubling of rice grain yield with 14 kg P ha^–1 application in 2002 indicates that the soils were indeed P deficient. However, in 2002 there was no significant yield increase beyond 14 kg P ha^–1 application. During both the years, there was a significant grain yield increase with P rates when N (78 kg N ha^–1) and P were deep placed compared to broadcast application of N and P (Table 4). Similar P response was obtained for straw yield and total N and P uptake (Tables 4 and 5).

View larger version (15K): [in this window] [in a new window]   Fig. 5. Rice grain yield response to rates of P application with broadcast incorporation of SSP, urea at 53 kg N ha–1 and 25 kg K ha–1. Bars with same letters for a given year are not significantly different at LSD5%.

Rice Response to Nitrogen–Phosphorous–Potassium
Overall the rice grain yields showed significant response to N application in both years (Fig. 6 and Table 2). Maximum grain yields, in general, were obtained with deep-placed N and at lower N rates than with conventionally applied PU. The response to P is also evident from Fig. 6 and as previously discussed (Fig. 5). As mentioned earlier there was no significant response to K fertilization.

View larger version (14K): [in this window] [in a new window]   Fig. 6. Rice grain yield response to N as influenced by P rates and N application method (deep-placed urea-N briquette vs. conventionally applied prilled urea) for 2 yr with a common K rate of 25 kg ha–1.

Fertilizer Nitrogen and Phosphorus Use Efficiency
Deep placement of N increased the agronomic N use efficiency (NUE) and apparent fertilizer N recovery (AR) in both years (Table 7 ). Even during 2002, when yields were low, deep placement of N resulted in NUE of 24 to 37 kg grain increase per kg N applied, compared with 21 to 27 kg grain increase per kg N applied using conventional N application. The agronomic NUE under farmer's condition varies between 10 and 20 kg grain yield per kg N at 40 kg N level. During both the years, AR for deep-placed N was significantly greater than conventionally applied PU. The deep placement of K also resulted in numerically higher NUE and AR, but it was not significantly different. In general, there was no significant effect on NUE and AR due to the deep placement of P and K (comparison of N–P–K briquette with N briquette). However, during 2002 AR was significantly lower for N–P–K briquettes compared with N briquette when the P rate was only 14 kg P ha^–1. This is not surprising given that P deficiency symptoms were observed during the early growth stages with deep placement of P and deep placement of P may delay P uptake until the rice roots reach the placement site.

The agronomic use efficiency of applied P (PUE) and apparent recovery of applied P (AR_P) increased across all deep placement treatments compared with broadcast and incorporation in both years (Table 8 ), except for the 56 kg P ha^–1 rate where there was no significant difference in PUE. The improvement in PUE and AR_P for deep-placed treatments clearly indicates better utilization and recovery of applied P fertilizer compared with the broadcast and incorporation of P.

Planting Spacing and Rice Response
The plant spacing in Treatment 18 was decreased from 20 by 20 cm to 20 by 10 cm, while maintaining the placement of briquettes at 40 by 40 cm. The closer spacing treatment was included to reduce the lag time for roots to contact P, particularly for the deep-placed P and for soils with low available P status. The grain yields were significantly higher in both years with 20 by 10 cm spacing compared with 20 by 20 cm plant spacing (Table 9 ). The straw yields, total P uptake, and total K uptake were also significantly different. The total N uptake in both years was not influenced by the plant spacing. The results confirm that the uptake of less mobile nutrient such as P and K uptake was significantly higher with closer spacing. The agronomic N use efficiency (Table 7), agronomic P use efficiency, and apparent recovery of applied fertilizer (Table 8) were significantly higher with closer plant spacing. The results also imply that deep placement of P fertilizer has potential benefits even in soils with very low P status when plant spacing is reduced.

	CONCLUSIONS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Deep placement of urea, urea+DAP, and urea+ DAP+MOP resulted in higher rice grain yield and in general higher uptake of nutrients compared with broadcast and incorporation of the fertilizers. Much of the yield benefits were attributed to deep placement of N. Similar or even higher grain yields were obtained with 40 kg ha^–1 less fertilizer N with deep placement than with broadcast application. This yield advantage is attributed to the reduced N loss and doubling of the fertilizer N recovery.

The effectiveness of deep placement in reducing N loss is reflected in the negligible amounts of ammoniacal-N in the floodwater. The deep placement of N–P briquettes was also very effective in reducing floodwater P content. The reduction in K content of the floodwater was significant though not as marked because of the high soil K status. Deep placement of the briquettes led to significant reduction in nutrient loads of N, P, and K in the floodwater. Deep placement of briquettes containing customized amounts of N, P, and K offers opportunities for low technology site-specific nutrient management for rice farmers.

Modification in plant spacing based on soil and climatic conditions could further enhance the efficiency of deep placement, particularly with respect to P response. Deep placement of N–P–K briquettes are being promoted in Bangladesh where apart from higher rice grain yields with less fertilizer, farmers are reporting labor savings from less weeding and split applications of N fertilizer (Roy and Nagy, 2002; Bowen et al., 2005). The economic gains (higher yield and less fertilizer) combined with labor savings was more than enough to offset the extra cost of briquette and labor required for deep placement. The deep placement technology also provides environmental benefits with extremely low nutrient loads in floodwater thus reducing potential runoff losses of N, P, and K and ammonia volatilization loss. One of the key constraints to widespread adoption of deep placement technology has been the lack of ready access to fertilizer briquettes or briquetting machines compared to conventional fertilizers.

	ACKNOWLEDGMENTS

 
The authors wish to thank IFDC's IFAD-funded ANMAT Project in Bangladesh for providing the N, N–P, and N–P–K briquettes for carrying out the study. They also acknowledge the help received from Mr. G. Yadav in carrying out the fieldwork and Drs. M. Wopereis and M. Elittä for their constructive comments on the manuscript.

All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

• Bowen, W.T., R.B. Diamond, U. Singh, and T.P. Thompson. 2005. Farmer and environmental benefits derived from deep placement of urea briquettes for flooded rice in Bangladesh. p. 71–76. In Zhaoliang Zhu et al. (ed.) 3rd Int. Nitrogen Conf., Contributed Papers, Inst. of Soil Science, Nanjing, China. 12–16 Oct. 2004. Science Press USA, Monmouth Junction, NJ.
• Bremner, J.M. 1960. Determination of nitrogen in soil by the Kjeldahl method. J. Agric. Sci. 55:11–33.
• Bremner, J.M., and D.R. Keeney. 1966. Determination and isotope analysis of different forms of nitrogen in soils. 3. Exchangeable ammonium, nitrate and nitrite by extraction distillation method. Soil Sci. Soc. Am. Proc. 30:577–582.
• Daftardar, S.Y., and N.K. Savant. 1995. Evaluation of environmentally friendly fertilizer management for rainfed lowland rice on tribal farmers' fields in India. p. 173–186. In Fragile lives in fragile ecosystems. Proc. of the Int. Rice Res. Conf., Int. Rice Res. Inst., Manila, the Philippines. 13–17 Feb. 1995. Int. Rice Res. Inst., Los Baños, Laguna, the Philippines.
• Day, P.R. 1965. Particle fractionation and particle size analysis. p. 545–567. In A.L. Page et al. (ed.) Methods of soil analysis. Part 2: Chemical and microbiological properties. ASA and SSSA, Madison, WI.
• Fillery, I.R.P., J.R. Simpson, and S.K. De Datta. 1984. Influence of field environment and fertilizer management on ammonia loss from flooded rice. Soil Sci. Soc. Am. J. 48:914–920.[Abstract/Free Full Text]
• Fillery, I.R.P., and P.L.G. Vlek. 1986. Reappraisal of the significance of ammonia volatilization as an N loss mechanism in flooded rice fields. Fert. Res. 9:79–98.
• Freney, J.R., O.T. Denmead, I. Watanabe, and E.T. Craswell. 1981. Ammonia and nitrous oxide losses following application of ammonium sulfate to flooded rice. Aust. J. Agric. Res. 32:37–45.[Web of Science]
• Godwin, D.C., and U. Singh. 1998. Nitrogen balance and crop response to nitrogen in upland and lowland cropping systems. p. 55–78. In G.Y. Tsuji et al.(ed.) Understanding options for agricultural production. Kluwer Academic Publ., Dordrecht, the Netherlands.
• Knudsen, D., G.A. Peterson, and P.F. Pratt. 1982. Lithium, sodium, and potassium. p. 225–246. In A.L. Page et al. (ed.) Methods of soil analysis, Part 2: Chemical and microbiological properties. ASA and SSSA, Madison, WI.
• Misra, C., B.C. Mohanty, B.S. Das, and N.K. Savant. 1995. Relationship between some selected soil properties and yield of transplanted rice fertilized with urea briquettes. Oryza 32:178–183.
• Mohanty, S.K., U. Singh, V. Balasubramanian, and K.P. Jha. 1999. Nitrogen deep-placement technologies for productivity, profitability, and environmental quality of rainfed lowland rice systems. Nutr. Cycl. Agroecosyst. 53:43–57.
• Nelson, D.W., and L.E. Sommers. 1996. Total carbon, organic carbon, and organic matter. p. 961–1010. In D.L. Sparks (ed.) Methods of soil analysis, Part 3: Chemical methods. SSSA Book Ser. 5. SSSA, Madison, WI.
• Olsen, S.R., C.V. Cole, F.S. Watanabe, and L.A. Dean. 1954. Estimation of available phosphorus in soils extracted with sodium bicarbonate. Circ. 1954:939. USDA, Washington, DC.
• Olsen, S.R., and L.E. Sommers. 1982. Phosphorus. p. 403–430. In A.L. Page et al.(ed.) Methods of soil analysis. Part 2: Chemical and microbiological properties. ASA and SSSA, Madison, WI.
• Patil, S.K., R.O. Das, V.N. Mishra, V.P. Singh, and U. Singh. 1998. Improving the use of residual nutrients by rice after a legume in the rainfed lowlands of Eastern India. p. 109–126. In J.K. Ladha et al. (ed.) Rainfed lowland rice: Advances in nutrient management research. Proc. of the Int. Workshop on Nutrient Res. in Rainfed Lowlands, Ubon Ratchatani, Thailand. 12–15 Oct. 1998. Int. Rice Res. Inst., Manila, the Philippines.
• Roy, R.N., and J.G. Nagy. 2002. Adapting Nutrient Management Technologies (ANMAT): Participatory evaluation, adaptation, and adoption of environmentally-friendly nutrient management technologies for resource poor farmers. External Review Report to IFAD Technical Assistance Grant 444-IFDC. IFDC, Muscle Shoals, AL.
• Samson, M.I., R.J. Buresh, and S.K. De Datta. 1987. Use of floodwater urea and ammonium to assess nitrogen transformations in lowland rice fields. J. Indian Agric. Res. Inst. Post-Graduate School 10(2):18–26.
• Savant, N.K., and P.J. Stangel. 1990. Deep placement of urea supergranules in transplanted rice: Principles and practices. Fert. Res. 25:1–83.
• Savant, N.K., and P.J. Stangel. 1998. Urea briquettes containing diammonium phosphate: A potential new NP fertilizer for transplanted rice. Nutr. Cycl. Agroecosyst. 51:85–94.
• Singh, U., K.G. Cassman, J.K. Ladha, and K.F. Bronson. 1995. Innovative nitrogen management strategies for lowland rice systems. p. 229–254. In Fragile lives in fragile ecosystems. Proc. of the Int. Rice Res. Conf. Int. Rice Res. Inst., Manila, the Philippines. 13–17 Feb. 1995. Int. Rice Res. Inst., Los Baños, Laguna, the Philippines.
• Srivastava, M.S., and E.M. Carter. 1983. Applied multivariate statistics. North-Holland, New York. p. 96–133.
• Thompson, T.P. 1992. Some sociological dimensions of technology for rice production in Bangladesh. J. Rural Dev. 22(2):1–28.
• Tomar, N.S., P. Singh, and L.V.S. Rao. 2004. Stability for yield in shallow water rice (Oryza sativa L.) under rainfed conditions. Indian J. Dryland Agric. Res. Develop. 19(2):123–125.
• Wetselaar, R., N. Sri Mulyani, and Hadiwahyono, J. Prawirasumantri, and A.M. Damdam. 1985. Deep-point placed urea in a flooded soil: Research results in West Java. p. 29–36. In P.J. Stangel et al. (ed.) Proc. of a Workshop on Urea Deep Placement Technology, Bogor, Indonesia. September 1984. Spec. Publ. SP-6. IFDC, Muscle Shoals, AL.

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Kapoor, V. Articles by Diamond, R. Search for Related Content PubMed Articles by Kapoor, V. Articles by Diamond, R. Agricola Articles by Kapoor, V. Articles by Diamond, R. Related Collections Rice Other Crop Management Best Management Practices Nutrients Nutrient Management