Decomposition of sugarcane harvest residue in different climatic zones.
Management of soil organic matter is critically important for sustaining the long-term productivity of cropped soils. Key components of such management include an effective system of crop residue management, appropriate cultivation practices, and a fertilisation regime that replaces nutrients lost through crop harvesting (Foltett et al. 1987). The concept of environmental sustainability demands that this be achieved without diminishing the quality of soil, air, and water resources in the wider environment.
The Australian sugar (Sacharum spp.) industry is concentrated along the eastern coast of Queensland and northern New South Wales, a region that coincides with many environmentally sensitive natural areas, including the Great Barrier Reef. Nutrient levels in some river and marine systems are believed to have increased substantially since European settlement due to inputs from agricultural, commercial, and residential activities (Furnas 2002; Productivity Commission 2003). The sugarcane industry may be a contributor to the nutrient loads in these systems, being located primarily on the coastal plains and river valleys, and being a large user of nitrogen (N) fertilisers (Productivity Commission 2003).
Recommended N fertiliser applications for sugarcane are generally 100-200 kg N/ha.year (Calcino 1994), and are based on the traditional system of management where harvest residues (trash) are burnt and the soil cultivated every year. Over the last 25 years, however, sugarcane growers have increasingly adopted a system of green cane trash blanketing (GCTB), where trash is retained as an undisturbed layer on the soil surface and cultivation is greatly reduced. Around 70% of the Australian sugar crop is currently grown under GCTB (Kingston and Norris 2001). The GCTB system is seen as being more environmentally benign than the burnt system because it dramatically reduces runoff and soil erosion (Prove et al. 1995), and avoids air quality issues arising from smoke and particulate matter.
Sugarcane trash contains around 60% of the total above-ground plant N (Chapman et al. 1994) and when it is burnt, >70% of the carbon (C) and N are lost to the atmosphere (Mitchell et al. 2000). Consequently, with retention of trash, N and C may be accumulating in the soil. However, little is known about the effects of sugarcane trash retention on the dynamics of soil C and N, despite the importance of these processes for soil fertility, crop nutrient availability, fertiliser requirements, and risks of N losses off-site.
In any cropping system involving residue retention, the factors dominating soil C and N dynamics are likely to be the mass of residue returned at harvest and the rate of residue decomposition, which is related to the C and N contents of the residue. Thus, in order to understand the effects of trash retention on N dynamics, trash composition and decomposition need to be understood.
The objective of this work was to measure returns and decomposition of sugarcane trash under the GCTB system, in terms of dry matter (DM), C, and N, in contrasting climatic conditions. The effects of trash retention on soil C and N are reported separately (Robertson and Thorburn 2007).
Trash decomposition was measured between October 1996 and August 1998 in 5 field experiments in 3 contrasting climatic zones: Harwood (northern New South Wales, subtropical); Mackay (central Queensland, tropical); and Tully (northern Queensland, wet tropical). None of the sites had previously been under GCTB management. Site information is shown in Fig. 1 and Table 1.
[FIGURE 1 OMITTED]
In each experiment a sugarcane crop (variety Q 124) managed under the GCTB system was mechanically harvested and the trash left undisturbed on the soil surface. In both Harwood and Mackay there were 2 experiments, one where the crop was harvested early in the season, and one where the crop was harvested late in the season. The Tully experiment was harvested late in the season. The experiments were divided into 4 replicate plots at Harwood (15 m by 6 rows) and Mackay (18 m by 4 rows) and 3 replicate plots at Tully (10 m by 6 rows). In each case, the row spacing was 1.5 m.
For each experiment, the mass of trash deposited after harvest was estimated by weighing the trash in 10 randomly placed quadrats (I.50 by 0.75 m) per replicate plot. The average from these quadrats was used as the standard mass of trash for that replicate plot. At Harwood and Mackay, the content of the quadrats was divided into cut trash (individual leaves or parts of leaves) and whole tops (uppermost 200-300 mm of the plant with leaves attached).
To measure trash decomposition, quadrats (1.50 by 0.75 m) were laid across the rows of sugarcane, and underlying trash removed. Sufficient quadrats were prepared to allow 7-9 destructive samplings per replicate (see Table 1). The measured standard mass of trash was then placed in the quadrat. At Harwood and Mackay, cut trash and tops were returned in the same proportions as deposited after harvest. The quadrats were held in place by steel pegs, and covered with netting (20-mm mesh) to secure the trash and prevent dead leaves that detached from the crop during the season from being added to the quadrat.
At intervals of approximately 4-6 weeks over the following year, one quadrat was destructively sampled per replicate. Sampling dates are shown in Table 1. First, all trash that detached easily from the soil (termed 'free trash') was removed by hand from the quadrat and retained. Trash that had become incorporated with the soil (termed 'incorporated trash') was then sampled by removing soil and trash from a strip (0.175 m wide by 1.50m long by ~0.02 m deep) down the middle of the quadrat.
The crops were fertilised within 6 weeks of harvest, according to the usual grower practice in the region (160-200 kg N (as urea), 14-20kg P, 90-125kg K, and 16-25kg S). Fertiliser was applied on the surface of the trash in Harwood and Tully, and ~0.10 m below the trash using a stool-splitter in Mackay. The Mackay experiments each received 70 mm of irrigation; the Harwood and Tully experiments were not irrigated.
Climatic conditions at experimental sites
Climate data were recorded on site. Data for the Harwood experiments contained gaps due to failure of the equipment, which were filled using data from the nearest Bureau of Meteorology site (Bushgrove for rainfall, Grafton for temperature), modified according to an equation obtained by linear regression of site data and Bureau of Meteorology data for summer and winter.
Monthly rainfall and temperature during the experimental period are shown in Fig. 2. Temperatures generally decreased in the order Tully > Mackay > Harwood, with the greatest difference being in winter minimum temperature (max. temp. was 32[degrees]C at all sites; min. temp. was 13.8, 10.4, and 4.3[degrees]C at Tully, Mackay, and Harwood, respectively). Long-term mean annual rainfall was 4060mm at Tully, 1670mm at Mackay, and 1020mm at Harwood. Monthly rainfall was generally within 25% of the long-term average, except in February 1997 at Mackay, when it was twice the average. The number of rainy days decreased in the order Tully > Harwood > Mackay (Table 2).
[FIGURE 2 OMITTED]
Accumulated thermal time ([summation] Temperature) was calculated by summing mean daily air temperature since the harvest date, without subtraction of a base temperature (because temperatures did not fall below 0[degrees]C, the most appropriate base temperature for organic matter decomposition; Douglas and Rickman 1992).
Incorporated trash was separated from the soil by soaking and gently agitating the sample in 7 L of water for 2min, then removing floating organic matter by hand and suspended organic matter on a 2-mm sieve. This process was performed 4 times per sample. Any obvious non-trash material (e.g. coarse roots) was removed. This procedure may have overestimated the mass of incorporated trash, as background estimations of incorporated trash were not made in the burnt soils. Free trash was not washed, which may have resulted in overestimation of mass if the trash was contaminated with soil. Trash water content and DM were determined by drying at 70[degrees]C for 24-48 h. Trash was roughly ground (20-60 mm long by 3-6 mm wide) in a cutter-grinder and subsamples were ground to <500 [micro]m before determination of total N and C by dry combustion using a Leco induction furnace (Rayment and Higginson 1992).
The effects of sampling time were tested separately for each experiment by analysis of variance for a randomised complete block design using the SYSTAT[R] program (SPSS Inc.). Relationships between selected variables were investigated using Pearson correlation and linear regression. Unless otherwise stated, effects were taken as significant where Bonferroni probabilities were [less than or equal to] 0.05.
After harvest, 7-12 t of trash DM was returned per ha (means for individual experiments). Approximately 10 t of trash DM was returned for every 100 t fresh cane yield ([r.sup.2] = 0.64, P < 0.05). Trash DM estimates after harvest were very variable within plots (CV 23-45%). Trash water content was 19-30% (fresh weight basis) after harvest and 5-86% at the time of sampling.
The trash returned after harvest contained 3000-5000 kg C/ha and 28-54 kg N/ha. The return of C in trash was linearly related to cane yield ([r.sup.2] = 0.66, P < 0.05), but the return of N in trash was not. The initial concentration of C was very consistent (44.1-45.0%), but that of N was more variable (0.38-0.67%) among experiments (Fig. 3a-d). The initial trash C : N ratio was 70-117 (Fig. 3e, f).
[FIGURE 3 OMITTED]
During the 12 months after harvest, 82-98% of the free trash (surface trash, not incorporated with the soil) DM was decomposed (Fig. 4a, b). Over this time, 84-98% of the original C and 67 95% of the original N was lost from free trash (Fig. 4c-f). In other words, 50-800 kg C/ha and 1-20 kg N/ha remained in free trash at the end of the year. The rate of C loss from free trash was almost identical to the rate of DM loss ([r.sup.2] = 0.99, n = 43, P < 0.001). The concentration of C in free trash declined with time, whereas that of N increased, the C : N ratio falling to around 40 in late-harvested crops and 30 in early-harvested crops (Fig. 3).
[FIGURE 4 OMITTED]
The rate of DM decomposition was significantly correlated with average daily air temperature and average daily rainfall at both Harwood and Mackay (Fig. 5a, b). Decomposition rate was also positively correlated with the proportion of rainy days at Mackay (Fig. 5c). At Tully, DM decomposition was apparently not related to any of these parameters (Fig. 5). Periodic moisture deficit (calculated as rainfall minus evaporation) was less closely related to decomposition rate than was rainfall alone (data not shown). Rainfall and the proportion of rainy days were correlated at Tully ([r.sup.2] = 0.68) and Mackay ([r.sup.2] = 0.42) but not at Harwood. Temperature and rainfall were correlated at all sites ([r.sup.2] = 0.40, 0.38, and 0.36 for Harwood, Mackay, and Tully, respectively).
[FIGURE 5 OMITTED]
Cumulative trash DM decomposition across all experiments could not be described by a single relationship with cumulative time (Fig. 6a). Cumulative DM decomposition showed a linear relationship with cumulative thermal time ([summation] Temperature, Fig. 6b), although considerable departure from the line remained for some sampling points. Cumulative decomposition could not be described by a single relationship with cumulative rainfall (data not shown).
[FIGURE 6 OMITTED]
Cumulative net loss of N from free trash could not be adequately described by a linear relationship with cumulative time or [summation] Temperature (data not shown). The relationship between cumulative N loss and cumulative C loss was different across experiments (see Fig. 7, where all experiments except Tully fitted a linear model; Mackay (early) fitted a quadratic model; and Mackay (late) and Tully fitted a broken stick model). Most sites showed 2 phases of decomposition: an early phase (up to around 40% C loss) when N loss was less than and not related to C loss; and a late phase (>40% C loss) when N loss was related to C loss, although the slope of the relationship varied significantly between sites (Fig. 7). There appeared to be similar relationships between the rate of N loss from free trash and the C : N ratio of that trash (Fig. 8), although the C : N ratio at which significant N loss began ranged between 60 and 78 for the different sites.
[FIGURES 7-8 OMITTED]
Incorporated trash (trash incorporated into the top 0.02 m of soil) contained 1000-2600 kg DM/ha, 370-860 kg C/ha, and 18-27 kg N/ha, with no apparent time trends or differences among experiments (data not shown). The C concentration was variable (26-41%) with no trends in time, and the N concentration (0.9-1.4%) tended to rise during the year (Fig. 3a-d). The C : N ratio of incorporated trash remained within a fairly narrow range, declining from around 30-40 at the start of the year to around 20-30 at the end (Fig. 3e, f). By the end of the year, the incorporated trash contained at least as much C and N as remained in the free trash (400-800 kg C/ha and 20-27 kg N/ha).
Trash DM, C, and N returned after harvest
The quantity of trash DM returned in sugarcane systems under GCTB (7-12 t/ha in our experiments; 6-20 t/ha in other studies; Wood 1991; Spain and Hodgen 1994; Mitchell and Larsen 2000) is large in comparison with the mass of harvest residues from most agricultural crops (e.g. 2-6 t DM/ha from wheat, barley, and sorghum; Myers 1983; Buyanovsky and Wagner 1986; Curtin and Fraser 2003), but is similar to the mass of residues from corn (e.g. 9-14 t/ha; Buyanovsky and Wagner 1986). The relationship between average trash return and cane yield in this study (10 t DM/100 t) was similar to that measured for other cane varieties by Mitchell and Larsen (2000).
The trash from newly harvested sugarcane contained significant quantities of N (48-55kg/ha in Harwood and Mackay, 27 kg/ha in Tully). The small N return in Tully reflected the small yield (79t/ha in the year of this study compared with an average of 111 t/ha in previous years, Alan Hurney, pers. comm.). The return of N in trash, however, could not be predicted adequately from the cane yield. Trash N concentration is variable because trash consists of varying proportions of live and dead leaves. These leaves, especially the live leaves, also have variable N concentrations. The return of C in trash could be estimated as 4400 kg C/ha per 100 t/ha fresh cane yield, because trash C concentration was almost identical in the different experiments.
The C : N ratio of fresh trash was high (70-117), although Spain and Hodgen (1994) measured a C : N ratio of 170 in sugarcane trash. Initial trash decomposition rates were therefore expected to be slow due to limited N availability. The residues of other crops with similarly high C : N ratios (e.g. wheat (73), Amato et al. 1987; barley (94), Christensen 1985) result in net immobilisation of N during decomposition, so N immobilisation was expected to predominate during the early stages of decomposition of sugarcane trash.
It took a year for essentially all (82-98%) of the trash blanket to decompose. This is in agreement with the 81% decomposition of a 15t DM/ha trash blanket in northern Queensland in a little less than a year recorded by Spain and Hodgen (1994). In a study using the APSIM simulation model, Thorburn et al. (2001) suggested that sugarcane trash decomposition was significantly slower than decomposition of residues such as those of cereals given the same environmental conditions and residue C : N ratio.
That rainfall and temperature were correlated with the rate of free trash DM decomposition in Harwood and Mackay concurs with the established notion that water availability and temperature are important controlling factors for organic matter decomposition (Stott et al. 1986). The correlation between the proportion of rainy days and decomposition at Mackay agrees with similar effects observed by Vanlauwe et al. (1995) during decomposition of various plant litters in dry tropical conditions. However, most of the variation in trash DM decomposition rate could not be attributed to rainfall or temperature, particularly in Tully. This may be partly because rainfall and temperature were not independent of the decomposition stage of the trash. It is also possible that air temperature and rainfall did not adequately reflect temperature and water availability at the trash-soil interface, where much of the decomposition would have occurred. Other factors such as soil, trash, and management were almost certainly also important for decomposition in these systems. For example, decomposition may have been affected by the degree of trash-soil contact (Magid et al. 2006), which would have increased as decomposition progressed. Trash characteristics not measured here, such as lignin or polyphenol content, may also have been important (Vanlauwe et al. 1997). Climate and soil interact in the proportion of soil pore space habitable by microorganisms, a factor shown to be an important control of microbial activity and decomposition (Young and Ritz 2000). That conditions were more favourable for microorganisms at Tully than at Mackay and Harwood is suggested by the larger soil microbial biomass at Tully (Robertson and Thorburn 2007), and may explain the more complete decomposition of trash at Tully. The strength of interactions among factors is likely to have varied among sites and throughout the year, making it difficult to isolate specific climatic effects (Parr and Papendick 1978).
Notwithstanding the fact that it was influenced by factors other than climate, cumulative trash decomposition across all sites could be approximated from a linear relationship with [summation] Temperature (Fig. 6b). This may appear contradictory to the lack of correlation between temperature and decomposition between sampling occasions at Tully (Fig. 5). However, as decomposition at Tully was not limited by temperature, the relationship between decomposition and E Temperature was no better than the relationship with time. At Mackay and Harwood, where decomposition was partially limited by temperature, using [summation] Temperature instead of time significantly improved the relationship. The climatic range represented by Tully, Mackay, and Harwood encompasses a large part of the Australian sugar industry, so it is likely that a similar relationship would hold at other sites. The relationship may be different where trash is incorporated into the soil, or under fully irrigated conditions. Linear relationships with DM decomposition and thermal time have also been reported for residues of similarly high C : N ratio, decomposing on the soil surface at several sites in North America (Douglas and Rickman 1992), although thermal time was much shorter and decomposition rates much slower than in the present study. Decomposition of residues incorporated into the soil was shown to have a curvilinear relationship with thermal time in North America (Douglas and Rickman 1992) and New Zealand (Curtin and Fraser 2003).
C and N loss during decomposition
Two phases of trash decomposition could be identified, corresponding with the relative availability of C and N. In the early phase, which lasted until 40-50% of DM or C had been lost, the C : N ratios were relatively high and variable among experiments. During this phase, net N loss or gain was not related to the amount of decomposition (C loss, Fig. 7). In the late phase, which began after 40-50% of DM or C had been lost, the C : N ratios were much reduced (<50) and similar in all experiments (Fig. 3e, f). During this phase, net N loss occurred in all experiments at a rate consistent with (and often faster than) C loss (Fig. 7).
Given the high initial C : N ratios of free trash, it is not surprising that net N release was delayed in most of the experiments during the first part of the year. In this respect, sugarcane trash behaved similarly to other crop residues with high C : N ratios, such as cereal straw (Christensen 1985; Jensen 1997). The initial gain in trash N at Tully (Fig. 4e) may have been due to the presence of fertiliser N or microbially immobilised N from soil or fertiliser. However, net N loss occurred at C : N ratios as high as 78 (Fig. 8). Rather than net N mineralisation, which is unlikely above a C : N ratio of ~35 (Alexander 1977; Christensen 1985), this N loss at high C : N ratio may have been due to loss of soluble trash N or fertiliser N associated with the trash (at all sites, fertiliser was applied while free trash C : N ratio was high; Robertson and Thorburn 2007).
During the late phase of decomposition, N loss from free trash probably occurred through a combination of 2 processes. First, movement of N from free trash to soil as a result of the growth of hyphae of(soil- or residue-based) fungi through the trash layer, a process which has been demonstrated to be important during decomposition of wheat straw (Frey et al. 2000). The declining C : N ratio of free trash with time indicated decomposition of free trash even though most of it was not in direct contact with the soil. The second process is transfer of N from the free to the incorporated trash pool through the consolidating effect of rainfall, the mixing effect of earthworms and other soil fauna, or partial decomposition by microorganisms. For most of the year, incorporated trash was in a more advanced stage of decomposition than free trash, as seen by its lower C : N ratio and smaller fragment size. At the end of the year, the C : N ratios of free and incorporated trash were similar (20-40) and low enough that some net mineralisation of N could be expected from their decomposition (Parr and Papendick 1978). The size of the incorporated trash pool remained fairly stable during the year, suggesting that the rates of addition and decomposition of incorporated trash were similar. However, the C content of incorporated trash at some samplings may have been underestimated because of contamination of the samples with soil, e.g. where C concentrations were <30% (Fig. 3b).
Spain and Hodgen (1994) studied C and N in decomposing sugarcane trash over 1 year at a site in tropical Queensland. Their results differ from ours in that they measured a net loss of 63% of trash N in the first 90 days while trash C : N ratios were between 171 and 241, and no net N loss thereafter. The authors explained this N loss as leaching of soluble trash N. However, the soluble N component of fresh sugarcane trash (including trash from this study) is around 20% of total N content (F. Robertson and P. Thorburn, unpublished data). The differing results obtained by Spain and Hodgen may have been influenced by the fact that, in their study, (1) the starting mass of trash was not controlled, (2) trash was observed to move from the row to the inter-row during the year and was sampled using small (<0.25 [m.sup.2]) quadrats, and (3) the initial trash N content was very low (0.26%).
The rate of N loss from free trash in the later part of the year (after Day 120) averaged 48-170 g/ha.day, or 1-5 kg N/ha.month in the different experiments (from linear regressions of N loss against time, [r.sup.2] was 0.65-0.92). This compares with mineral N already in the soil of 3-14 kg N/ha in the top 0.05m and 5-32 kg N/ha in the top 0.25 m, after the effect of fertiliser had diminished (Robertson and Thorburn 2007). This suggests that, even if all N lost from trash was plant-available, it would have been of limited significance for plant growth during the 12 months after harvest. This agrees with the finding of Ng Kee Kwong et al. (1987) and Chapman et al. (1992), who concluded that less than 10% of the N in isotopically labelled trash is taken up by the plant. However, this is not to suggest that trash retention is insignificant for crop nutrient availability and soil fertility; rather, the potential value of trash for soil C and N supply lies in its cumulative effects over the medium-long term (Robertson and Thorburn 2007).
Thank you to Graham Kingston, Alan Hurney, and Les Chapman for allowing this study to be superimposed on their field experiments and providing supporting data. Thank you to Kaylene Harris, Ruth Mitchell, Kylee Sankowsky, Patricia Nelson, and Jody Biggs for assistance with the field and laboratory work. Also thank you to Murray Hannah for advice on statistical analyses. We acknowledge funding from the Australian Government and Sugarcane Industry through the CRC for Sustainable Sugar Production, BSES Ltd, and the Sugar Research and Development Corporation.
Manuscript received 3 July 2006, accepted 11 December 2006
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Fiona A. Robertson (A) and Peter J. Thorburn (B)
(A) Corresponding author. BSES Ltd, and CRC for Sustainable Sugar Production, 50 Meiers Road, Indooroopilly, Qld 4068, Australia. Present address: Department of Primary Industries, PIRVic., Private Bag 105, Hamilton, Vic. 3300, Australia. Email: firstname.lastname@example.org
(B) CSIRO Sustainable Ecosystems and CRC for Sustainable Sugar Production, Queensland Bioscience Precinct, 306 Carmody Road, St Lucia, Qld 4067, Australia.
Table 1. Selected characteristics of the sites and experiments used to measure trash decomposition Experiment Harwood (Late) Harwood (Early) Location Northern New South Wales Climatic zone Subtropical Grid reference 29.50S, 153.20E Soil texture ^ Clay loam (26, 34, 40), reps 1 & 2; (%sand, %silt, %clay) clay (18, 28, 54) 40), reps 1 & 2; Cropping history Sugarcane (burnt), vegetables Soil pH (A) 4.78 4.95 Soil organic C (%) (A) 2.31 2.50 Soil total N (%) (A) 0.18 0.20 planting date July 1994 July 1994 Harvest date 1 Dec. 1996 14 Aug. 1997 Years of trash return 1 2 Replicates 4 4 Sampling dates (days 11 Dec. 1996 (10) 23 Aug. 1997 (9) after harvest) 11 Feb. 1997 (72) 26 Sept. (43) 31 Mar. (120) 26 Nov. (104) 15 May (165) 12 Jan. 1998 (151) 23 June (204) 13 Mar. (211) 6 Aug. (248) 30 Apr. (259) 25 Sept. (298) 29 June (319) 27 Nov. (361) 3 Aug. (354) Experiment Mackay (Late) Mackay (Early) Location Central Queensland Climatic zone Tropical Grid reference 21.10S, 149.07E Soil texture ^ Sandy loam (54, 26, 20) (%sand, %silt, %clay) Cropping history Sugarcane (burnt) Soil pH (A) 5.21 5.21 Soil organic C (%) (A) 1.77 1.43 Soil total N (%) (A) 0.11 0.08 planting date July 1992 July 1992 Harvest date 13 Nov. 1996 4 July 1997 Years of trash return 4 5 Replicates 4 4 Sampling dates (days 25 Nov. 1996 (12) 16 July 1997 (12) after harvest) 15 Jan. 1997 (63) 18 Aug. (45) 17 Mar. (124) 17 Sept. (75) 1 May (I 69) 12 Nov. (131) 4 June (203) 27 Jan. 1998 (207) 14 July (243) 30 Mar. (269) 16 Aug. (276) 18 May (318) 19 Sept. (3 10) 6 July (367) 21 Oct. (342) 4 Nov. (356) Experiment Tully Location Northern Queensland Climatic zone Wet tropical Grid reference 17.56S, 145.56E Soil texture ^ Clay (27, 34, 39) (%sand, %silt, %clay) Cropping history Sugarcane (burnt) Soil pH (A) 5.19 Soil organic C (%) (A) 1.60 Soil total N (%) (A) 0.13 planting date July 1990 7Harvest date 30 Oct. 1996 Years of trash return 6 Replicates 3 Sampling dates (days 31 Oct. 1996 (1) after harvest) 27 Dec. (58) 6 Mar. 1997 (127) 17 Apr. (169) 28 May (210) 23 July (266) 4 Sept. (309) 8 Oct. (343) 30 Oct. (365) (A) Depth 0-0.05 m. Table 2. Cumulative days, temperature, rainfall, rainy days, and (rainfall--evaporation) at the experimental sites during the experimental period Harwood Mackay Tully Early harvest [SIGMA] Days 347 355 [SIGMA] Temperature (A) 7094 8129 [SIGMA] Rainfall (B) 814 1261 (E) [SIGMA] Rainy days (C) 101 89 [SIGMA] (Rainfall--evaporation) (D) -789 -708 Late harvest [SIGMA] Days 353 344 364 [SIGMA] Temperature (A) 6776 7582 8565 [SIGMA] Rainfall (B) 969 1502 (E) 3694 [SIGMA] Rainy days (C) 112 96 163 [SIGMA] (Rainfall--evaporation) (D) -618 -371 1910 (A) Cumulative mean daily temperature ([degrees]C). (B) Cumulative daily rainfall (mm). (C) Cumulative number of days where rainfall >zero. (D) Cumulative daily (mm). (E) Includes irrigation (70 mm).
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|Author:||Robertson, Fiona A.; Thorburn, Peter J.|
|Publication:||Australian Journal of Soil Research|
|Date:||Feb 1, 2007|
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