Nitrate accumulation under cropping in the Ferrosols of Far North Queensland wet tropics.
Recent fertiliser N mass-balance studies for the major cropping systems (sugarcane, banana, and pasture) in the wet-tropical Johnstone River Catchment (JRC) of Far North Queensland (FNQ) showed that 30-50% of the fertiliser N applied to Ferrosols leached below the crop root-zone ([is less than] 0.75 m) as nitrate (Moody et al. 1996; Prove and Moody 1997). The results also indicated an imbalance between the applied and recovered N, indicating the fate of the applied N was not fully accounted for. The amount of nitrate leaching below the crop root-zone may depend on the quantity and quality of the N fertiliser used, time and frequency of application, the crop grown and its duration, crop N-utilisation efficiency, rooting depth, rainfall, soil hydraulic characteristics, and management practices, such as differences in tillage, and trash retention/burning (for sugarcane). In general, the N fertiliser use in the major cropping systems in JRC is relatively high. The annual N fertiliser application rate for sugarcane in this region ranged from 100 to 200 kg/ha (Rasiah et al. 1999), 100 to 900 kg/ha for banana (Daniells 1995), and 20 to 500 kg/ha for grazed pasture (G. Sipson, pers. comm.). At a catchment scale, the quantity of nitrate leaching below the crop root-zone (30-50% of the applied N in case of some Ferrosols) and that unaccounted for in the mass-balance under high N fertiliser application rates may be very large. Therefore, quantitative information on the fate of this nitrate is essential to develop efficient N fertiliser management practices that will reduce input cost to growers and the environmental problems associated with high nitrate concentration in surface and groundwater bodies.
The nitrate leaching below the crop root-zone may be adsorbed onto soil, move laterally to discharge into streams and rivers, enter deep groundwater, and/or denitrify in the profile. Ferrosol profiles are deep, 1 to [is greater than] 10 m (Cotching 1995), and have high hydraulic conductivity (Bonell et al. 1983). These characteristics, in conjunction with undulating topography/landscape and high rainfall (3300 mm per year, 60-year average), provide conditions favourable for lateral flow and deep drainage (Hair 1990; Cotching 1995). Under these conditions, some of the nitrate leaching below the crop root-zone in JRC may enter streams, as lateral-flow, that discharge into the Great Barrier Reef (GBR). The GBR stretches along the mid-outer continental shelf of north-eastern Australia, and acts as a semi-enclosed lagoon. High nitrate concentrations in streams and estuaries favour algal blooms and eutrophication. Yellowlees (1991) reported a net export of nutrients to the GBR from agricultural land, including that from JRC, suggesting the environmental health of the GBR ecosystem may be affected by the fertiliser management practices adopted for cropping in FNQ.
Although the physical conditions (rainfall, deep profile, and conductivity) prevailing in the Ferrosols of the JRC are favourable for both vertical and lateral transport of nitrate, the anion adsorption and other chemical attributes of these soils may also determine the fate of the nitrate transported below the crop root-zone. Nitrate adsorption at anion exchange sites in the soil matrix has long been reported for several tropical soil types, including the Ferrosols (Singh and Kanehiro 1969; Black and Waring 1976a, 1976b, 1976c, 1979; Katou et al. 1996). The non-specific adsorption of nitrate and chloride anions results from coulombic attraction at the positively charged sites in soil minerals (Hingston et al. 1972). The 1:1 layer silicates (Schofield and Samson 1953; Quirk 1960; Fordham 1973), iron (Schofield 1949; Sumner 1963; Sumner and Reeve 1966) and aluminium (Deshpande et al. 1964; Tweneboah et al. 1967) oxide, and allophane (Wada and Harward 1974) minerals are capable of producing positively charged sites. The amount of nitrate adsorbed in soil depends on anion exchange capacity (AEC) (Kinjo and Pratt 1971a; Espinoza et al. 1975; Black and Waring 1976b), net negative charge, i.e. [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (Black and Waring 1976b), ionic strength of the soil bulk solution (Katou et al. 1996), nitrate concentration (Black and Waring 1976c), competition with other anions such as [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] or [Cl.sup.-] (Singh and Kanehiro 1969; Katou et al. 1996), [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (Black and Waring 1976b; Ishiguro et al. 1992), anionic composition of the soil solution (Kinjo and Pratt 1971a; Katou et al. 1996), cation exchange capacity (CEC) (Okumara and Wada 1983; Wong et al. 1990), and leaching (Black and Waring 1976b; Wong et al. 1990). The effects of these factors on nitrate retention have been measured in leaching column experiments using soil samples from the plough layer ([is less than] 20 cm), apart from the field data of Black and Waring (1976b).
To gather in situ information on the fate of the nitrate that has leached below the root-zones of major crops grown in the Ferrosols of JRC, we conducted a study to (i) verify whether the nitrate has accumulated in the Ferrosols profiles, and (ii) provide preliminary estimates of nitrate retention capacity.
Materials and methods
Soil cores to a depth of 10 m were taken from the JRC, 1634 [km.sup.2] in area and located approximately 17 [degrees] 30'S 145 [degrees] 50'E. The major streams in the JRC are the Johnstone and South Johnstone Rivers, both of which rise in the south-eastern section of the Atherton Tableland (Malanda elevation 740 m), pass through large areas of native rainforest in the midsections of the catchment, and then drain undulating lowlands and flood plains (Fig. 1). The rivers converge at Innisfail, where the Johnstone River estuary discharges into the GBR. Pristine rainforest covers ~52% of the catchment, pasture 28% (both dairy and beef), sugarcane 12%, and banana 6% (Prove and Moody 1997). Rainfall is typically summer dominant, with mean annual values of 1680 mm at Malanda in the upper catchment and 3500 mm at Innisfail on the coast.
Soil cores supporting long-term sugarcane and banana production were taken from different paddocks belonging to different growers in the JRC (Fig. 1). The cane-130 core was taken from the mid-section of a paddock, with a small gradient ([is less than] 3%) sloping east to west. The cane-118 core was taken from the toeslope position in a paddock that had a steep gradient (5-7%), sloping north to south and east to west towards the core location. Both paddocks have been under continuous sugarcane cultivation for more than 50 years and under a trash retention system for at least 10 years before coring. There were no creeks or drainage ditches in close vicinity to these paddocks. The soil core representing banana production was taken from the top shoulder position of a paddock, with a gentle slope ([is less than] 2%), and the core location was ~300 m away from a creek which carried both surface and lateral flow from the paddock for [is greater than] 6 months in a year. The lateral horizontal separation between the sugarcane sites was [is less than] 2 km and that between the banana and sugarcane sites was ~15 km. The core representing dairy pasture was taken from the mid-section of a pasture paddock with a steep slope (5-10%), at Milla Milla, which is ~25 km from the other sites. There was a small creek at the lower aspect of the paddock and very few perennial trees in the paddock. The dominant pasture species was setaria grass (Setaria anceps). The rainforest core was taken from a power grid clearing in a Natural Heritage Reservation located along the Palmerstone highway and ~35 km from Innisfail. The core location was ~20 m from undisturbed rainforest and had a slope 1-2%. There were no creeks in close vicinity.
[Figure 1 ILLUSTRATION OMITTED]
Fertiliser management history at the sites.
Urea was usually applied at planting, during July-September (50 kg N/ha), with superphosphate (60 kg/ha), and muriate of potash (150 kg K/ha). Urea was again side-dressed at a rate of 100-120 kg N/ha in October-November. After harvesting in June-September, the ratoon crop received 165 kg N/ha as urea and 180 kg K/ha as muriate of potash. This fertiliser management was repeated for subsequent ratoons, usually 3 or 4. On average, the sugarcane paddocks received 165 kg N/ha annually as urea during the last 50 years
The banana paddock had been under continuous banana production during the last 15-18 years following unfertilised pasture for [is greater than] 25 years. During the first 8 years of banana cropping, the paddock received NPK at 410, 80, and 440 kg/ha.year, respectively, as urea, superphosphate, and muriate of potash. The blended fertiliser was applied at intervals of 6-8 weeks. During the first 3-5 years the paddocks also received dolomite at 2 t/ha.year and one application of rock phosphate at 2 t/ha.year. During the most recent 8-9 years the banana crop received NPK at 350, 70, and 1100 kg/ha.year from the same sources and frequency, and lime at 1 t/ha. year.
The pasture paddock received blended NPK blend at 490, 40, 80 kg/ha.year during the last 21 years. The blended fertiliser was based on urea, diammonium phosphate, and muriate of potash, applied at least 3 times during the year. Dairy cows, at a stocking rate of 3-5 animals/ha, grazed the pasture continuously.
The soils in the study area belong to the Ferrosols Great Soil Group (Isbell 1994), locally known as the Pin Gin series (Gillman and Abel 1987), which are red to brown, acidic, well-structured clay soils formed on basalt, with deep profiles ranging from 1 m to [is greater than] 10 m. The cultivated Pin Gin series is characterised by high clay content, ranging from 62% to 68%, and tending to increase down the profile to 0.90 m depth (Gillman and Abel 1987; Gillman and Sinclair 1987). The silt and organic matter contents in the Pin Gin series decreased with increasing depth from 21% to 16% and 2.0% to 0.6%, respectively. The pH (1:5 [H.sub.2]O) throughout the soil profile was 4.8. The AEC increased from 0.30 to 1.0 [cmol.sub.c]/kg with an increasing trend down the profile to 0.9 m. Total cations (TC) and CEC decreased with depth from 0.90 to 0.40 [cmol.sub.c]/kg for TC and from 4.1 to 2.4 [cmol.sub.c]/kg for CEC.
Soil cores (0.05 m dia.) were taken from the sites described previously to depths of 10-40 m. The cores were taken at 1.5-m depth increments, using a hydraulic rig, and placed in split PVC tubes, and segmented at 0.5-m depth increments. Subsamples were taken from each segment immediately after coring and stored at [is less than] 4 [degrees] C for nitrate-N and ammonium-N determination in the laboratory. The 0.5-m segmented cores were transported to the laboratory and air-dried. During air-drying, plant material, gravel, and stones were hand removed and the air-dried material was ground to [is less than] 2 mm. These samples were used in the laboratory for the determination of soil CEC, AEC, pH, [Ca.sup.2+], [Mg.sup.2+], [K.sup.+], [Na.sup.+], and [Cl.sup.-] (Rayment and Higginson 1992). The TC is defined as the sum of [Ca.sup.2+], [Mg.sup.2+], [K.sup.+], and [Na.sup.+]. For consistency, the results are reported only for the top 10 m depth.
The data from the rainforest are considered to represent the undisturbed natural system and served as the background against which the cultivated sites were compared. To overcome any scepticism about the repeatability and validity of the results due to lack of replications at a given site, the data were subjected to different statistical tests. First, the distribution data for a given attribute under the rainforest were compared with the corresponding data from a given cultivated site using the paired t-test, with the data paired at 0.50-m depth increments. The pair-wise comparison was repeated on the data paired at 1.0-m depth increments. The latter was performed to determine whether any correlation existed between depth-incremented data within a profile. Both analyses produced similar results, providing evidence for no correlation between depth-incremented data of a given profile, and the differences or lack of difference between rainforest and a given site or that between sites is real. Second, a 1: 1 test between two given sites was performed for a given attribute, to determine whether the distribution of the attribute between the sites was significantly different. The analyses of the paired t-test and that from the 1:1 test for a given attribute belonging to 2 sites, for the 0.50-m depth-incremented data, produced similar results, indicating the results from this study, without replicated coring at a given site, are repeatable and valid. However, only the results from the paired t-test are reported in the text. Simple linear correlation was performed to determine the association between nitrate and the corresponding CEC, AEC, pH, [Cl.sup.-], or TC distribution separately for each site. The cumulative effect of the soil variables on nitrate-N retention was explored using a stepwise multi-variable selection procedure on the data pooled from the sugarcane and banana sites. The SAS (1991) software package was used for the above purpose.
Results and discussion
Nitrate-N distributions in the soil profiles, except under pasture, are shown in Fig. 2. As the concentrations of nitrate-N under pasture were below the detection limit ([is less than] 0.1 mg/kg), the main focus will be on sugarcane, banana, and rainforest sites. Nitrate-N concentrations in the soil profiles ranged from 0 to 33 mg/kg for sugarcane, 0 to 6.9 mg/kg for banana, and from 0 to 0.3 mg/kg for rainforest (Table 1). The striking feature is the high concentrations between 2 and 8 m under sugarcane and banana (Fig. 2). The paired t-test indicated that the average nitrate under sugarcane or banana was significantly (P = 0.05) higher than that under rainforest, indicating fertiliser/cropping-induced changes in nitrate accumulation in these soils (Table 2).
[Figure 2 ILLUSTRATION OMITTED]
[TABULAR DATA 1 NOT REPRODUCIBLE IN ASCII]
Table 2. Summaries of the paired t-test performed for nitrate-N, pH, chloride, cation exchange, anion exchange, and exchangeable cation distributions in soil profiles
Means are given on the diagonal while level of significance of the pairwise comparisons is given in the upper off-diagonals
Rain- Cane-130 Cane-118 Banana forest Nitrate-N Cane-130 2.58 (*) (*) (*) Cane-118 -- 12.49 (*) (*) Banana -- -- 1.08 (*) Rainforest -- -- -- 0.15 pH Cane-130 5.02 n.s. n.s. (*) Cane-118 -- 4.91 (*) (*) Banana -- -- 5.20 (*) Rainforest -- -- -- 5.31 Chloride Cane-130 30.90 (*) n.s. (*) Cane-118 -- 63.70 (*) (*) Banana -- -- 28.90 (*) Rainforest -- -- -- 15.00 Cation exchange Cane-130 2.02 n.s. n.s. (*) Cane-118 -- 2.17 n.s. (*) Banana -- -- 2.37 (*) Rainforest -- -- -- 1.31 Anion exchange Cane-130 1.77 n.s. (*) (*) Cane-118 -- 2.31 n.s. (*) Banana -- -- 2.38 (*) Rainforest -- -- -- 3.01 Total cations Cane-130 0.70 (*) n.s. (*) Cane-118 -- 0.28 n.s. n.s. Banana -- -- 0.51 n.s. Rainforest -- -- -- 0.27
(*) P < 0.05; n.s., = not significant.
Using the procedure of Wong et al. (1990), the values presented in Fig. 2 were used to compute the amount of nitrate in the top 10 m depth, i.e. the N-load, assuming a bulk density of 1.5 Mg/m. The computations revealed 345 kg N/ha under cane-130, 1875 kg N/ ha under cane-118, 145 kg N/ha under banana, and 21 kg N/ha under rainforest. Recent research on another 16 deep (10-12 m) cores taken from under sugarcane on 8 Ferrosols in JRC has shown that the N-load in profiles ranged from 44 to 4700 kg N/ha, and the average N-load was 1085 kg N/ha (Rasiah et al. 2000). It is thus evident that nitrate accumulation in Ferrosols under cropping, particularly under sugarcane, in the JRC is not uncommon.
Based on the average fertiliser N input data provided by growers (150 kg N/ha.year and banana 375 kg N/ha.year), the total amount of N applied during the last 50 years for sugarcane was calculated as 7500 kg/ha compared with 6000 kg/ha for banana during the last 16 years. Using the computed values of N retained in the top 10 m, provided in the previous paragraph, it is evident that about 25% of the fertiliser N applied during the last 50 years is retained under cane-118, compared with ~5% for cane-130, and ~3% for banana. Previous studies on the Ferrosols of this catchment showed that an average of ~ approx. 35% of the applied fertiliser N leached below the crop root-zone over a period of 3 years (Prove and Moody 1997). Thus, it can be inferred that ~70% of the N leached below cane-118 root-zone was retained in the top 10 m compared with 14% for cane-130 and 7% for banana. From the foregoing, we suggest that 30% of the nitrate that leached below cane-118 root-zone entered deep groundwater or lateral flow, and/or was denitrified compared with 86% for cane-130, and 93% for banana. The results from the latest 16 deep cores (mentioned in the previous paragraph) show that ~30% of the nitrate that leached below sugarcane root-zone was retained in the profiles (Rasiah et al. 2000).
Insignificant amounts of nitrate in the profile under grazed pasture suggest that leaching below the pasture root-zone was low. This contrasts with the results of other workers from Australia and New Zealand (Steele et al. 1984; Field et al. 1985; Steele and Vallis 1988; Bolan et al. 1991), who have reported that nitrate leaching is common under fertilised pasture. We will explore later in the text the reason for this inconsistency.
Other soil attributes
The AEC distribution (Fig. 3) under cropped soil profiles ranged from 0.19 to 3.41 [cmol.sub.c]/ kg compared with 2.01-4.12 [cmol.sub.c]/kg for rainforest (Table 1). The paired t-test indicated that AEC distributions varied within and among the profiles, and in general, were higher under rainforest than cropped soil (Table 2). The AEC distributions shown in Fig. 3 for cane-118 and rainforest suggest a trend existed for AEC to decrease with increasing depth, and similar trends existed in the other profiles (data not shown).
[Figure 3 ILLUSTRATION OMITTED]
The distributions of [Cl.sup.-], pH, and TC in the profile for cane-118 and rainforest are also shown in Fig. 3. Assuming the distribution under rainforest represents a stable natural system, then deviations from the rainforest are considered to be fertiliser/cropping-induced. It is evident from these figures that the distributions, for a given attribute, varied within and among profiles and were modified by fertiliser/cropping. The paired t-test showed significant differences between cropped and rainforest profiles for all the attributes in most of the comparisons (Table 2). Chloride content under cropping was higher than under rainforest, ranging from 1 to 164 mg/kg compared with 0 to 16 mg/kg for rainforest (Table 1). The source for relatively large quantities of [Cl.sup.-] under cropping was the applied muriate of potash. The TC under rainforest was less than cropping and it ranged from 0.14 to 0.49 [cmol.sub.c]/kg compared with 0.03 to 4.02 [cmol.sub.c]/kg for cropping. The source for higher TC under cropping is probably that derived from the applied fertilisers. The pH distributions under rainforest ranged from 5.2 to 5.7 compared with 4.6 to 6.9 for cropping (Table 1). The CEC under cropping ranged from 1.3 to 2.9 [cmol.sub.c]/kg compared with 0 to 2.1 [cmol.sub.c]/kg for rainforest.
Relationship between nitrate-N and soil attributes
Using simple correlation analysis, the associations between soil chemical attributes and nitrate were explored. The analysis indicated that most of these attributes were significantly associated with the nitrate retained in the profiles, particularly that under cane-130 (Table 3). Chloride was positively associated with nitrate under sugarcane and banana. The negative association between soil pH and nitrate was consistent for cane and rainforest. The AEC was positively associated with nitrate for cane-130 only. Significant negative association existed between TC and nitrate for cane-130 and rainforest. The association trends observed in our study are consistent with the leaching column results obtained by several other workers (Singh and Kanehiro 1969; Kinjo and Pratt 1971b; Espinoza et al. 1975; Wong et al. 1990; Kamewada 1994; Katou et al. 1996).
Table 3. The associations between nitrate-N and soil attributes pH, Cl, Ca, Na, K, anion exchange (AEC), cation exchange (CEC) capacities, total cations (TC), and dependence of nitrate-N on soil attributes as determined by multiple regression analysis
Only the significant correlations are reported
Equation r Cane-130 NO3 = 19.78 - 3.44 pH -0.66(**) NO3 = 0.76 + 0.065 C1 +0.64(**) NO3 = 2.69 - 0.26 CEC -0.46(*) NO3 = 1.17 - 0.53 AEC +0.33(*) NO3 = 2.39 - 0.25 TC -0.52(*) Cane-118 NO3 = 203.78 - 38.98 pH NO3 = 0.30 Cl - 5.72 +0.83(***) Banana NO3 = 0.047 C1 - 0.20 =0.81(***) Rainforest NO3 = 0.80 - 0.092 pH -0.42(*) NO3 = 0.13 - 0.0048 TC -0.32(*) Poole data NO3 = 152.01 - 29.11 pH -0.56(*) NO3 = 0.19 C1-0.91 +0.76(**) NO3 = 13.50 - 10.98 TC -0.43(*) Cl = 598.0 - 111.61 pH -0.54(*) C1 = 72.44 - 51.44 TC -0.51(*) [R.sup.2] [NO.sub.3] = 86.23 + 0.67(***) 1.53 AEC - 17.74 pH + 0.29 Cl - 0.071 AEC. Cl
(*) P < 0.05; (**) P < 0.01; (***) P < 0.001.
Because, AEC, [Cl.sup.-], TC, and pH were associated with nitrate retention under cropping, we anticipated that the interactions involving these variables might help us to understand better the influence of these attributes on nitrate retention. The association between AEC and pH or TC indicated that AEC under cropping was higher when the soil was more acidic or low in TC (not shown). The [Cl.sup.-] under cropping increased with increasing AEC. The association between [Cl.sup.-] and pH was negative, whereas that between pH and TC was positive. These interactions in different directions suggest that unlike leaching column experiments, the influence of soil attributes on N-retention under field conditions is interrelated and simple association results may be of limited use in explaining a complex situation.
The cumulative effect of the soil chemical attributes on nitrate retention, under cropping, was explored using the step-wise selection procedure on the data pooled among the cultivated sites. This analysis indicated that nitrate retention under cropping depended consistently on [Cl.sup.-], AEC, pH, and an interaction involving AEC and [Cl.sup.-] (Table 3). Nitrate retention increased with increasing AEC, [Cl.sup.-], and acidity, and decreased with the interaction term AEC.[Cl.sup.-]. The negative interaction involving AEC and [Cl.sup.-] suggests that [Cl.sup.-] adsorption at exchange decreased nitrate adsorption and retention. The analysis showed that pH, [Cl.sup.-], and AEC accounted for 67% of the variability in nitrate retention under cropping.
The amount of [Cl.sup.-] retained is 2-3 times higher than nitrate (Figs 2 and 3), suggesting competitive or preferential [Cl.sup.-] adsorption at anion exchange site or higher [Cl.sup.-] input, or lower [Cl.sup.-] crop-uptake, and/or slower transport of [Cl.sup.-] out of the profile. The results from leaching column experiments indicate competitive [Cl.sup.-] adsorption at equivalent ionic concentrations of [Cl.sup.-] and nitrate (Katou et al. 1996; Kinjo and Pratt 1971b), and provide evidence for competitive [Cl.sup.-] adsorption in the JRC profiles.
Katou et al. (1996) showed that nitrate was transported and adsorbed ahead of [Cl.sup.-] and the late-arriving [Cl.sup.-] subsequently replaced some of the adsorbed nitrate. This suggests that potential exists for the adsorbed to desorb, particularly during the wet season in JRC, and enter shallow groundwater that develops during the wet season and/or to enter deep groundwater.
At maximum [Cl.sup.-] adsorption, 164 mg/kg or 0.46 [cmol.sub.c]/kg, the nitrate adsorption was 30.4 mg/kg or 0.049 [cmol.sub.c]/kg and the AEC was 1.63 [cmol.sub.c]/kg. This implies that only 31% of the anion exchange sites were occupied by both nitrate and [Cl.sup.-]. Similarly at maximum nitrate adsorption, 40.1 mg/kg or 0.065 [cmol.sub.c]/kg, the [Cl.sup.-]adsorption was 133 mg/kg or 0.38 [cmol.sub.c]/kg and the AEC was 2.41 [cmol.sub.c]/kg, suggesting that only ~18% of the anion exchange sites being occupied by both nitrate and [Cl.sup.-]. It is evident that sufficient charged sites were available for the adsorption by other anions, such as sulfate.
Nitrate retention capacity
We have shown the AEC of the Ferrosols in JRC is high (Table 2) and provides conditions favourable for adsorption and retention of nitrate. Wong et al. (1990) showed that one-half of 1 [cmol.sub.c]/kg of AEC in the plough zone (2000 t soil/ha) had the capacity to hold 140 kg of nitrate-N/ha, whereas the other half was occupied by other anions. Using their computational procedure, we found the Ferrosols possess the capacity to hold 17.6 t nitrate-N/ha under cane- 130, 22.4 t nitrate-N/ha under cane-118, 25.0 t nitrate-N/ha under banana, and 31.6 t nitrate-N/ha under rainforest in the top 10 m depth. When the nitrate-N holding capacity was computed for the plough layer (0-0.2 m), the values ranged from 350 to 630 kg nitrate-N/ha. Because the AEC of our Ferrosols is 2-6 times higher than that of Wong et al. (1990), the retention capacity of the Ferrosols can be considered to be high. Even though the nitrate adsorption and retention capacity of the Ferrosols is high, it is not known whether the adsorbed nitrate would re-enter aqueous phase when the nitrate load in the profile approaches the potential maximum capacity.
Large quantities of nitrate found in Ferrosol profiles under sugarcane and banana provide evidence for fertiliser-derived nitrate accumulation and retention under cropping in the JRC. The retention, observed mostly between 2 and 8 m (well below the crop root-zone), indicates that the nitrate leaching below the crop root-zone was accumulating at depth in the profile. The nitrate retained in the profile, estimated to range from 7% to 70% of that leached below the crop root-zone, provides evidence that nitrate adsorption in Ferrosols is a major mechanism that determines the fate of the nitrate leaching below crop root-zone. Estimates showing that Ferrosols possess a large capacity (17-32 t/ha. 10 m) to hold nitrate suggest that nitrate loading into water bodies will be substantially reduced by this buffering mechanism. The nitrate retention ability and capacity of Ferrosols provide a narrow window of opportunity to develop best N fertiliser management strategies before the profiles approach their potential maximum retention capacity. Once the profiles are saturated with nitrate to their maximum retention capacity, thereafter, the nitrate leaching below the crop root-zone may enter water bodies directly, thereby increasing the risk of N-loading in water bodies. Development of new and/or modifications to current N fertiliser management practices are essential.
The authors gratefully acknowledge the financial support provided by the Sugar Research and Development Corporation of Queensland, and the field and laboratory support provided by Dr B. Prove, Messrs. D. Heiner, E. K. Best, Rob Lait, M. D. Johnson, and T. J. McShane, and Ms Rebecca-Lee Ritchie. The constructive comments by provided Dr D. Curtin and Mr D. Reid on the first draft of the manuscript were very useful in improving the quality of the manuscript.
Black AS, Waring SA (1976a) Nitrate leaching and adsorption in a Krasnozem from Redland Bay, Qld. I. Leaching of banded ammonium nitrate in a horticultural rotation. Australian Journal of Soil Research 14, 171-180.
Black AS, Waring SA (1976b) Nitrate leaching and adsorption in a Krasnozem from Redland Bay, Qld. II. Soil factors influencing adsorption. Australian Journal of Soil Research 14, 181-188.
Black AS, Waring SA (1976c) Nitrate leaching and adsorption in a Krasnozem from Redland Bay, Qld. III. Effect of nitrate concentration on adsorption and movement in soil columns. Australian Journal of Soil Research 14, 189-195.
Black AS, Waring SA (1979) Absorption of nitrate, chloride and sulphate by some highly weathered soils from south-east Queensland. Australian Journal of Soil Research 17, 271-282.
Bolan NS, Hedley MJ, White RE (1991) Processes of soil acidification during nitrogen cycling with emphasis on legume based pastures. Plant and Soil 134, 53-63.
Bonell M, Gilmour DA, Cassells DS (1983) A preliminary survey of the hydraulic properties of the rainforest soils in the tropical North-east Queensland and their implications for the runoff process. Catena Supplement 4, 57-78.
Cotching B (1995) Long-term management of Krasnozems in Australia. Australian Journal of Soil and Water Conservation 8, 18-27.
Daniells JW (1995) Results of a survey of research/development priorities and crop management practices in the north Queensland banana industry. Department of Primary Industries, Queensland, QB 95001.
Deshpande TL, Greenland DJ, Quirk JP (1964) Influence of iron and aluminium oxides on the charges of clay minerals. Transactions of the 8th International Congress. Soil Science 3, 1213-1225.
Espinoza W, Gast RG, Adams RS Jr (1975) Charge characteristics and nitrate retention by two Andepts from South-Central Chile. Soil Science Society of America Proceedings 39, 824-846.
Field TRO, Theobald PW, Ball PR, Clothier BE (1985) Leaching loss of nitrate from cattle urine applied to a lysimeter. Proceedings Agronomy Society 15, 137-141.
Fordham GP (1973) Location of iron-55, strontium-85, and iodide-125 sorbed by kaolinite and dickite particles. Clays and Clay Minerals 20, 175-184.
Gillman GP, Abel DJ (1987) A summary of surface charge characteristics of the major soils of the Tully-Innisfail Area, North Queensland. CSIRO Division of Soils, Divisional Report No. 85.
Gillman GP, Sinclair DF (1987) The grouping of soils with similar charge properties as a base for agrotechnology transfer. Australian Journal of Soil Research 25, 275-285.
Hair ID (1990) Hydrogeology of Russell and Johnstone Rivers alluvial valleys, North Queensland. ISBN 1034 7399, Department of Resource Industries, Queensland Government, Australia.
Hingston FJ, Posner AM, Quirk JP (1972) Anion adsorption by goethite and gibbsite. 1. The role of protons in determining adsorption envelopes. Journal of Soil Science 23, 177-192.
Isbell RF (1994) Krasnozems--a profile. Australian Journal of Soil Research 32, 915-929.
Ishiguro MK, Song C, Yuita K (1992) Ion transport in an allophanic Andisol under the influence of variable charge. Soil Science Society of America Journal 56, 1789-1793.
Kamewada K (1994) Vertical distribution of anions ([Cl.sup.-], [ILLUSTRATION OMITTED][MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) in upland soils. (In Japanese). Japanese Journal of Soil Science and Plant Nutrition 65, 255-265.
Katou H, Clothier BE, Green SR (1996) Anion transects involving competitive absorption during transient water flow in an Andisol. Soil Science Society of America Journal 60, 1368-1375.
Kinjo T, Pratt PF (1971a) Nitrate adsorption. I. In some acid soils of Mexico and South America. Soil Science Society of America Proceedings 35, 722-725.
Kinjo T, Pratt PF (1971b) Nitrate adsorption II. In competition with chloride, sulfate, and phosphate. Soil Science Society of America Proceedings 35, 725-728.
Moody PW, Reghenzani JR, Armour JD, Prove BG, McShane TJ (1996) Nutrient balances and transport at farm scale--Johnstone River Catchment. In `Proceedings of the Conference on Downstream Effects of Land Use'. Rockhampton, 1995. (Eds AG Eyles, HM Hunter, GE Rayment) (Department of Natural Resources: Qld)
Okumara Y, Wada K (1983) Electric charge characteristics of Ando (B) and Red-Yellow B soils and weathered pumices. Journal of Soil Science 34, 287-295.
Prove BG, Moody PW (1997) Final report on nutrient balance and transport from agricultural and rainforest lands. Department of Natural Resources, South Johnstone, Qld.
Quirk JP (1960) Negative and positive adsorption by kaolinite. Nature 188, 253-254.
Rasiah V, Menzies N, Armour JD (1999) Progress report for Milestone 3 (April/2000) on: Nitrate retention at depth. Unpublished Report, Department of Natural Resources, South Johnstone, Qld.
Rasiah V, Menzies N, Armour JD (2000) Progress report for Milestone 4 (April/2000) on: Nitrate retention at depth. Unpublished Report, Department of Natural Resources, South Johnstone, Qld.
Rayment GR, Higginson FR (1992) `Australian laboratory handbook of soil and water chemical methods.' (Inkata Press: Sydney)
SAS (1991) SAS/STAT procedure guide for personal computers. Version 5. Statistical Analysis Systems Institute Inc. Cary, NC.
Schofield RK (1949) Effect of pH on electric charges carried by clay particles. Journal of Soil Science 1, 1-18.
Schofield RK, Samson HR (1953) The deflocculation of kaolinite suspensions and accompanying change over from positive to negative charge. Clay Mineral Bulletin 2, 45-51.
Singh BR, Kanehiro Y (1969) Adsorption of nitrate in amorphous and kaolinitic Hawaian soils. Soil Science Society of America Proceedings 33, 681-683.
Steele KW, Judd M J, Shannon PW (1984) Leaching of nitrate and other nutrients from a grazed pasture. New Zealand Journal of Agriculture Research 27, 5-11.
Steele KW, Vallis I (1988) The nitrogen cycles in pastures. In `Advances in nitrogen cycling in agricultural ecosystems'. (Ed. JR Wilson) pp. 274-291. (CAB International: Wallingford, UK)
Sumner ME (1963) Effect of iron oxides on positive and negative charges in clay and soil. Clay Mineral Bulletin 5, 218-226.
Sumner ME, Reeve NG (1966) The effect of iron oxide impurities on the positive and negative adsorption of chloride by kaolinite. Journal of Soil Science 17, 274-279.
Tweneboah CK, Greenland DJ, Oades JM (1967) Changes in charge characteristics in soils after treatment with 0.5 M calcium chloride at pH 1.5. Australian Journal of Soil Research 5, 247-261.
Wada K, Harward ME (1974) Amorphous clay constituents of soils. Advances in Agronomy 26, 211-216.
Wong MT, Hughes FR, Rowell DL (1990) Retarded leaching of nitrate in acid soils from the tropics: Measurement of the effective anion exchange capacity. Journal of Soil Science 41,655-663.
Yellowlees D (1991) Land use patterns and loading of the Great Barrier Reef region. In `Proceedings of the Workshop held at James Cook University'. 1990. Sir George Fisher Centre for Tropical Marine Studies (Ed. D. Yellowlees) pp. 53-66. (James Cook University: Townsville, Qld)
Manuscript received 19 November 1999, accepted 25 August 2000
V. Rasiah(A)(C) and J. D. Armour(B)
(A) Department of Natural Resources, Centre for Wet Tropics Agriculture, PO Box 20, South Johnstone, Qld 4859, Australia.
(B) Department of Natural Resources, Centre for Tropical Agriculture, PO Box 1054, Mareeba, Qld 4880, Australia.
(C) Corresponding author; email: email@example.com
|Printer friendly Cite/link Email Feedback|
|Author:||Rasiah, V.; Armour, J. D.|
|Publication:||Australian Journal of Soil Research|
|Article Type:||Statistical Data Included|
|Date:||Mar 1, 2001|
|Previous Article:||Rotation crops for irrigated cotton in a medium-fine, self-mulching, grey Vertosol.|
|Next Article:||Changes in chemical nature of soil organic carbon in Vertisols under wheat in south-eastern Queensland.|