4. Opportunities for improved crop management
4.2 Fertiliser use and soil nutrient problems
J
Sugarcane: Research Towards Efficient and Sustainable Production. Wilson JR, Hogarth D M , Campbell JA and Garside AL (Eds).
CSIRO Division of Tropical Crops and Pastures, Brisbane. 1996. pp. 189-193 189 SOIL SURVEY - A TOOL FOR BETTER FERTILIZER MANAGEMENT IN THE AUSTRALIAN SUGAR
INDUSTRY
W O O D A W and BRAMLEY RGV2
'CSR Technical Field Department, PMB 4, Ingham, Q 4850, Australia
2CSlRO Division of Soils, PMB, Aitkenvale, Q 4814, Australia
ABSTRACT
Current fertilizer recommendations for the Australian sugar industry are not soil specific. Consequently they do not take into account important soil properties such as the buffering capacity of soils for added nutrients, the rate of reaction between added nutrients and soils, the rate of biological turnover of nutrients, and interactions between nutrients. Fertilizer application may therefore result in excessive, adequate or insufficient application of nutrients. Excessive application results in inefficient fertilizer use and may also lead to possible detrimental environmental impacts. Conversely, insufficient application will result in sub- optimal crop yields. Thus, both excessive and insufficient fertilizer application may be costly to the industry.
Considerable scope exists for improving the applicability of fertilizer recommendations by taking account of soil characteristics.
This paper describes the results from a detailed soil survey of sugarcane soils in the Herbert River District. Associated physical and chemical analytical data provide the basis for the delivery of soil-specific fertilizer recommendations. This information offers growers the opportunity to improve the precision of their crop nutrition.
INTRODUCTION
The Australian sugar industry currently uses fertilizer recommendations that are industry wide, with no specific recommendations, apart from N, being made for different regions, climatic conditions or soil types (Calcino 1994). Consequently, the recommendations are imprecise as they do not take into account important soil factors such as the ability of soils to retain added nutrients, the rate or magnitude of the reaction between added nutrients and soils, nutrient interactions in different soils, the effects of soil biological activity on nutrient release, and the effects of different rainfall regimes on nutrient movement in soils. Instead, the philosophy has been to base fertilizer recommendations largely on nutrient replacement for optimum crop yields, soil test values or in some cases on sugar price. Critical levels have been derived for most nutrients from the relationship between soil test values and crop response. These are based on an aggregation of trial results from many different regions and soil types.
With increasing emphasis now being placed on the possible detrimental environmental impacts of excessive fertilizer application, a more precise approach to developing fertilizer recommendations for each district based on soil properties is required. Furthermore a recent survey of the behaviour of sugarcane farmers in the Herbert River catchment indicated that m a n y g r o w e r s w e r e d i s s a t i s f i e d w i t h c u r r e n t f e r t i l i z e r recommendations and that 87% of growers were in favour of using soil-specific recommendations (Johnson 1995). These are therefore strong reasons for basing soil management recommendations on the distribution of different soil types in the Herbert.
This paper describes the results from a detailed soil survey which is being conducted in the Herbert River District of north Queensland, and gives examples of ways in which more precise, soil-specific fertilizer recommendations can be developed for the Australian sugar industry.
T H E HERBERT RIVER SOIL SURVEY
A detailed survey of soils used for sugarcane production in the Herbert River district commenced in 1981. Mapping is based on numerous soil observations in every sugarcane field and on soil patterns visible on 1:20,000 colour aerial photographs. Soil maps at a scale of 1:8,000 are then produced (Fig.l). The main criteria used for separating soil types are colour, texture, drainage of top and subsoils and position in the landscape. The purpose has been to convey information to cane farmers, who are the main users of the soil survey information, rather than on correlation with an existing p e d o l o g i c a l l y based system of soil classification such as that of Isbell (1996). Hence, the names of the mapping units are based on simple terms using colour and texture, (eg.
red loam and black organic clay) since these are understandable and recognisable to growers. To date, 24 soils have been delineated and the survey has covered about 35,000 ha, which is approximately 6 0 % of the sugarcane area.
An additional feature of the soil survey is the acquisition of chemical and physical analytical data for each soil type. Samples are taken from the upper cultivated layer (0-100 mm) and from the subsoil below the layer of soil mixing at a number of locations within each mapping unit.
Samples from 720 locations have been analysed for physical and chemical characteristics, using laboratory procedures described by Wood (1986). The data, which are stored in an analytical database, have helped indicate research priorities and areas where further detailed soil characterisation is required.
A major concern when using results from any soil survey is whether the soil mapping units are meaningful in terms of delineating areas which differ in their soil properties and management requirements.
Preliminary results from statistical analysis of soil physical and chemical analyses using discriminant analysis and non-hierarchical cluster analysis support the use of the mapping units as delineating areas of different soils (P. Toscas, CSIRO IPPP Biometrics Unit, personal communication). These results also indicated that it is possible to reduce the number of soil mapping units from 24 to around 5, by clustering soils with similar physical and chemical properties. This has important i m p l i c a t i o n s for t h e d e v e l o p m e n t o f s o i l - s p e c i f i c f e r t i l i z e r recommendations and management practices for growers in the Herbert River District. Instead of having one all-encompassing and possibly imprecise fertilizer recommendation, growers would be able to select fertilizer recommendations which are specific to the soils they are using for sugarcane production.
FERTILIZER MANAGEMENT
Selected mean soil properties from the soil survey database for 3 contrasting soils which occur throughout the district and occupy significant areas are shown in Table 1. All three soils are highly acidic, with mean pH values of 5 or less. Soils with a high clay content in the Herbert are typically high in organic matter, total N, exchangeable Ca and Mg, exchange acidity, cation exchange capacity and extractable Cu and Zn. Conversely, soils with a sandy texture are generally low in organic matter, C E C and both macro and micro nutrients. These differences have important implications for fertilizer management.
Sugar industry N recommendations are based on average response curves for different regions (Chapman 1994). Recommendations are the same for all regions apart from those under full irrigation where
190
Table 1 Selected mean topsail properties (0-100 mm) for 3 of the main mapping units in the Herbert River sugarcane area
Soil type No. of Clay pH water Exch.Ca Exch.Mg Exch. CEC Organic C Total N DTPA DTPA samples acidity extr.Cu extr.Zn (%) (cmol(+)/kg) (cmol(+)/kg) (cmol(+)/kg) (cmol(+)/kg) (%) {%) (mg/kg) (mg/kg)
Clay loam Red loam Coarse sandy loam
16 34 23
34.9 20.6 14.4
4.97 4.83 5.01
2.94 1.16 0.89
1.70 0.35 0.26
2.41 1.65 0.69
7.26 3.38 2.01
0.92 0.68 0.47
0.094 0.058 0.043
1.69 0.56 0.27
2.14 1.10 0.99
higher cane yields are expected. This is in contrast to N fertilizer recommendations in the South African sugar industry which are based on the capacity of each soil type to mineralise N (Meyer & Wood 1994).
Whilst the range of soil organic matter levels in Herbert River soils is narrower than that in South Africa, soil-specific N recommendations based on soil total N (Table 1) can be developed for the Herbert (Wood 1986).
Industry P recommendations are currently based on a soil test which involves dilute acid extraction. However, this test is not a precise indicator of the differing P requirement of cane grown on contrasting soils, as it does not differentiate between soils in terms of their P sorption characteristics as well as less extractive (ie. more sensitive) test such as those based on ion-exchange (Bramley et al, 1995). To increase the precision of P fertilization management so that it takes account of the capacity of the soil to supply P to plants, it has been suggested that P sorption characteristics need to be considered and that the use of one of the less extractive tests for soil P may be appropriate (Bramley et al, 1995). P sorption characteristics have been described for all the main soil types (Wood, 1986) in the Herbert and these have been used to develop soil-specific P fertilizer recommendations (Wood 1988).
I n d u s t r y r e c o m m e n d a t i o n s for l i m e are m a d e o n l y w h e r e soil exchangeable Ca is considered deficient (Calcino 1994). Lime at 5 t/ha is recommended for soils with exchangeable Ca <0.55 cmol(+)/kg, and lime at 2.5 t/ha is recommended for soils with 0.55-1.25 cmol(+)/kg exchangeable Ca. Thus, for the soils in Table 1, lime at 2.5 t/ha would be recommended for the coarse sandy loam and red loam soil types but n o n e for the clay loam, even though mean soil pH is less than 5 and mean exchange acidity amounts to over 3 0 % of C E C . Using these criteria, most of the heavier textured soils in the Herbert River District with higher C E C and exchangeable Ca >1.25 cmol(+)/kg, would never be treated with lime.
T h e emphasis on soil Ca m e a n s that lime recommendations do not address the problem of continuing soil acidification which occurs largely as a consequence of the application of N fertilizer and through the r e m o v a l o f n u t r i e n t s i n h a r v e s t e d c a n e . F u r t h e r m o r e , t h e recommendations fail to account for differences in the nature and rate of reaction between lime and different soil types. To increase precision, it is suggested that lime recommendations need to take into account soil pH, exchangeable aluminium, cation exchange capacity (Table 1) and pH buffering capacity.
Apart from assisting decisions on the amount and frequency of lime a p p l i c a t i o n s n e e d e d on different soil t y p e s , a k n o w l e d g e of soil electrochemical properties and cation and anion exchange capacity is essential for effective fertilizer management especially for soils having a significant amount of pH-dependent charge. Gillman & Sinclair (1987) have shown that it is possible to group soils in north Queensland having similar charge properties and that each group requires different nutrient management. Soil charge characteristics determine the ability of soils to hold onto cations such as Ca, Mg and K and anions such as N 03 and SO4. It has also been demonstrated that the extent of leaching of cations from different sugarcane soils and thus the potential for nutrient loss, c a n b e e x p l a i n e d t h r o u g h a k n o w l e d g e o f soil h y d r a u l i c a n d
electrochemical properties (Gillman et al, 1989), which could also be measured as part of the soil survey.
Where soils have a low CEC, such as the coarse sandy loams (Table 1), careful nutrient management is essential. If soils b e c o m e too acidic then acidic cations (H + Al) dominate the exchange complex leaving insufficient exchange capacity for essential nutrients like Ca, Mg and K. In cases of extremely low C E C , it may not be possible to achieve the Industry "critical levels" for exchangeable cations on which current r e c o m m e n d a t i o n s for lime, Mg and K application are based. With industry recommended levels for Ca. Mg, and K being 1.25, 0.25 and 0.24 cmol(+)/kg respectively (Calcino 1994), the mean C E C of the coarse sandy loams (Table 1) is only slightly higher than the sum of these levels. It may be more appropriate to base recommendations on the proportion of the C E C occupied by each nutrient so that imbalances of one nutrient over another are avoided and differences in charge characteristics between soil types are taken into account. Fertilizer management strategies should also acknowledge that large nutrient applications are not appropriate on low C E C soils. If they do not, then wastage of fertilizer and off-farm environmental impacts are the likely consequences.
Industry recommendations for minor element nutrition are not well developed apart from Zn which is based on an acid extraction soil test.
Reghenzani (1993) has noted that it is possible to group soil types in north Queensland on the basis of their potential for Zn deficiency.
However, in view of the lack of precision in relating crop response to soil test data and the limited knowledge of the role of other minor elements such as Cu, B and Mo in sugarcane nutrition, it is sensible to apply small maintenance quantities of minor elements as part of all fertilizer p r o g r a m m e s and to ensure that these elements are applied in situations where soil micronutrient levels are low (as on most sandy soils in the Herbert) and where lime is to be used, as an increase in soil pH will further restrict the availability of some micronutrients.
C O N C L U S I O N S
T h e basis on which fertilizer recommendations are m a d e for Australian sugarcane producers has not changed m u c h over the last 50 years. With increasing concern being shown by the Industry for the minimisation of off-farm impacts of fertilizer use, a different approach is needed for fertilizer management. A regional approach to nutrient m a n a g e m e n t based on soil properties should maximise long-term profitability whilst minimising nutrient losses from the farm.
T h e existence of a detailed soil survey in the Herbert River district coupled with a comprehensive soil analytical database should enable soil-specific fertilizer management strategies to be developed which c a n be p r o g r e s s i v e l y refined as m o r e i n f o r m a t i o n a b o u t n u t r i e n t availability and retention is obtained.
A C K N O W L E D G M E N T S
We thank Ron Rutherford and Sam Pennisi for conducting the soil survey and Jenny Hart for coordinating the physical and chemical analysis of soil samples.
Detail from the CSR Soil Survey for the area around Macnade Mill.
c Clay cl Clay Loam csl Coarse Sandy Loam fsl Fine Sandy Loam rl Red Loam rb River Bank ro River Overflow rs River Sand sc Slty Clay tz Terrace Sit
Unassfgned/Rlparlan/Urban
193 REFERENCES
Bramley RGV, Wood AW, Cristaudo R (1995) Improving the precision of p h o s p h o r u s fertilizer r e c o m m e n d a t i o n s for sugar c a n e . Proceedings Australian Society of Sugar Cane Technologists, pp.
179-186.
Calcino DV (1994) Australian Sugarcane Nutrition Manual. SRDC/
BSES, Indooroopilly, Qld.
Chapman LS (1994) Fertilizer N management in Australia. Proceedings Australian Society of Sugar Cane Technologists, pp. 83-92.
Gillman GP, Sinclair DF (1987) The grouping of soils with similar charge properties as a basis for agrotechnology transfer. Australian Journal of Soil Research, 25, 275-285.
Gillman GP, Bristow KL, Hallman MJ (1989) Leaching of applied c a l c i u m a n d p o t a s s i u m from an O x i s o l in h u m i d tropical Queensland. Australian Journal of Soil Research, 27, 183-198.
Isbell R (1996) The Australian Soil Classification, Volume 4, Australian Soil and Land Survey Handbook Series, CSIRO Publishing,
Melbourne.
Johnson AKL (1995) Risk perceptions and nutrient management responses in the Australian sugar industry: preliminary results from the Herbert River District. Proceedings Australian Society of Sugar Cane Technologists, pp. 172-178.
Meyer JH, Wood RA (1994) Nitrogen management of sugar cane in South Africa. Proceedings Australian Society of Sugar Cane Technologists, pp. 93-104.
Reghenzani JR (1993) A survey of the nutritional status of north Queensland sugarcane soils with particular reference to zinc.
Proceedings Australian Society of Sugar Cane Technologists, pp.
298-304.
Wood AW (1986) Soil surveys as an aid to better soil management in the Herbert valley. Proceedings Australian Society of Sugar Cane Technologists, pp. 49-54.
Wood AW (1988) Phosphate sorption characteristics of sugarcane soils in the Ingham area. Proceedings Australian Society of Sugar Cane Technologists, pp. 111-118.
Sugarcane: Research Towards Efficient and Sustainable Production. W i l s o n JR, H o g a r t h D M , C a m p b e l l JA and G a r s i d e AL ( E d s ) . 194 C S I R O Division of Tropical C r o p s and Pastures, B r i s b a n e . 1996. p p . 194-197
SPLITTING N FERTILISER APPLICATION - DOES IT INCREASE PRODUCTION EFFICIENCY OF SUGARCANE?
C H A P M A N L S
Bureau of Sugar Experiment Stations, Private Mail Bag 57, Mackay Mail Centre Q 4741 Australia
A B S T R A C T
Sugar yield was not increased by applying sulfate of ammonia in two or three applications compared to a single application, on ratoon crops of sugarcane, with a green cane trash blanket. Split applications also had no effect on N uptake by the crop, efficiency of N fertiliser use and residual N levels in soil. Apparent recovery of fertiliser N was mostly in the range of 20-35% and not increased by split applications. These results were obtained from three experiments conducted on duplex soils and one on a gradational soil, near Mackay. Sulfate of ammonia was surface banded on cane rows at rates up to 300 kg N/ha in three experiments, while ,!N labelled sulfate of ammonia was buried in cane rows at 160 kg N/ha in the fourth experiment.
INTRODUCTION
Australian canegrowers usually fertilise their ratoon crops of sugarcane with a nitrogen/phosphorus/potassium mixture in one application at 0- 3 months after harvesting. Two applications are usually made to plant crops, which receive a mixture at planting, followed by a sidedressing of N fertiliser at about 2-3 months later at stooling.
Bureau Sugar Experiment Station extension advice is to delay fertilising ratoon crops until a new root system has developed and the crop is 0.5 m high. This can increase yield above that of fertilising immediately after harvesting (Calcino & Burgess 1995) which is probably due to better utilisation of N. Utilisation of N fertiliser by a sugarcane crop is usually low with 20- 4 0 % of the N applied utilised by the crop in the year of application (Chapman et al 1994; Vallis et al 1995). The N reserve in soil, mostly in organic form, is an important source of N for the crop. Keating et al (1993) reported that between 59 and 7 6 % of the N found in cane crops in south Queensland and north New South Wales could be attributed to N mineralised from this source. A proportion of the fertiliser N does replenish this soil organic pool, with typical values of 2 6 % of fertiliser N being found in soil organic matter 12 months after application (Chapman et al 1994; Vallis et al 1995).
Canegrowers are concerned about the low utilisation of N fertilisers by the crop, because of the additional costs of unused fertilisers, and the possibility that fertiliser losses may lead to adverse downstream effects
An objective of this research was to increase the efficiency of utilisation of N fertiliser. Synchronisation of N applications to match crop uptake is one likely strategy to increase the efficiency of N use. This report presents data from experiments conducted to evaluate the following issues: can splitting of N applications reduce the fertiliser applied without affecting yield; can splitting fertiliser applications improve the N uptake by the crop?
M E T H O D S Treatments
T h e four different split-N fertiliser trials, each with four replicates of the fertiliser t r e a t m e n t s , w e r e c o n d u c t e d on ratoon crops at three sites. T h r e e trials h a d a p p l i c a t i o n r a t e s o f 0 , 100, 2 0 0 and 3 0 0 k g N / ha as sulfate of a m m o n i a b a n d e d on t o p of the trash in the c a n e row.
N fertiliser w a s applied either as single, t w o (split-2) or three (split- 3) applications at 4, 4 and 10, or 4, 10 and 16 w e e k s after r a t o o n i n g , respectively. T h e 3 0 0 kg N / h a rate in Expt. 1 and 2 w a s applied only as a single application, while the split-3 t r e a t m e n t s w e r e included for this r a t e in Expt. 3(a).
The proportion of fertiliser applied at each time was: 0.25, 0.75 for split-2, and 0.25, 0 . 5 0 , 0 . 2 5 for split-3 for Expts. 1 and 2; 0.50, 0.50 for split-2, and 0.33, 0 . 3 3 , 0.33 in Expt. 3(a). Adjacent to Expt. 3(a) was Expt. 3(b) which had 15N labelled sulfate of ammonia at 160 kg N/ha buried 100mm deep in a band in the cane row. This fertiliser was applied
as single or split-3 applications with the proportion in each split being 0.33 applied at 4, 10 and 16 weeks after ratooning.
Sites
T h e e x p e r i m e n t s w e r e conducted a t three locations near M a c k a y (149.21°E, 21.46°S). Soil types were: Expt. 1 - brownish black, sandy loam, topsoil with reddish brown, sandy clay loam, subsoil (Typic Ustochrept); Expt. 2 - greyish yellow, sandy loam, topsoil with yellow, sandy clay, subsoil (Typic Haplustalf); Expts. 3(a) and (b) - brown, sandy clay loam, topsoil with brown mottled m e d i u m clay, subsoil (Typic Haplustalf). All sites had trash mulches retained from green- cane harvesting, and this practice had been in place respectively for 2, 1 and 4 years for Expts 1, 2 and 3 prior to the treatments being applied.
Total rainfall for the experiments w e r e 840, 3 1 9 3 a n d 1293 m m , respectively. All experiments were irrigated as required for commercial cane production, and after each fertiliser application to activate fertiliser if rain was insufficient for this purpose.
Soil mineral N
In Expt. 1 and 2, soil was sampled by coring 5 0 m m diameter by 300 mm depths at 4, 10, 16, 22 and 52 w e e k s after ratooning. Soil samples were extracted with 2M KC1 and analysed for NO3 plus NO2 (Best 1976) and NH4 + (Rowland 1983) in Expt. 1 and 2. In Expt. 3(b) soil was excavated to 3 0 0 mm and cored, 5 0 m m diameter to 1.2 m depth.
Samples provided measurements of N 03- plus N 02- and NH4 + as above, total N (Bremner & Mulvaney 1982) and 1SN. by steam distillation of digests (Saffigna & Waring 1977), and isotope ratio (Ross & Martin 1970). Measurements were conducted at 10, 16. 22 and 52 weeks after ratooning.
N in crop
In Expts. 1 and 2, crop yield was measured at 10, 16 and 22 weeks after ratooning by multiplying the average weight of 10 stalks by total number of stalks. At harvest after 52 weeks, yield of cane was measured by weighing mechanically cut billets from an area of 68m2. In Expt. 3(b), only cane from a 0.75 m section of the 15N treated areas w a s used for measuring N uptake at 10, 16, 22 and 52 weeks. All cane was harvested, weighed, ground, subsampled and analysed for moisture, total N and
15N. Biomass was partitioned into stalks, tops and trash at 10, 16, 22 and 52 weeks after ratooning. Total N in the crop was divided by the cane yield at harvest to give a measure of the efficiency of N usage. N uptake for the non-fertilised treatments in Expts 1, 2 and 3(a) w a s subtracted from N uptake of the fertilised treatments to give a measure of N uptake which could be attributed to fertiliser. This was compared with the fertiliser applied to give a measure of apparent fertiliser N recovered by the crop. Sugar yield at harvest was determined as the product of cane yield by CCS measured in juice crushed from 6-stalk samples.
R E S U L T S Sugar yield
N fertiliser applications significantly increased sugar yields by 3 . 4 , 4 . 8 and 5.5 t/ha for Expts. 1, 2, and 3(a) respectively. M a x i m u m yields were