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Soil mineral nitrogen concentration within cycles of flood irrigation: Effect of rice stubble and fertilization management
Soil Bid Biochem.Vol. 18,No. 2. pp. 173-178,1986 Printed in Great Britain. All rights reserved
Copyright
6
0038.0717/86 $3.00+0.00 1986 Pergamon Press Ltd
SOIL MINERAL NITROGEN CONCENTRATION WITHIN CYCLES OF FLOOD IRRIGATION: EFFECT OF RICE STUBBLE AND FERTILIZATION MANAGEMENT P. E. BACON NSW Department
of Agriculture,
Agricultural
Institute,
Yanco,
NSW 2703, Australia
and J. W. MCGARITY, Department
of Agronomy
E. H. HOULT
and Soil Science, University
and
D. ALTER
of New England,
Armidale,
NSW 2351, Australia
(Accepted 13 September 1985)
Summary-Two field experiments using macro (3.5 x 12 m) plots and ‘5N-labelled fertilizer on micro (155 mm internal diameter) plots were undertaken to measure the effects of rice (Oryza satiua L.) stubble management and nitrogen fertilizer strategies on N transformations within a series of intermittent flood irrigations. Nitrate concentration fell by 90% during each flooding, and analysis of 15N micro plots showed the loss was due to denitrification rather than leaching. Over 52% of the 15N was lost. Apparent loss over four irrigations from macro plots receiving 60 kg urea-N ha-’ was 37 kg N ha-’ while unfertilized plots lost 19 kg N ha-‘. Stubble incorporation reduced nitrate accumulation rate and increased immobilization, thereby reducing denitrification losses by 23%. Nitrate concentration in the O-100 mm soil layer increased after the soil water content fell below field capacity during the drying portion of each cycle, but the net nitrification rate fell with increasing number of cycles. Ammonium content in the top 100mm of soil fell from 35 kgN ha-’ to 3 kgN haa’ over four irrigations. This fall was ascribed to the combined effects of nitrification and immobilization. Immobilization was greatest on plots where large quantities of rice stubble had been incorporated, and over 50% of the applied 15N was retained in the soil on these plots compared with 40% (SED = 3.5%) on plots where stubble had been burnt. We conclude that the poor response of rice to fertilization at sowing is due to a combination of denitrification and immobilization of applied nitrogen during cycles of wetting and drying prior to permanent flood.
INTRODUCTION Rice crops in temperate regions are a dry seedbed then given 2-4 short
often
sown
papers suggest that a sequence of nitrification then denitrification within each irrigation cycle was responsible for low mineral N availability at later growth stages. However, neither study had sufficient samplings to provide an insight into the importance of various N transformations such as immobilization and denitrification. Sampling intervals corresponding to those required for measureable changes in microbial activity are necessary to detect the rapid fluctuations in mineral N concentrations which can occur within individual irrigation cycles (Bacon and Davey, 1982). In the experiments reported here we examined the effects of nitrogen and stubble management techniques on fluctuations in soil mineral N concentrations within individual flood irrigation cycles. A study using “N was carried out to relate these fluctuations to various nitrogen transformations such as denitrification, immobilization, leaching and plant uptake. The study was part of a programme aimed at maximizing nitrogen fertilizer use efficiency under intensive rice-based cropping systems.
into
flood irrigations before permanent flooding when the crop is 150 mm high. Nitrogen fertilizer is sometimes applied at sowing in order to achieve rapid early growth (McDonald, 1979), even though nitrogen application at this time often has little effect on final yield (Bacon, 1982, 1985; Brandon et al., 1983). Several field studies (Strickland, 1969; Reid and Waring, 1979) show that soil mineral N levels fall between rice sowing and permanent flood. Reid and Waring (1979) found that soil ammonium concentration on plots receiving 120 kgNH,-N ha-’ fell from 145 to 44 kg N ha-’ following an average of 4 irrigations in a 34-day period. Nitrate concentration increased from 1 to 14 kg N ha-’ during the same period, indicating that some nitrification had occurred. The sampling interval used in the experiment was so large that it was not possible to identify changes in soil mineral N concentrations within individual irrigations. Strickland (1969) also took very few samples between sowing and permanent flood, but concluded that “nearly all of ammonium N applied as fertilizer at sowing has nitrified in the moist soil conditions prevailing before flooding and is lost within four weeks of flooding”. Both these
MATERIALS AND METHODS
Site conditions and experimental technique
The experiments were conducted at the Agricultural Institute, Yanco, Australia. The soil is described 173
174
P. E. BACON
as a Birganbigil clay loam (Van Dijk, 1961) one of the transitional red brown earths (Dr 2.22, Northtote, 1979) or Typic Paleustalfs (Soil Survey Staff, 1975) and typical of major rice growing areas of New South Wales. The A horizon (O-100 mm) had a pH of 5.3 (I : 5 soil: water), a bulk density of 1.4 and contained 1.2% organic C, 0.1% N and IO pg available Pgsoill’ (Bray and Kurtz. 1945). At -0.03 MPa the soil contained 24.2% moisture, while at - 1.5 MPa it contained 12.2% moisture. There was a marked change in both colour and texture between the surface and the B horizon. The B horizon was a dense, impermeable, medium clay, with a saturated hydraulic conductivity of 0.4 mm day-’ (Van der Lelij and Talsma, 1978) making it an ideal soil for rice growing. The low hydraulic conductivity meant there was very little water movement below the A horizon within individual irrigation cycles and any change in nitrate concentration reflected biological transformations rather than simply redistribution of nitrate within the profile (Bacon and Davey, 1982). Also, change in soil water content as these soils dry after irrigation is largely due to evaporation rather than deep percolation. A rice crop (Oryza suriva L. cv. Inga) was sown in 24 3.4 x 12 m plots on I November 1979. Half the plots received 100 kg N haa’ as urea just prior to permanent flood, while the other half were unfertilized. This fertilizer application produced an increase in above-ground rice stubble from 11.5 to 16.1 t ha- ‘_ In the following season these plots (hereafter referred to as high and low stubble treatments) were used in a factorial experiment involving the high and low levels of stubble from the previous crop, three stubble management techniques and two levels of N fertilization (O-60 kg urea-N) applied to the second rice crop (Table I). There were two replicates of this 2 x 3 x 2 factorial design. The second crop was sown on 10 November and appropriate plots fertilized immediately before the first irrigation. The crop then received three more flood irrigations before permanent flooding. In another experiment rice cv. Inga was sown on 26 October 1983 into an area which had grown rice crops in three previous summers. On four plots, stubble from each crop had been burnt, while on another four, stubble had been incorporated each year. In 1983 stubble was incorporated by rotary hoe on the four stubble incorporation plots on I3 SepTable N
applied
previous cr0p (kg N ha
0
I. Treatments
et Ul.
tember. while the other four plots were burnt on I I October. Immediately before the first irrigation on 27 October, one rigid plastic pressure pipe I55 mm i.d., 330 mm long was driven 320 mm into the soil in the centre of each plot. Urea powder equivalent to 100 kg N ha ’ and containing 5% “N was sprinkled on the soil surface of each pipe. Four rice seedlings were established in each pipe. Weeds were removed by hand as soon as they cmergcd and returned to the soil surface. The plots were food irrigated according to farmers’ usual practice on 27 October, 4 and 14 November. The flood irrigations were brief, and the water shallow., It was therefore unlikely that significant quantities of “N would diffuse out of the pressure pipe. Additionally unpublished data of the authors shows there is no measurable increase in the percentage of “N in soil or plants surrounding microplots similar to those used in this experiment. Sampling
and anal~~sis
In the first experiment six soil cores each 50 mm dia. were collected from the O-l 50 mm layer of each plot at each of 35 sampling times. The cores were extruded onto a table in the field and the O-100 mm layers were sectioned off for analysis. The base of the 100 mm sample always contained a small amount of the B horizon. The plastic bag containing the sample was then mixed by kneading vigorously and a portion removed for soil moisture content determination. Another sub-sample containing the equivalent of approximately 20g of dry soil was added to 250 ml bottles containing 200 ml 2 M KCI plus 5 pg phenylmercuric acetate mll’. These bottles were then vigorously shaken by hand and later mechanically shaken for at least 8 h prior to analysis for nitrate and ammonium. Nitrite was not considered important as previous studies in nearby sites showed NO,-N concentrations rarely exceeded 0.3 Llg g-’ (Bacon and Davey, 1982). Nitrate-N concentration was determined with a method developed from Best (1976). Copper sulphate (37.5 ml of a stock solution which contained 3.91 gCuS0,‘5Hz01 ’ H)O) was added to 0.5 ml Brij 35 surfactant and diluted to 500ml. One ml of this diluted solution was added to 20ml of KC1 extract plus I ml hydrazine sulphate solution (4 g I- ’ ) and 4 ml of buffer (135 g di-sodium tetraborate decahydrate + 15 g NaOH in 2 1 of hot distilled water). The solution was held for I5 min at 37’ C, then
used in the factorial
experiment N
to rice
Quantity
of
rice stubble
’)
(tha
b11.5
‘)
Stubble management technique
I. Stubble
applied
current lX1p
(kgNha 0
incorporated in Autumn (Early Inc.) 2. Stubble incorporated in Spring (Late Inc) 100
. 16.1
3. Stubble burned October then soil cultwated (Burn and Cultivate)
to rice
60
‘I
N cycling
under
intermittent
12 ml of colour reagent (200 ml concentrated HCl, 20g sulphanilamide, I g N-I-naphthyl ethylene diamine dihydrochloride and 2 ml Brij 35 in 2 1 water) was added. The mixture was then held at 37°C for 10 min and absorbance read at 520 nm. The limit of detection for this method was 0.5 /*g NO,-N gg’ oven dry soil. Ammonium-N concentration was determined using a method suggested by Pym and Milham (1976). Their method was modified to counter problems with precipitation of iron and manganese and interference of sulphides common in calorimetric determination of ammonium in rice soils. One ml of KC1 extract was added to 1 ml of ZnSO, solution (43.98 g ZnSO, 1-l of water) plus 36ml water and the mixture shaken. Six ml of sodium sahcylate solution (21.2 g NaOH plus 73.2 salicyhc acid dissolved in 900 ml H,O, cooled, then 0.6 g sodium nitroprusside added, solution diluted to 1 I) followed immediately by 6ml of dichloroisocyanurate solution (120 g NaOH dissolved in 900 ml H,O, cooled, then 2.5 g dichloroisocyanurate added and the solution diluted with H,O to 1 1). The resulting solution was immediately capped with an airtight seal and shaken. Absorbance was read at 650 nm after 15 min in the dark at 27°C. Both nitrate and ammonium concentrations are expressed as pg N g-’ of oven dry soil. In the second experiment rice plants including roots were harvested from the pipes after the third irrigation and the adhering soil gently removed. The plants were dried to constant weight at 70°C and total N uptake determined by macroKjeldah1 digestion using the sahcylic acid-sodium thiosulphate method to include nitrate-N (Bremner and Mulvaney, 1982). Immediately after plant harvest the pipes were dug out and all of the soil collected then dried at 60°C. Soil cores, 50 mm i.d. 750 mm long, were taken from the centre of each hole. These were cut into increments corresponding to depths of 300-550, 55CL800, 800-1050 mm and dried at 60°C. All of the soil was ground to a fine powder prior to N and 15N determination. The methods recommended by Hauck (1982) were used to avoid 15N sample loss and cross contamination. The ‘“N ratio was determined by mass spectrometry.
irrigation
175
ment resulted in large air spaces between clods. The initial irrigation caused slaking, leading to increased bulk density. After this there were repeated cycles of rapid rise and gradual fall in soil water content during each irrigation (Fig. 1). Stubble level, fertilization and residue management practices did not influence soil water content. Nitrate-Experiment
1
Nitrate-N concentration changed significantly with sampling time (Fig. 1) and this change was negatively correlated with soil water content (r’ = -0.34, P < 0.01). The infiltration characteristics of the B horizon indicate that solute movement would be confined within the surface soil samples during this experiment. It is therefore reasonable to assume that change in nitrate concentration with change in soil water content could be attributed to microbial transformations such as nitrification, immobilization and denitrification. The average maximum NO,-N content before irrigation was 4.6/.~gg~‘, being 6.1 pgg-’ on fertilized plots (i.e. those that had received 60 kg N ha-’ at the sowing of the current rice crop) and 3.4pg g-’ on unfertilized plots. An average of 0.64 pg g-’ NO,-N was present after irrigation, with no difference between fertilized and unfertilized plots. Thus each irrigation reduced nitrate concentration by almost 90%. Minimum nitrate concentrations occurred 24-29 h after the beginning of irrigation and significant increases in nitrate concentration were not apparent for up to 120 h after irrigation. This coincided with a fall in soil water content below field capacity (Fig. 1). Net nitrification rate fell during subsequent cycles of wetting and drying (Fig. 1). In the first two cycles,
RESULTS AND DISCUSSION
Soil moisture-Experiment
I
Soil water content varied according to time of sampling within irrigation cycles (Fig. 1). Field capacity was exceeded for an average of 61 h each cycle, with a film of free water on the soil surface for 24-30 h per cycle. The warm, dry weather resulted in rapid soil drying, and the soil water content approached permanent wilting point within 7 days of irrigation. The initial irrigation occurred within a few hours of topdressing, aiding the movement of urea into the profile and making ammonia volatilization unlikely (Ho& and Bacon, 1984). The maximum moisture content recorded in the first two cycles was significantly higher than that recorded later in the experiment, because cultivation prior to the experi-
0
2fO
435 Time
660
640
(h)
Fig. 1. Change in ammonium-N, nitrate-N concentration (pgg-‘) and soil water content (gg-‘) in the surface 1OOmm of soil during treatments.
5 flood irrigations. Mean ? = start of irrigation.
of all
176
P. E. Table
2. Effect of fertilizer,
Stubble management Early Inc. Late Inc. BW” Average
et ai
stubble management and number accumulation in exueriment I
N applied at sowing (kgNha ‘) 60 0 60 0 60 0 60 0
BACON
Net NO,-N (figg ‘) accumulation per cycle” Number of drying cycles ~~ I 2 3 4 9.2 2.6 8.2 2.3 10.6 5.1 9.0 2.9
5.1 3.6 7.6 2.4 7.6 4.2 6.7 3.2
5.8 1.7 5.4 4.2 4.8 4.0 4.0 3.1
2.5 0.7 I.0 0.8 5.3 2.1 3.0 1.1
of irrigation
cycles on nitrate
Maximum NO,-N accumulation rat-? (pgg-‘day-‘) Number of drying cycles I
2
3
4
3.17 0.53 2.82 I .06 3.65 2.24 2.98 0.83
I .39 2.15 2.67 2.53 5.10 2.42 I .90 2.42
1.85 2.50 I .80 3.12 I .63 3.12 I .09 2.32
1.37 0.71 0.55 0.35 2.76 1.30 I.16 0.78
“Calculated as maximum NO,-N pg g ~’ less mmimum NO,-N for each treatment. bCalculated as the maximum net increase in NO,-N during any 24 h. Maximum nitrate accumulation rate usually occurred as the soil water content capacity.
nitrate accumulated at up to 5 pg N03-N gg’ d-’ on fertilized plots (Table 2). During the last two cycles, increases of less than 1 pg gg’ day-’ were common. The net quantity of nitrate which disappeared during the five irrigations (calculated as NO,-N loss = NO,-N pg g-’ before irrigation less NOs-N after irrigation) was 26.7 pg NO,-N gg’ from fertilized plots and 13.6 pgg-’ from unfertilized plots, or 37 and 19 kg N ha-’ from fertilized and unfertilized plots respectively. Mean nitrate-N concentrations were similar for both stubble incorporation treatments and were significantly lower than those found under the burnt plots (early incorporated = 2.05, late incorporated = 2.20, burn and cultivated = 3.23 pg gg’, LSD 5% = 0.23 pg NOI-N gg’). Figure 2 shows that this difference resulted from higher nitrate accumulation rates on burnt plots as the soil dried out. Nitrate accumulated most rapidly on the burn plots which had just received 60 kg N ha-‘; prior to
t
t
t
I
I
I
I
I
I
0
240
660
640
435
t
Time(h)
Fig. 2. Effect of stubble management of nitrate-N (pgg-’ 0-100mm) during 5 irrigations. Mean of all N rates and stubble levels.
fell below field
irrigation these plots had an average of 8 pg NO,-N g-‘, while recently fertilized plots where stubble had been incorporated in autumn contained 5.1 pgNO,-N g-‘. The average net decrease in NOj-N per irrigation under the fertilized burn plots was more than 7pgg-‘, while under the stubble incorporation plots it was 4.7 pg gg ‘. Over the five irrigation cycles this was equivalent to 49 and 33 kg N ha-’ respectively. The lower nitrate concentrations in fertilized stubble incorporation plots reduced nitrate disappearance by 33% compared with the burn treatment. This probably reflected increased immobilization due to rice stubble incorporation. Stubble management also influenced nitrate N accumulation on plots which had not been fertilized immediately before the current crop. Nitrate concentration on unfertilized burnt plots just prior to the first, second and third irrigations was 6.2, 4.0 and 4.4pgg-’ respectively (LSD 5% = 1.96), while on the early incorporation or late incorporation plots they were 2.7, 1.5 and 2.3 and 4.1, 1.4 and 2.0 pg g ’ respectively. Unfertilized plots had an average postirrigation N03-N concentration of 0.5 pg gg ‘, indicating a nitrate loss over the first three irrigations of 18.3 and 7 kgN ha-’ for the unfertilized burnt and unfertilized stubble incorporation plots respectively. Average nitrate loss during the following two irrigations was equivalent to 7 kgN ha-’ on all unfertilized stubble management treatments. These results suggest that stubble incorporation substantially reduced net nitrate accumulation and consequently lowered the potential for subsequent denitrification on both fertilized and unfertilized plots. Fertilization immediately before irrigation increased apparent nitrogen loss from burnt plots by 25 kg N ha-’ or 42% of the applied nitrogen. Apparent loss of fertilizer from stubble incorporation plots was equivalent to 19 kg N ha-’ or 32% of applied N. The most likely reason for less nitrate accumulation on stubble incorporation plots would be increased uptake of ammonium by the heterotrophic microflora and consequent decrease in the supply of ammonium to the nitrifiers. This effect was greatest on plots where large quantities of stubble were buried. On these plots average nitrate concentration was significantly less than on plots with lower levels
177
N cycling under intermittent irrigation
I
’I
435 Time(h)
Fig. 3. Effect of fertilization and irrigation on nitrate-N and ammonium-N concentration (pg g-’ C-100 mm, expressed as the difference between fertilized and unfertilized plots).
of stubble (1.93 compared 5% = 0.33 pg N03-N g-l).
with
Ammonium-N-Experiment
1
2.32 pgg-‘,
LSD
Ammonium-N content fell with time. and the average concentrations during the four cycles were 10.7, 6.2, 3.6 and 2.6pgNH,-Ng-’ (Fig. 1). Ammonium was positively correlated concentration (r’ = 0.28, P < 0.01) with soil water content, but this correlation was largely due to urea hydrolysis being completed within the first irrigation. This resulted in relatively high ammonium concentrations on recently fertilized plots during the wet portion of the first irrigation cycle (Fig. 3). Fertilization immediately before the first irrigation increased averaged NH,-N concentration from 2.9 to 9.3 pg g-’ (LSD 5% = 0.51 pg gg’), but its effect was greatest in the early parts of the experiment, and there were no significant differences due to fertilization after the fourth irrigation (Fig. 3). During the first irrigation, ammonium content on fertilized plots rose from 7.5 to a maximum of 24.6 pg NH,-N g-l (LSD 5% = 3.02~gg~‘) 52 h after irrigation had commenced. The increase above pre-irrigation concentration was higher on burnt plots (24.4 pgg-‘, LSD 5% = 5.3 pg g-‘) than on the residue incorporation plots (16.7 pg g-l) suggesting very rapid immobilization on plots where stubble had been buried. However, stubble level did not significantly influence ammonium concentration. fell by Average ammonium concentration 7.95 pgg-’ in the following 48 h, and during this period 7.4 pg g-’ of NO,-N accumulated. Soil water content at this time was just below field capacity and near the optimal range for nitrification (Schmidt, 1982). Between 165 and 211 h after start of irrigation concentration fell from 23.7 to ammonium 12.3 pg g-‘. There was no change in nitrate concen-
tration during this period, so the fall in ammonium concentration was ascribed to immobilization. There was a gradual fall in ammonium concentration with time (Fig. l), and on some occasions, for instance in the second and third cycles, the fall was accompanied by a rise in nitrate, indicating that both immobilization and nitrification were occurring. These two processes combined to reduce ammonium concentration from a maximum of 35 kg N ha-’ during the first irrigation to 3 kg N ha-’ during the fifth irrigation. Plant N uptake at permanent flood ranged from 3 kg N ha-’ on unfertilized plots to 5 kg N ha-’ on plots receiving 60 kgN ha-’ at sowing. Therefore plant N uptake had little effect on soil mineral N concentration. The experiment above demonstrated that nitrate concentration varied in a cyclical fashion within each irrigation cycle. The fall in nitrate concentration during irrigation was interpreted as being due to denitrification, while the rise in concentration was due to nitrification following improved aeration as the soil dried out. The cyclic increase then decrease in nitrate was accompanied by a gradual fall in ammonium concentration suggesting a decline in the soil’s ability to supply mineral nitrogen. 15N stud] Soil sampling after three irrigations showed that 45% of the applied nitrogen was still present in the top 300 mm of soil. In this period rice seedlings accumulated only 1.5% of applied N (Table 3). Less than 2% had been leached beyond 300 mm, demonstrating that leaching was unimportant in this soil. Volatilization of NH, was also unimportant (Hoult and Bacon, 1984). Mineral N concentration in the top 300mm was less than 5 pgg-‘, and was not significantly different on control plots, indicating that the bulk of the applied “N remaining in the soil had been immobilized. The unaccounted for N must have been lost in the gaseous form, presumably by denitrification. Reddy and Patrick (1976) also found extensive immobilization and denitrification in a laboratory study of flooding and drying cycles. Labelled fertilizer retention in the soil was 23% greater under the stubble retention plots, indicating that stubble incorporation increased the extent of immobilization thereby reducing denitrification losses. Incorporating large quantities of rice stubble apparently increased immobilization and reduced denitrification. Craswell (1978) also found increased immobilization and reduced dentrification when straw was incorporated. The ultimate importance of this immobilized N would depend on the subsequent
Table
3. Distribution
three
flood
of isotopically
irrigations
after
enriched
application Stubble BurtI %
Plant Soil
O-300
mm
39.5
and
soil
ha ~’
management Incorporate
of “N 1.25
SED 0.26
49.5
3.5
300-550
mm
I .Oh
0.9
0.3
550-800
mm
0.82
0.56
0.3
0.06
0.12
0.13
800-1050 N accounted
N in plant 100 kg ~rea-‘~N
distribution
1.46 depth
of
for
mm
51.
I
47.7
178
P. E.
BACON
conditions influencing N mineralization and plant utilization. We conclude that the poor response to N applied to rice at sowing was due to both immobilization and denitrification which combined to reduce fertilizer availability. We suggest that delayed N application until just prior to permanent flooding would reduce the opportunity for N losses and additionally would result in N being applied at a stage of growth when the rice crop
is capable
of utilizing
the
fertilizer.
Acknowledgements-We gratefully acknowledge the financial assistance of the Irrigation Research and Extension Committee. We appreciate the skilled laboratory assistance of R. Stacy. The mass spectrometric analysis was carried out by Mr S. Stachiw, courtesy of Dr .I. Nolan, University of New England. The senior author acknowledges the assistance of his research directors in enabling this study to be carried out as part of his Ph.D. programme.
el a/.
D. R. Keeney, Eds). Agronomy No. 9 Part 2. 2nd edn. pp. 5955624. American Society of Agronomy, Madison. Wisconsin. Craswell E. T. (1978) Some factors influencmg denitrification and nitrogen immobilisation in a clay soil. Soil Biology & Biochemistry 10, 241 -245. Hauck R. D. (1982) Nitrogen--isotope ratio analysis. In Methods of Soil Analysis (A. L. Page, R. H. Miller and D. R. Keeney, Eds), Agronomy No 9, Part 2, 2nd edn, pp. 711-734. American Society of Agronomy. Madison. Wisconsin. Houh E. H. and Bacon P. E. (1984) N volatilization losses from an Australian rice bay. Proceedings of the National Soils Conference, Brisbane. p. 386. McDonald D. J. (1979) Rice. In Australian Field Crop.\ 2 (J. V. Lovett and A. Lazenby. Eds), pp. 70 94. Angus & Robertson, London. Northcote K. H. (1979) A Far&al Key ,fbr rhe Recognilion qf Australian Soils. 2nd edn. Rellim, Adelaide. Pym R. V. E. and Milham P. (1976) Selectivity of reaction among chlorine, ammonia and salicylate for determination of ammonia. Analyrical Chemistry 48, 1413-1415.
Reddy K. R. and Patrick W. H. Jr (1976) Effect of frequent changes in aerobic and anaerobic conditions on redox potential and nitrogen loss in a flooded soil. Soil Biology
REFERENCES
Bacon P. E. (1982) The effects of land and fertilizer management techniques on rice productivity under intensive rotations. Proceedings of the 2nd Australian Agronomy Conference, Wagga, p. 328. Bacon P. E. (1985) The effect of nitrogen application time on Calrose rice growth and yield in south-eastern Austraha. Australian Journal of Experimental Agriculture and Animal
Husbandry
Society
of America
Journal
8, 491495.
tralian Journal of E.xperimenfal Husbandry 19, 732-738.
Agriculture
and Atlima/
Schmidt
E. L. (1982) Nitrification in soil. In Nirrogen in Soi1.c (F. J. Stevenson, Ed.), Agronomy 22. pp. 253-288. American Society of Agromony, Madison. Wisconsin. Soil Survey Staff (1975) Soil Taxonomy. Agricultural Handbook No. 436, USDA. U.S. Government Printing Office, Washington, DC. Strickland R. W. (1969) Fluctuations in available mineral nitrogen in a flooded rice soil on the sub coastal plains of the Adelaide River, N.T. Australian Journul of E.uperiAgricultural
25, 1X3-190.
Bacon P. E. and Davey B. G. (1982) Nutrient under trickle irrigation: II. Mineral nitrogen.
& Biochemistry
Reid R. E. and Waring S. A. (1979) Nitrogen transformations in a soil of the lower Burdekin, Queensland. I. Mineral nitrogen and redox potential under rice. Aus-
availability Soil Science
46, 987-993.
Best E. K. (1976) An automated method for determining nitrate nitrogen in soil extracts. Queensland Department of Primary Industry, Division of Plant Industry Bulletin No. 33. Brandon D. M., Laing T. R., Leonardo W. J. Jr. Rawls S M. and Simoneaux N. J. (1983) Timing of basal N fertilizer in relation to permanently flooding dry seeded rice in north-east Louisiana (a preliminary report). In 751i1 Annual Progress Report. Rice Research Station Louisiana Agricultural Experiment Station, pp. 109-l 15. Bray R. H. and Kurtz L. T. (1945) Determination of total, organic, and available forms of phosphorus in soils. Soil Science 59, 3945. Bremner J. M. and Mulvaney C. S. (1982) Nitrogen-total. In Methods of‘Soil Anulysis (A. L. Page, R. H. Miller and
mental
Agriculture
and Animal
Husbandry
9, 532 540.
Van Dijk D. C. (1961) Soils of the southern portion of the Murrumbidgee Irrigation Area. CSIRO Australia. Soils and Land Use Series No. 40. Van der Lelij A. and T&ma T. (1978) Infiltration and water movement in riverine plain soils used for rice growing. In The Hydrogeology of’ Ihe Riverine Plain of Sourh-East Australia (R. R. Storrier and 1. D. Kelly. Eds), pp. X9 98.
Australian Society of Soil Science Incorporated, Branch Symposium. Griffith, July 1977.
Riverina
Copyright
6
0038.0717/86 $3.00+0.00 1986 Pergamon Press Ltd
SOIL MINERAL NITROGEN CONCENTRATION WITHIN CYCLES OF FLOOD IRRIGATION: EFFECT OF RICE STUBBLE AND FERTILIZATION MANAGEMENT P. E. BACON NSW Department
of Agriculture,
Agricultural
Institute,
Yanco,
NSW 2703, Australia
and J. W. MCGARITY, Department
of Agronomy
E. H. HOULT
and Soil Science, University
and
D. ALTER
of New England,
Armidale,
NSW 2351, Australia
(Accepted 13 September 1985)
Summary-Two field experiments using macro (3.5 x 12 m) plots and ‘5N-labelled fertilizer on micro (155 mm internal diameter) plots were undertaken to measure the effects of rice (Oryza satiua L.) stubble management and nitrogen fertilizer strategies on N transformations within a series of intermittent flood irrigations. Nitrate concentration fell by 90% during each flooding, and analysis of 15N micro plots showed the loss was due to denitrification rather than leaching. Over 52% of the 15N was lost. Apparent loss over four irrigations from macro plots receiving 60 kg urea-N ha-’ was 37 kg N ha-’ while unfertilized plots lost 19 kg N ha-‘. Stubble incorporation reduced nitrate accumulation rate and increased immobilization, thereby reducing denitrification losses by 23%. Nitrate concentration in the O-100 mm soil layer increased after the soil water content fell below field capacity during the drying portion of each cycle, but the net nitrification rate fell with increasing number of cycles. Ammonium content in the top 100mm of soil fell from 35 kgN ha-’ to 3 kgN haa’ over four irrigations. This fall was ascribed to the combined effects of nitrification and immobilization. Immobilization was greatest on plots where large quantities of rice stubble had been incorporated, and over 50% of the applied 15N was retained in the soil on these plots compared with 40% (SED = 3.5%) on plots where stubble had been burnt. We conclude that the poor response of rice to fertilization at sowing is due to a combination of denitrification and immobilization of applied nitrogen during cycles of wetting and drying prior to permanent flood.
INTRODUCTION Rice crops in temperate regions are a dry seedbed then given 2-4 short
often
sown
papers suggest that a sequence of nitrification then denitrification within each irrigation cycle was responsible for low mineral N availability at later growth stages. However, neither study had sufficient samplings to provide an insight into the importance of various N transformations such as immobilization and denitrification. Sampling intervals corresponding to those required for measureable changes in microbial activity are necessary to detect the rapid fluctuations in mineral N concentrations which can occur within individual irrigation cycles (Bacon and Davey, 1982). In the experiments reported here we examined the effects of nitrogen and stubble management techniques on fluctuations in soil mineral N concentrations within individual flood irrigation cycles. A study using “N was carried out to relate these fluctuations to various nitrogen transformations such as denitrification, immobilization, leaching and plant uptake. The study was part of a programme aimed at maximizing nitrogen fertilizer use efficiency under intensive rice-based cropping systems.
into
flood irrigations before permanent flooding when the crop is 150 mm high. Nitrogen fertilizer is sometimes applied at sowing in order to achieve rapid early growth (McDonald, 1979), even though nitrogen application at this time often has little effect on final yield (Bacon, 1982, 1985; Brandon et al., 1983). Several field studies (Strickland, 1969; Reid and Waring, 1979) show that soil mineral N levels fall between rice sowing and permanent flood. Reid and Waring (1979) found that soil ammonium concentration on plots receiving 120 kgNH,-N ha-’ fell from 145 to 44 kg N ha-’ following an average of 4 irrigations in a 34-day period. Nitrate concentration increased from 1 to 14 kg N ha-’ during the same period, indicating that some nitrification had occurred. The sampling interval used in the experiment was so large that it was not possible to identify changes in soil mineral N concentrations within individual irrigations. Strickland (1969) also took very few samples between sowing and permanent flood, but concluded that “nearly all of ammonium N applied as fertilizer at sowing has nitrified in the moist soil conditions prevailing before flooding and is lost within four weeks of flooding”. Both these
MATERIALS AND METHODS
Site conditions and experimental technique
The experiments were conducted at the Agricultural Institute, Yanco, Australia. The soil is described 173
174
P. E. BACON
as a Birganbigil clay loam (Van Dijk, 1961) one of the transitional red brown earths (Dr 2.22, Northtote, 1979) or Typic Paleustalfs (Soil Survey Staff, 1975) and typical of major rice growing areas of New South Wales. The A horizon (O-100 mm) had a pH of 5.3 (I : 5 soil: water), a bulk density of 1.4 and contained 1.2% organic C, 0.1% N and IO pg available Pgsoill’ (Bray and Kurtz. 1945). At -0.03 MPa the soil contained 24.2% moisture, while at - 1.5 MPa it contained 12.2% moisture. There was a marked change in both colour and texture between the surface and the B horizon. The B horizon was a dense, impermeable, medium clay, with a saturated hydraulic conductivity of 0.4 mm day-’ (Van der Lelij and Talsma, 1978) making it an ideal soil for rice growing. The low hydraulic conductivity meant there was very little water movement below the A horizon within individual irrigation cycles and any change in nitrate concentration reflected biological transformations rather than simply redistribution of nitrate within the profile (Bacon and Davey, 1982). Also, change in soil water content as these soils dry after irrigation is largely due to evaporation rather than deep percolation. A rice crop (Oryza suriva L. cv. Inga) was sown in 24 3.4 x 12 m plots on I November 1979. Half the plots received 100 kg N haa’ as urea just prior to permanent flood, while the other half were unfertilized. This fertilizer application produced an increase in above-ground rice stubble from 11.5 to 16.1 t ha- ‘_ In the following season these plots (hereafter referred to as high and low stubble treatments) were used in a factorial experiment involving the high and low levels of stubble from the previous crop, three stubble management techniques and two levels of N fertilization (O-60 kg urea-N) applied to the second rice crop (Table I). There were two replicates of this 2 x 3 x 2 factorial design. The second crop was sown on 10 November and appropriate plots fertilized immediately before the first irrigation. The crop then received three more flood irrigations before permanent flooding. In another experiment rice cv. Inga was sown on 26 October 1983 into an area which had grown rice crops in three previous summers. On four plots, stubble from each crop had been burnt, while on another four, stubble had been incorporated each year. In 1983 stubble was incorporated by rotary hoe on the four stubble incorporation plots on I3 SepTable N
applied
previous cr0p (kg N ha
0
I. Treatments
et Ul.
tember. while the other four plots were burnt on I I October. Immediately before the first irrigation on 27 October, one rigid plastic pressure pipe I55 mm i.d., 330 mm long was driven 320 mm into the soil in the centre of each plot. Urea powder equivalent to 100 kg N ha ’ and containing 5% “N was sprinkled on the soil surface of each pipe. Four rice seedlings were established in each pipe. Weeds were removed by hand as soon as they cmergcd and returned to the soil surface. The plots were food irrigated according to farmers’ usual practice on 27 October, 4 and 14 November. The flood irrigations were brief, and the water shallow., It was therefore unlikely that significant quantities of “N would diffuse out of the pressure pipe. Additionally unpublished data of the authors shows there is no measurable increase in the percentage of “N in soil or plants surrounding microplots similar to those used in this experiment. Sampling
and anal~~sis
In the first experiment six soil cores each 50 mm dia. were collected from the O-l 50 mm layer of each plot at each of 35 sampling times. The cores were extruded onto a table in the field and the O-100 mm layers were sectioned off for analysis. The base of the 100 mm sample always contained a small amount of the B horizon. The plastic bag containing the sample was then mixed by kneading vigorously and a portion removed for soil moisture content determination. Another sub-sample containing the equivalent of approximately 20g of dry soil was added to 250 ml bottles containing 200 ml 2 M KCI plus 5 pg phenylmercuric acetate mll’. These bottles were then vigorously shaken by hand and later mechanically shaken for at least 8 h prior to analysis for nitrate and ammonium. Nitrite was not considered important as previous studies in nearby sites showed NO,-N concentrations rarely exceeded 0.3 Llg g-’ (Bacon and Davey, 1982). Nitrate-N concentration was determined with a method developed from Best (1976). Copper sulphate (37.5 ml of a stock solution which contained 3.91 gCuS0,‘5Hz01 ’ H)O) was added to 0.5 ml Brij 35 surfactant and diluted to 500ml. One ml of this diluted solution was added to 20ml of KC1 extract plus I ml hydrazine sulphate solution (4 g I- ’ ) and 4 ml of buffer (135 g di-sodium tetraborate decahydrate + 15 g NaOH in 2 1 of hot distilled water). The solution was held for I5 min at 37’ C, then
used in the factorial
experiment N
to rice
Quantity
of
rice stubble
’)
(tha
b11.5
‘)
Stubble management technique
I. Stubble
applied
current lX1p
(kgNha 0
incorporated in Autumn (Early Inc.) 2. Stubble incorporated in Spring (Late Inc) 100
. 16.1
3. Stubble burned October then soil cultwated (Burn and Cultivate)
to rice
60
‘I
N cycling
under
intermittent
12 ml of colour reagent (200 ml concentrated HCl, 20g sulphanilamide, I g N-I-naphthyl ethylene diamine dihydrochloride and 2 ml Brij 35 in 2 1 water) was added. The mixture was then held at 37°C for 10 min and absorbance read at 520 nm. The limit of detection for this method was 0.5 /*g NO,-N gg’ oven dry soil. Ammonium-N concentration was determined using a method suggested by Pym and Milham (1976). Their method was modified to counter problems with precipitation of iron and manganese and interference of sulphides common in calorimetric determination of ammonium in rice soils. One ml of KC1 extract was added to 1 ml of ZnSO, solution (43.98 g ZnSO, 1-l of water) plus 36ml water and the mixture shaken. Six ml of sodium sahcylate solution (21.2 g NaOH plus 73.2 salicyhc acid dissolved in 900 ml H,O, cooled, then 0.6 g sodium nitroprusside added, solution diluted to 1 I) followed immediately by 6ml of dichloroisocyanurate solution (120 g NaOH dissolved in 900 ml H,O, cooled, then 2.5 g dichloroisocyanurate added and the solution diluted with H,O to 1 1). The resulting solution was immediately capped with an airtight seal and shaken. Absorbance was read at 650 nm after 15 min in the dark at 27°C. Both nitrate and ammonium concentrations are expressed as pg N g-’ of oven dry soil. In the second experiment rice plants including roots were harvested from the pipes after the third irrigation and the adhering soil gently removed. The plants were dried to constant weight at 70°C and total N uptake determined by macroKjeldah1 digestion using the sahcylic acid-sodium thiosulphate method to include nitrate-N (Bremner and Mulvaney, 1982). Immediately after plant harvest the pipes were dug out and all of the soil collected then dried at 60°C. Soil cores, 50 mm i.d. 750 mm long, were taken from the centre of each hole. These were cut into increments corresponding to depths of 300-550, 55CL800, 800-1050 mm and dried at 60°C. All of the soil was ground to a fine powder prior to N and 15N determination. The methods recommended by Hauck (1982) were used to avoid 15N sample loss and cross contamination. The ‘“N ratio was determined by mass spectrometry.
irrigation
175
ment resulted in large air spaces between clods. The initial irrigation caused slaking, leading to increased bulk density. After this there were repeated cycles of rapid rise and gradual fall in soil water content during each irrigation (Fig. 1). Stubble level, fertilization and residue management practices did not influence soil water content. Nitrate-Experiment
1
Nitrate-N concentration changed significantly with sampling time (Fig. 1) and this change was negatively correlated with soil water content (r’ = -0.34, P < 0.01). The infiltration characteristics of the B horizon indicate that solute movement would be confined within the surface soil samples during this experiment. It is therefore reasonable to assume that change in nitrate concentration with change in soil water content could be attributed to microbial transformations such as nitrification, immobilization and denitrification. The average maximum NO,-N content before irrigation was 4.6/.~gg~‘, being 6.1 pgg-’ on fertilized plots (i.e. those that had received 60 kg N ha-’ at the sowing of the current rice crop) and 3.4pg g-’ on unfertilized plots. An average of 0.64 pg g-’ NO,-N was present after irrigation, with no difference between fertilized and unfertilized plots. Thus each irrigation reduced nitrate concentration by almost 90%. Minimum nitrate concentrations occurred 24-29 h after the beginning of irrigation and significant increases in nitrate concentration were not apparent for up to 120 h after irrigation. This coincided with a fall in soil water content below field capacity (Fig. 1). Net nitrification rate fell during subsequent cycles of wetting and drying (Fig. 1). In the first two cycles,
RESULTS AND DISCUSSION
Soil moisture-Experiment
I
Soil water content varied according to time of sampling within irrigation cycles (Fig. 1). Field capacity was exceeded for an average of 61 h each cycle, with a film of free water on the soil surface for 24-30 h per cycle. The warm, dry weather resulted in rapid soil drying, and the soil water content approached permanent wilting point within 7 days of irrigation. The initial irrigation occurred within a few hours of topdressing, aiding the movement of urea into the profile and making ammonia volatilization unlikely (Ho& and Bacon, 1984). The maximum moisture content recorded in the first two cycles was significantly higher than that recorded later in the experiment, because cultivation prior to the experi-
0
2fO
435 Time
660
640
(h)
Fig. 1. Change in ammonium-N, nitrate-N concentration (pgg-‘) and soil water content (gg-‘) in the surface 1OOmm of soil during treatments.
5 flood irrigations. Mean ? = start of irrigation.
of all
176
P. E. Table
2. Effect of fertilizer,
Stubble management Early Inc. Late Inc. BW” Average
et ai
stubble management and number accumulation in exueriment I
N applied at sowing (kgNha ‘) 60 0 60 0 60 0 60 0
BACON
Net NO,-N (figg ‘) accumulation per cycle” Number of drying cycles ~~ I 2 3 4 9.2 2.6 8.2 2.3 10.6 5.1 9.0 2.9
5.1 3.6 7.6 2.4 7.6 4.2 6.7 3.2
5.8 1.7 5.4 4.2 4.8 4.0 4.0 3.1
2.5 0.7 I.0 0.8 5.3 2.1 3.0 1.1
of irrigation
cycles on nitrate
Maximum NO,-N accumulation rat-? (pgg-‘day-‘) Number of drying cycles I
2
3
4
3.17 0.53 2.82 I .06 3.65 2.24 2.98 0.83
I .39 2.15 2.67 2.53 5.10 2.42 I .90 2.42
1.85 2.50 I .80 3.12 I .63 3.12 I .09 2.32
1.37 0.71 0.55 0.35 2.76 1.30 I.16 0.78
“Calculated as maximum NO,-N pg g ~’ less mmimum NO,-N for each treatment. bCalculated as the maximum net increase in NO,-N during any 24 h. Maximum nitrate accumulation rate usually occurred as the soil water content capacity.
nitrate accumulated at up to 5 pg N03-N gg’ d-’ on fertilized plots (Table 2). During the last two cycles, increases of less than 1 pg gg’ day-’ were common. The net quantity of nitrate which disappeared during the five irrigations (calculated as NO,-N loss = NO,-N pg g-’ before irrigation less NOs-N after irrigation) was 26.7 pg NO,-N gg’ from fertilized plots and 13.6 pgg-’ from unfertilized plots, or 37 and 19 kg N ha-’ from fertilized and unfertilized plots respectively. Mean nitrate-N concentrations were similar for both stubble incorporation treatments and were significantly lower than those found under the burnt plots (early incorporated = 2.05, late incorporated = 2.20, burn and cultivated = 3.23 pg gg’, LSD 5% = 0.23 pg NOI-N gg’). Figure 2 shows that this difference resulted from higher nitrate accumulation rates on burnt plots as the soil dried out. Nitrate accumulated most rapidly on the burn plots which had just received 60 kg N ha-‘; prior to
t
t
t
I
I
I
I
I
I
0
240
660
640
435
t
Time(h)
Fig. 2. Effect of stubble management of nitrate-N (pgg-’ 0-100mm) during 5 irrigations. Mean of all N rates and stubble levels.
fell below field
irrigation these plots had an average of 8 pg NO,-N g-‘, while recently fertilized plots where stubble had been incorporated in autumn contained 5.1 pgNO,-N g-‘. The average net decrease in NOj-N per irrigation under the fertilized burn plots was more than 7pgg-‘, while under the stubble incorporation plots it was 4.7 pg gg ‘. Over the five irrigation cycles this was equivalent to 49 and 33 kg N ha-’ respectively. The lower nitrate concentrations in fertilized stubble incorporation plots reduced nitrate disappearance by 33% compared with the burn treatment. This probably reflected increased immobilization due to rice stubble incorporation. Stubble management also influenced nitrate N accumulation on plots which had not been fertilized immediately before the current crop. Nitrate concentration on unfertilized burnt plots just prior to the first, second and third irrigations was 6.2, 4.0 and 4.4pgg-’ respectively (LSD 5% = 1.96), while on the early incorporation or late incorporation plots they were 2.7, 1.5 and 2.3 and 4.1, 1.4 and 2.0 pg g ’ respectively. Unfertilized plots had an average postirrigation N03-N concentration of 0.5 pg gg ‘, indicating a nitrate loss over the first three irrigations of 18.3 and 7 kgN ha-’ for the unfertilized burnt and unfertilized stubble incorporation plots respectively. Average nitrate loss during the following two irrigations was equivalent to 7 kgN ha-’ on all unfertilized stubble management treatments. These results suggest that stubble incorporation substantially reduced net nitrate accumulation and consequently lowered the potential for subsequent denitrification on both fertilized and unfertilized plots. Fertilization immediately before irrigation increased apparent nitrogen loss from burnt plots by 25 kg N ha-’ or 42% of the applied nitrogen. Apparent loss of fertilizer from stubble incorporation plots was equivalent to 19 kg N ha-’ or 32% of applied N. The most likely reason for less nitrate accumulation on stubble incorporation plots would be increased uptake of ammonium by the heterotrophic microflora and consequent decrease in the supply of ammonium to the nitrifiers. This effect was greatest on plots where large quantities of stubble were buried. On these plots average nitrate concentration was significantly less than on plots with lower levels
177
N cycling under intermittent irrigation
I
’I
435 Time(h)
Fig. 3. Effect of fertilization and irrigation on nitrate-N and ammonium-N concentration (pg g-’ C-100 mm, expressed as the difference between fertilized and unfertilized plots).
of stubble (1.93 compared 5% = 0.33 pg N03-N g-l).
with
Ammonium-N-Experiment
1
2.32 pgg-‘,
LSD
Ammonium-N content fell with time. and the average concentrations during the four cycles were 10.7, 6.2, 3.6 and 2.6pgNH,-Ng-’ (Fig. 1). Ammonium was positively correlated concentration (r’ = 0.28, P < 0.01) with soil water content, but this correlation was largely due to urea hydrolysis being completed within the first irrigation. This resulted in relatively high ammonium concentrations on recently fertilized plots during the wet portion of the first irrigation cycle (Fig. 3). Fertilization immediately before the first irrigation increased averaged NH,-N concentration from 2.9 to 9.3 pg g-’ (LSD 5% = 0.51 pg gg’), but its effect was greatest in the early parts of the experiment, and there were no significant differences due to fertilization after the fourth irrigation (Fig. 3). During the first irrigation, ammonium content on fertilized plots rose from 7.5 to a maximum of 24.6 pg NH,-N g-l (LSD 5% = 3.02~gg~‘) 52 h after irrigation had commenced. The increase above pre-irrigation concentration was higher on burnt plots (24.4 pgg-‘, LSD 5% = 5.3 pg g-‘) than on the residue incorporation plots (16.7 pg g-l) suggesting very rapid immobilization on plots where stubble had been buried. However, stubble level did not significantly influence ammonium concentration. fell by Average ammonium concentration 7.95 pgg-’ in the following 48 h, and during this period 7.4 pg g-’ of NO,-N accumulated. Soil water content at this time was just below field capacity and near the optimal range for nitrification (Schmidt, 1982). Between 165 and 211 h after start of irrigation concentration fell from 23.7 to ammonium 12.3 pg g-‘. There was no change in nitrate concen-
tration during this period, so the fall in ammonium concentration was ascribed to immobilization. There was a gradual fall in ammonium concentration with time (Fig. l), and on some occasions, for instance in the second and third cycles, the fall was accompanied by a rise in nitrate, indicating that both immobilization and nitrification were occurring. These two processes combined to reduce ammonium concentration from a maximum of 35 kg N ha-’ during the first irrigation to 3 kg N ha-’ during the fifth irrigation. Plant N uptake at permanent flood ranged from 3 kg N ha-’ on unfertilized plots to 5 kg N ha-’ on plots receiving 60 kgN ha-’ at sowing. Therefore plant N uptake had little effect on soil mineral N concentration. The experiment above demonstrated that nitrate concentration varied in a cyclical fashion within each irrigation cycle. The fall in nitrate concentration during irrigation was interpreted as being due to denitrification, while the rise in concentration was due to nitrification following improved aeration as the soil dried out. The cyclic increase then decrease in nitrate was accompanied by a gradual fall in ammonium concentration suggesting a decline in the soil’s ability to supply mineral nitrogen. 15N stud] Soil sampling after three irrigations showed that 45% of the applied nitrogen was still present in the top 300 mm of soil. In this period rice seedlings accumulated only 1.5% of applied N (Table 3). Less than 2% had been leached beyond 300 mm, demonstrating that leaching was unimportant in this soil. Volatilization of NH, was also unimportant (Hoult and Bacon, 1984). Mineral N concentration in the top 300mm was less than 5 pgg-‘, and was not significantly different on control plots, indicating that the bulk of the applied “N remaining in the soil had been immobilized. The unaccounted for N must have been lost in the gaseous form, presumably by denitrification. Reddy and Patrick (1976) also found extensive immobilization and denitrification in a laboratory study of flooding and drying cycles. Labelled fertilizer retention in the soil was 23% greater under the stubble retention plots, indicating that stubble incorporation increased the extent of immobilization thereby reducing denitrification losses. Incorporating large quantities of rice stubble apparently increased immobilization and reduced denitrification. Craswell (1978) also found increased immobilization and reduced dentrification when straw was incorporated. The ultimate importance of this immobilized N would depend on the subsequent
Table
3. Distribution
three
flood
of isotopically
irrigations
after
enriched
application Stubble BurtI %
Plant Soil
O-300
mm
39.5
and
soil
ha ~’
management Incorporate
of “N 1.25
SED 0.26
49.5
3.5
300-550
mm
I .Oh
0.9
0.3
550-800
mm
0.82
0.56
0.3
0.06
0.12
0.13
800-1050 N accounted
N in plant 100 kg ~rea-‘~N
distribution
1.46 depth
of
for
mm
51.
I
47.7
178
P. E.
BACON
conditions influencing N mineralization and plant utilization. We conclude that the poor response to N applied to rice at sowing was due to both immobilization and denitrification which combined to reduce fertilizer availability. We suggest that delayed N application until just prior to permanent flooding would reduce the opportunity for N losses and additionally would result in N being applied at a stage of growth when the rice crop
is capable
of utilizing
the
fertilizer.
Acknowledgements-We gratefully acknowledge the financial assistance of the Irrigation Research and Extension Committee. We appreciate the skilled laboratory assistance of R. Stacy. The mass spectrometric analysis was carried out by Mr S. Stachiw, courtesy of Dr .I. Nolan, University of New England. The senior author acknowledges the assistance of his research directors in enabling this study to be carried out as part of his Ph.D. programme.
el a/.
D. R. Keeney, Eds). Agronomy No. 9 Part 2. 2nd edn. pp. 5955624. American Society of Agronomy, Madison. Wisconsin. Craswell E. T. (1978) Some factors influencmg denitrification and nitrogen immobilisation in a clay soil. Soil Biology & Biochemistry 10, 241 -245. Hauck R. D. (1982) Nitrogen--isotope ratio analysis. In Methods of Soil Analysis (A. L. Page, R. H. Miller and D. R. Keeney, Eds), Agronomy No 9, Part 2, 2nd edn, pp. 711-734. American Society of Agronomy. Madison. Wisconsin. Houh E. H. and Bacon P. E. (1984) N volatilization losses from an Australian rice bay. Proceedings of the National Soils Conference, Brisbane. p. 386. McDonald D. J. (1979) Rice. In Australian Field Crop.\ 2 (J. V. Lovett and A. Lazenby. Eds), pp. 70 94. Angus & Robertson, London. Northcote K. H. (1979) A Far&al Key ,fbr rhe Recognilion qf Australian Soils. 2nd edn. Rellim, Adelaide. Pym R. V. E. and Milham P. (1976) Selectivity of reaction among chlorine, ammonia and salicylate for determination of ammonia. Analyrical Chemistry 48, 1413-1415.
Reddy K. R. and Patrick W. H. Jr (1976) Effect of frequent changes in aerobic and anaerobic conditions on redox potential and nitrogen loss in a flooded soil. Soil Biology
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Bacon P. E. (1982) The effects of land and fertilizer management techniques on rice productivity under intensive rotations. Proceedings of the 2nd Australian Agronomy Conference, Wagga, p. 328. Bacon P. E. (1985) The effect of nitrogen application time on Calrose rice growth and yield in south-eastern Austraha. Australian Journal of Experimental Agriculture and Animal
Husbandry
Society
of America
Journal
8, 491495.
tralian Journal of E.xperimenfal Husbandry 19, 732-738.
Agriculture
and Atlima/
Schmidt
E. L. (1982) Nitrification in soil. In Nirrogen in Soi1.c (F. J. Stevenson, Ed.), Agronomy 22. pp. 253-288. American Society of Agromony, Madison. Wisconsin. Soil Survey Staff (1975) Soil Taxonomy. Agricultural Handbook No. 436, USDA. U.S. Government Printing Office, Washington, DC. Strickland R. W. (1969) Fluctuations in available mineral nitrogen in a flooded rice soil on the sub coastal plains of the Adelaide River, N.T. Australian Journul of E.uperiAgricultural
25, 1X3-190.
Bacon P. E. and Davey B. G. (1982) Nutrient under trickle irrigation: II. Mineral nitrogen.
& Biochemistry
Reid R. E. and Waring S. A. (1979) Nitrogen transformations in a soil of the lower Burdekin, Queensland. I. Mineral nitrogen and redox potential under rice. Aus-
availability Soil Science
46, 987-993.
Best E. K. (1976) An automated method for determining nitrate nitrogen in soil extracts. Queensland Department of Primary Industry, Division of Plant Industry Bulletin No. 33. Brandon D. M., Laing T. R., Leonardo W. J. Jr. Rawls S M. and Simoneaux N. J. (1983) Timing of basal N fertilizer in relation to permanently flooding dry seeded rice in north-east Louisiana (a preliminary report). In 751i1 Annual Progress Report. Rice Research Station Louisiana Agricultural Experiment Station, pp. 109-l 15. Bray R. H. and Kurtz L. T. (1945) Determination of total, organic, and available forms of phosphorus in soils. Soil Science 59, 3945. Bremner J. M. and Mulvaney C. S. (1982) Nitrogen-total. In Methods of‘Soil Anulysis (A. L. Page, R. H. Miller and
mental
Agriculture
and Animal
Husbandry
9, 532 540.
Van Dijk D. C. (1961) Soils of the southern portion of the Murrumbidgee Irrigation Area. CSIRO Australia. Soils and Land Use Series No. 40. Van der Lelij A. and T&ma T. (1978) Infiltration and water movement in riverine plain soils used for rice growing. In The Hydrogeology of’ Ihe Riverine Plain of Sourh-East Australia (R. R. Storrier and 1. D. Kelly. Eds), pp. X9 98.
Australian Society of Soil Science Incorporated, Branch Symposium. Griffith, July 1977.
Riverina