Journal of Plant Nutrition

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Significant Nitrogen by Sulfur Interactions Occurred for Canola Grain Production and Oil Concentration in Grain on Sandy Soils in the Mediterranean-Type Climate of Southwestern Australia R. F. Brennan a; M. D. A. Bolland b a Department of Agriculture and Food, Albany, Australia b Department of Agriculture and Food, Bunbury, Australia Online Publication Date: 01 July 2008 To cite this Article: Brennan, R. F. and Bolland, M. D. A. (2008) 'Significant Nitrogen by Sulfur Interactions Occurred for Canola Grain Production and Oil Concentration in Grain on Sandy Soils in the Mediterranean-Type Climate of Southwestern Australia', Journal of Plant Nutrition, 31:7, 1174 — 1187 To link to this article: DOI: 10.1080/01904160802134459 URL: http://dx.doi.org/10.1080/01904160802134459

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Journal of Plant Nutrition, 31: 1174–1187, 2008 Copyright © Taylor & Francis Group, LLC ISSN: 0190-4167 print / 1532-4087 online DOI: 10.1080/01904160802134459

Significant Nitrogen by Sulfur Interactions Occurred for Canola Grain Production and Oil Concentration in Grain on Sandy Soils in the Mediterranean-Type Climate of Southwestern Australia R. F. Brennan1 and M. D. A. Bolland2 1 2

Department of Agriculture and Food, Albany, Australia Department of Agriculture and Food, Bunbury, Australia

ABSTRACT The nitrogen (N) by sulfur (S) interaction for canola (Brassica napus L.) grain production and oil concentration in grain has been quantified in temperate climates, but it is not known if these results also apply to sandy soils common in the Mediterranean-type climate of southwestern Australia where canola is now a major crop. Seventeen field experiments were undertaken with canola in the region during 1994 to 2005 in which 4 rates of both N (0–138 kg N/ha) and S (0–34 kg S/ha) were applied. Significant grain yield responses to applied N occurred in all experiments and the responses increased as more S was applied. Grain yield responses to applied S only occurred when N was applied and tended to increase as more N was applied. When no S was applied the two largest rates of N applied, 69 and 138 kg N/ha, induced S deficiency reducing grain yields. The oil concentration in grain tended to decrease as more N was applied and increased as more S was applied, particularly when the two largest rates of N were applied. Consequently significant N × S interactions were obtained in all experiments for grain production and in 15 experiments for oil concentration in grain. Keywords: Canola, nitrogen, sulfur, nitrogen by sulfur interaction, sandy soils, oil concentration in grain

INTRODUCTION Since the early 1990s canola (Brassica napus L.) has become a major crop grown in rotation with spring wheat (Triticum aestivum L.) and narrow-leaf Received 23 April 2007; accepted 8 August 2007. Address correspondence to R. F. Brennan, Department of Agriculture and Food, 444 Albany Highway, Albany, WA 6330, Australia. E-mail: [email protected] 1174


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lupin (Lupinus angustifolius L.) on sandy soils common in the Mediterraneantype climate of southwestern Australia. Most of the soils are invariably nitrogen (N) deficient for canola grain production, so large grain yield responses to applied N are common (Mason, 1998a). However, sulfur (S) deficiency for canola grain production only occurs on some very sandy soils (Brennan and Bolland, 2006). Consequently, the fertilizer N requirements of canola in the region have been determined but when adequate fertilizer S (∼20 kg S/ha) was also applied (Brennan et al., 2000). Likewise, the S requirements for canola grain production in the region has been determined on S deficient sandy soils but when adequate fertilizer N (∼70 kg N/ha) was also applied (Brennan and Bolland, 2006). Consequently, the NxS interaction for canola grain production on these soils is not known. Research done elsewhere on better soils in temperate climates has shown that increasing the amounts of N fertilizer decreased canola grain yields when S was deficient (Janzen and Bettany, 1984; Zhao et al., 1993; McGrath and Zhao, 1996). Further research done elsewhere in temperate climates using a variety of crop species, have shown significant NxS interactions for grain production (mustard, Aulakh et al., 1980; wheat, Randall et al., 1981) and grain quality (protein or oil concentration in grain) (wheat, Beyers and Bolton, 1979; canola, McGrath and Zhao, 1996). The NxS interaction has been attributed to the requirements of both N and S in nitrate reductase (Friedrich et al., 1977) and protein synthesis (wheat, Stewart and Porter, 1969; canola, McGrath and Zhao, 1996). Field studies on N and S deficient soils showed that applications of N when no S was applied reduced grain yields, whereas application of S alone produced no grain yield responses (Brassica campestris L, Nyborg et al., 1974; canola, McGrath and Zhao, 1996). We report the results of 17 field experiments from 1994 to 2005 to establish whether the findings of previous N × S interaction studies conducted on better soils in temperate climates also applied to canola grown on sandy soils in the Mediterranean-type climate of southwestern Australia. In addition, in 10 of the 17 experiments the concentrations of S and the N:S ratio in canola shoots at two early growth stages, rosette and flower buds visible, were related to grain production to define critical S concentrations or N:S ratios in shoots to indicate when reductions in canola grain production due to S deficiency were likely. MATERIALS AND METHODS Field Experiments All 17 experiments were undertaken from 1994–2005 on sandy soils in the Mediterranean-type climate of southwestern Australia, with a cool, wet lateApril to mid-November growing season, and a mostly hot and dry December to March. Each experiment was for one year only. There was one experiment in 1994, four in 1995, two in 1996, two in 2001, four in 2003, one in 2004, and three in 2005.


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Sulfur deficient soils were selected for the field experiments. The potassium chloride (KCl)-40 procedure of Blair et al. (1991) is the standard soil S test used in southwestern Australia and is for the top 10-cm of soil. However, as described in detail by Brennan and Bolland (2006), many sandy soils in the region are S deficient in the top 10-cm of soil, but canola crops frequently access enough S in the subsoil for grain production so soil test values below 10-cm are required to indicate likely S deficiency for canola grain production. Consequently, based on results of Brennan and Bolland (2006), 17 sites were selected with KCl-40 soil test values ≤7 mg/kg in the top 30-cm of soil for our experiments to ensure S deficiency was highly likely for canola grain production. All 17 field experiments comprised 4 rates of N, and for each rate of N, there was also four rates of S, arranged in a completely randomized block, replicated three times. The four rates of N applied in all 17 experiments were 0, 35, 69, and 138 kg N/ha, as urea (46% N). The four rates of S applied in the 7 experiments done from 1994–1996 were 0, 6, 13, and 25 kg S/ha, and in the 10 experiments done from 2001–2005 were 0, 9, 17, and 34 kg S/ha. In all 17 experiments, S was applied as gypsum (CaSO4 2H2 O, 17% S) obtained from a deposit near Wyalkatchem, Western Australia. Most crops on sandy soils in southwestern Australia are now sown using notill. Consequently, our experiments were sown using no-till, in which stubbles of the previous crops are retained and crops are sown with minimal soil disturbance using very narrow tines and weeds are controlled before and after sowing using herbicide sprays (Jarvis, 2000). For the seven experiments done from 1994– 1996, plots were 1.44 m wide and 40 m long, with a 0.4 m untreated area between each plot. Eight rows of seed, 18-cm apart, were sown down each plot. After 1997, plots were 1.5 m wide and 25–30 m long, with a 0.4 m untreated area between each plot. Six rows of seed, 22.5 cm apart, were sown down each plot. These were the row widths used in the different years for sowing no-till canola crops in the region. Canola seed was sown at 4–5 kg/ha approximately 2 cm deep, the standard recommendation to sow canola in southwestern Australia (Carmody, 1999). The following basal fertilizers were applied to ensure N and S were the only nutrient elements limiting canola production: i) Placed (drilled) with canola seed while sowing, 30 kg phosphorus (P)/ha and 24 kg calcium (Ca)/ha as triple superphosphate (20% P, 16% Ca, 450 mm) areas, it is recommended to apply these elements



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to canola crops 4–6 weeks after sowing when sufficient crop roots have been developed to take up the applied elements (N and S, Mason, 1998a; 1998b; K, Edwards, 1998). The recommended canola cultivar was used (as listed in the Western Australian Department of Agriculture sowing guides from 1994–2004). Narendra was the cultivar used in experiments before 1996. Triazine tolerant canola cultivars were used thereafter: Karoo in 1996, Pinnacle in 2001, Surpass 501 in 2003 and 2004, and Stubby and Tornado in 2005.

Measurements Sites for the experiments were selected in March of the year each experiment started when soil samples from the sites were collected to 30 cm depth at 30 random locations. The samples were separated into the following profile depths: 0–10, 10–20, and 20–30 cm. The 30 samples from each profile depth at each site were bulked and subsamples of the air-dry bulked samples were used to measure KCl-40 soil test S (Blair et al., 1991). In the procedure, soil samples were mixed with 0.25 M KCl heated at 40◦ C for 3 h and the concentration of S in the extract was measured using inductively coupled plasma-atomic emission spectroscopy (ICP-AES, Matilainen and Tummavuori, 1996). Canola shoot yields were measured in 10 of the 17 experiments by cutting plants at ground level from two rows of plants, each 1 m long, from 5 random positions within each plot. Plants were sampled at the rosette stage (GS2.0; Sylvester-Bradley, 1985) and flower buds visible stage (GS3.3). Plant samples were oven dried at 70◦ C for three days and weighed. After weighing, the dried shoots were ground and subsamples of ground shoots were used to measure concentration of S in the dried shoots using procedures described by Tabatabai and Bremner (1970). Further, subsamples of dried ground shoots were used to measure concentration of N in tissue using the Kjeldahl procedure described by McKenzie and Wallace (1954). Canola grain yields were measured by machine harvesting grain from each whole plot, excluding the two outside rows, and the harvested grain was weighed. Subsamples of the harvested grain were used to measure concentration of oil and moisture in grain as outlined by AOCS (1997). Grain yields and the oil concentrations in grain were corrected to 6% moisture content of grain.

Analysis of Data Analysis of variance was used to compare means of treatments using GenStat (2005). The relationship between grain yield, expressed as a percentage of the maximum (relative) yield, and concentration of either S in shoots or the N: S


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ratio in shoots was used to determine critical tissue test values, which were the tissue test values that were related to 90% relative grain yields (Ulrich and Hills, 1967). Data used were for the two largest rates of N applied, 69 and 138 kg N/ha, because these treatments included the typical amounts of N applied to canola crops in southwestern Australia (Carmody, 1999). The relationship between relative grain yield and the concentration of S in shoots at GS2.0 and GS3.3 were adequately described by an exponential (Mitscherlich) equation: y = a + b exp(−cx)

(1)

Where y was the relative yield (%), x was the concentration of S in shoots (g/kg), and a, b, and c were coefficients. Mean data were fitted to the equation by non-linear regression using GenStat (2005). The concentration of S in the dried shoots that was related to 90% of the maximum yield was calculated using the exponential equation (1) fitted to the data, and is defined as the critical S concentration in the dried shoots below which grain yield decreases due to S deficiency are likely. The relationship between relative grain yield and the N: S ratio measured in shoots at GS2.0 and GS3.3 was adequately described by a linear equation (GenStat, 2005): Y = A + Bx

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Where Y was the relative grain yield (%), x was the N: S ratio in shoots, and A and B were coefficients. The fitted equations were then used to calculate the N:S ratio that was related to 90% of the maximum grain yield, defined as the critical N:S ratio in shoots, above which grain yield decreases due to S deficiency are likely.

RESULTS Yield Responses to Applied Nitrogen and Sulfur Only grain production data are presented because results for shoots and grain were similar and grain production is economically more important. Grain yield responses to applied N occurred in all experiments, and were larger when the first 2 levels of S were applied (Figures 1 and 2). For the two largest rates of N applied (69 and 138 kg N/ha), grain yields were similar and on the maximum yield plateau of the relationship when the 2 largest rates of S were applied (Figures 1 and 2). When no N was applied, no significant responses to applied S occurred. Grain yield responses to applied S only occurred when N was applied and reached a maximum yield plateau when 13 kg S/ha was applied in experiments 1–7 or 17 kg S/ha was applied in experiments 8–17 (Figures 1 and

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2). Increases were 25–34% when 69 kg N/ha were applied and 40-59% when 138 kg N/ha were applied. Application of 69 and 138 kg N/ha when either no S or the smallest rate of S (6 or 9 kg S/ha) was applied reduced grain yields (Figures 1 and 2). Therefore, the effect of applied N and S on shoot and grain yields, and the N × S interaction, were significant in all experiments.

Oil Concentrations in Grain For all four rates of S applied the consistent trend was for oil concentrations in grain to decrease as more N was applied (Figure 3). Increasing application of N from 69 to 138 kg N/ha decreased concentrations of oil in grain by an average

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R. F. Brennan and M. D. A. Bolland (a) Experiments 1–7

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of about 2.5 percentage points where no S fertilizer was applied compared with about 1.0 percentage point when 25 or 34 kg S/ha was applied. Overall, the decrease in oil concentration as more N was applied was smaller as more S was applied. When no N was applied, increases in oil concentration in grain as more S was applied were small, about 0.2 percentage points. Therefore, for oil concentration in canola grain, the effect of applied N and S, and the N × S interaction, were significant in 15 of the 17 experiments. Only N significantly affected concentration of oil in grain in experiments 4 and 15.

Critical Tissue Test Values Concentrations of S and the N: S ratio in shoots that were related to 90% of the maximum grain yield (critical values) declined as plants matured. At the rosette stage (GS2.0) the critical S concentration in shoots was 6.0 g/kg (Figure 4a), and declined to about 4.4 g/kg at the flower buds visible growth stage (GS3.3) (Figure 4b). Similarly the N: S ratio at GS2.0 was 9.5 (Figure 5a), compared with about 8.0 at GS3.3 (Figure 5b).

DISCUSSION As found in previous studies in southwestern Australia, significant grain yield responses to applied N occurred in all experiments. The results of our experiments on sandy soils in the Mediterranean-type climate of southwestern Australia were consistent with results of previous studies conducted on better soils in temperate regions summarized in the Introduction: • There was a significant N × S interaction for canola grain production in all 17 experiments. • There was a significant N × S interaction for oil concentration in canola grain in 15 experiments, with significant effects on oil concentrations in grain due to N only in two experiments. • Grain yield responses to applied N were smaller when zero S or low rates of S were applied. • Grain yield responses to applied S only occurred when N was also applied. • When no S or the lowest rates of S (13 or 17 kg S/ha) were applied, the highest N treatments (69 and 138 kg N/ha) induced S deficiency reducing grain yields. • The oil concentration in canola grain was unaffected by level of S applied when no N was applied. However, when N was applied, the concentration of oil in canola grain increased as more S was applied, particularly when the higher rates of N were applied (69 and 138 kg N/ha).

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Figure 3. Mean data for the relationship between oil concentration in canola grain and the rate of N applied for (a) experiments 1 to 7 when 0 (), 6 (), 13 () and 25 () kg S/ha was applied, and (b) for experiments 8 to 17 when 0 (), 9 (), 17 () and 34 () kg S/ha was applied. The l.s.d.s (P = 0.05) as % were 0.2 for (a) and 0.3 for (b).

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• Application of increasing amounts of N at all sites consistently reduced concentration of oil in canola grain. Sulfur deficient sites were wanted for this study. Based on the results of our previous study (Brennan and Bolland, 2006), sites for this study were selected with soil test S values ≤7 mg/kg in the top 30 cm of soil and obtained grain yield responses to applied S in all 17 experiments. It is therefore recommend that rather than relying on shallow soil testing or tissue testing presently used in the region, soil testing to 30 cm depth be used to indicate when S deficiency is likely to reduce canola grain production on the predominant sandy soils of the region. For concentration of S measured in shoots at GS2.0 and GS3.3, the critical values we obtained agree with values reported in previous papers (Zhao et al., 1993; Withers and O’Donnell, 1994; McGrath and Zhao, 1996; Pinkerton, 1998). Critical values for the N: S ratio of 9.5 at GS2.0 and 8.0 at GS3.3 were obtained, compared with the 9.5 critical value obtained by McGrath and Zhao (1996) at GS4.0. Therefore, our critical N: S values for earlier growth stages were similar or lower than the critical N: S values obtained at a later growth stage by McGrath and Zhao (1996). This may be because McGrath and Zhao (1996) applied a maximum of 230 kg N/ha, compared with the maximum of 138 kg N/ha we used.

ACKNOWLEDGMENTS Funds were provided by the Government of Western Australia and by the Grains Research and Development Corporation (project number DAW0075). Experiments from 1994–1996 were conducted by M.G. Mason. Technical assistance was provided by T. D. Hilder, R. J. Lunt, J. Majewski, and F. M. O’Donnell. Soil and plant chemical analyses were done by chemists of the Chemistry Centre (WA).

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