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SOIL FERTILITY

Sugarcane Response to Phosphorus Fertilizer in Relation to Soil Test Recommendations on Everglades Histosols

^a USDA-ARS Sugarcane Field Station, HCR Box 8, Canal Point, FL 33438 USA
^b Florida Crystals, P.O. Box 86, South Bay, FL 33493 USA

bglaz{at}ag.gov

	ABSTRACT

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
To protect habitat in the Everglades, legislation mandates a reduction of at least 25% in the P content of water discharged from the Everglades Agricultural Area (EAA). Accurate P fertilizer recommendations for sugarcane (interspecific hybrids of Saccharum spp.), the major crop in the EAA, are needed to help achieve this P reduction. The objective of this study was to compare two soil-tests for basing P fertilizer recommendations for sugarcane grown on Histosols in the EAA. Three yield characteristics were measured at four field locations with no added P (P0), an often-recommended commercial rate of 24 kg P ha^-1 (P1), and 48 kg P ha^-1 (P2) for the plant-cane, first-ratoon, and, at three locations, the second-ratoon crop. One group of eight genotypes was planted at two locations, and two other groups of eight genotypes were each planted at one of two other locations. An acetic acid-extractable P (Pa) soil test predicted yields better than the water-extractable P (Pw) test. However, unexpected responses in sugar and cane yields occurred for both P extraction procedures. Further knowledge of the effects of soil pH, factors affecting P mineralization, and sugarcane genotype response to P may explain some of the unexpected results.

Abbreviations: BMP, best management practice • EAA, Everglades Agricultural Area • P0, no P fertilizer • P1, 24 kg P ha^-1 • P2, 48 kg P ha^-1 • Pa, acetic acid-extractable P • Pw, water-extractable P • STAs, Storm Water Treatment Areas • TCH, metric tons of cane ha^-1 • TRS, theoretical recoverable sugar measured as g sugar kg^-1 cane • TSH, metric tons of sugar ha^-1

	INTRODUCTION

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
THE EAA is a 280000 ha agricultural basin of Histosols in southern Florida. About 144000 ha of sugarcane are grown in the EAA (Glaz, 1998). Legislation mandates that the P content of water discharged from the EAA be reduced by at least 25% from the baseline mean calculated using 1978 through 1988 data (Whalen and Whalen, 1994). This is one of several measures aimed at sustaining much of the unique habitat characteristic of the predrained Everglades. In addition, about 16000 ha in the EAA are being converted from agriculture to specially designed artificial wetlands to serve as Storm Water Treatment Areas (STAs) (Stone and Legg, 1992). Water released from the STAs must have its P concentration reduced to no more than 50 µg L^-1 by 2002 (Walker, 1996). In addition, the legislation included options for further research to determine if levels lower than 50 µg P L^-1 would be necessary to restore the ecologic health of the Everglades. Since then, research has documented changes in natural populations of Everglades flora and fauna at P concentrations greater than 10 µg P L^-1 (McCormick et al. 1999).

Farmers in the EAA are successfully using an extensive BMP program to meet P-reduction requirements (Stone and Legg, 1992; Whalen and Whalen, 1994; Izuno and Capone, 1995). Stone and Legg (1992) estimated that the cost of BMP implementation was $153 ha^-1 and annual operation and maintenance costs were about $9 ha^-1. A BMP approved for EAA farmers is to apply P fertilizers according to a calibrated soil test. Since the inception of this BMP, most EAA sugarcane farmers have complied by using a water soluble test for labile P (Pw) (Sanchez, 1990). The criteria for the P fertilizer recommendations from the Pw test were reported by Gascho and Freeman (1974) and Gascho and Kidder (1979). One major sugarcane grower chose the Bray 2 soil extractant (Bray and Kurtz, 1945) in 1958 because compared with Pw, it removed more of the acid-soluble and adsorbed P (Andreis and McCray, 1998).

Some EAA farmers have recently shown interest in Pa, a soil test that measures acetic acid-extractable P (Korndörfer et al., 1995). Due to its acid extraction, it is expected that Pa measures labile and reserve P. The Pw procedure often provides acceptable results for vegetable crops in the EAA that have a substantially shorter growing season than sugarcane. With the 8 to 14 mo growing season of sugarcane, several workers believe that a measure of reserve P such as the Bray 2 or Pa would provide better calibrations.

Korndörfer et al. (1995) reported that Pa predicted cane and sugar yield responses to P better than Pw. However, their analyses were based on what are now outdated or minor cultivars on EAA Histosols. Also, they did not report P responses by crop year (plant crop and ratoons) and they did not test responses of theoretical recoverable sugar. The objective of this study was to compare, for the plant and two ratoon crops, P fertilizer recommendations determined by Pw and Pa for major and promising sugarcane genotypes grown on Histosols in the EAA.

	Materials and methods

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
Responses to three rates of P fertilizer were determined for 24 sugarcane genotypes. Eight genotypes were field tested at two locations, and two other groups of eight genotypes were each tested at one of two other field locations. All four locations were in Palm Beach County, FL. Location 1 was at the 20 Mile Bend Farm of Sugar Farm Cooperative, Eastern Division. This farm is in the eastern region of sugarcane production in the EAA, about 12 km west of West Palm Beach, FL. Locations 2, 3, and 4 were at the Okeelanta Corp., about 6 km north of the southern border of sugarcane production in Palm Beach County.

All four experiments were conducted on Histosols typical of the EAA. These soils often contain more than 85% organic matter (Zelazny and Carlisle, 1974) comprised primarily of decomposed sawgrass (Cladium jamaicense Crantz). The experiment at Location 1 was on a Terra Ceia muck (euic, hyperthermic Typic Medisaprist). The experiments at Locations 2, 3, and 4 were on Dania muck soils (euic, hyperthermic shallow Lithic Medisaprist). As described by McCollum et al. (1976), the distinguishing characteristic between a Dania and Terra Ceia muck is depth of soil over limestone rock. The thickness of the organic layer is >130 cm in a Terra Ceia muck and <51 cm in a Dania muck.

Treatments in all experiments were arranged in randomized complete-block designs with four replications. Each experiment had two factors, sugarcane genotypes and P fertilizer rates. Fertilizer rate zero, P0, was no P fertilizer; P1 was an often-recommended commercial rate of 24 kg P ha^-1; and P2 was 48 kg P ha^-1. These fertilizer treatments were applied in each crop year of each experiment; applications were made in the furrow at planting and topdressed in a band adjacent to each row in ratoon crops. All P was applied as triple superphosphate. Fertilizer application dates are shown in Table 1 . These dates were similar to commercial fertilizer application dates for the fields containing each experiment.

Soil samples from the top 20 cm of soil were collected soon after planting in each replication from two plots that were not fertilized with P at Locations 1, 2, and 3. At Location 4, soil samples were collected before planting from the 24-ha field that contained the experiment. The samples were analyzed for pH (Sanchez, 1990), Pw (Sanchez, 1990), and Pa (Korndörfer et al. 1995) by the University of Florida/Institute of Food and Agricultural Sciences, Everglades Research and Education Center Soil Testing Laboratory, Belle Glade.

The eight genotypes at Locations 1 and 2 were `CL 72-321', `CL 61-620', `CP 72-2086', `CP 73-1547', `CP 80-1827', `CP 81-1254', `CP 85-1308', and `CP 85-1382'. The eight genotypes planted at Location 3 were `CL 73-239', `CP 70-1133', `CP 72-1210', `CP 78-1628', `CP 80-1743', `CP 84-1198', `CP 85-1432', and `CP 85-1491'. At Location 4, the eight genotypes were `CP 88-1508', `CP 88-1762', CP 90-1113, CP 90-1428, CP 90-1464, CP 90-1535, CP 90-1549, and CP 92-1435.

The most important yield characteristic of sugarcane is t sugar ha^-1 (TSH). There are two major components of TSH. One component is theoretical recoverable sugar (TRS), measured as g sucrose kg^-1 of cane. The other component of TSH is t cane ha^-1 (TCH). The product of TRS and TCH divided by 1000 equals TSH. To calculate TRS, samples consisting of 10 stalks were collected from each plot. Dates of these samples are listed in Table 1. To choose stalks, a starting point was selected from one of the middle two rows of each plot, and from that starting point, the next 10 mature stalks were collected. Since sugarcane grows in large stools of primary, secondary, tertiary, etc. stalks, this sampling procedure helps collect a representative mixture of stalks.

TRS was calculated from the Brix and pol of each sample using a previously described procedure (Legendre, 1992). As described by Meade (1963)(p. 625), Brix represents the apparent solids in a sugar solution and is measured as a percentage. It was measured with a refractometer that automatically corrected for temperature. Pol, as described by Meade (1963)(p. 625), was the value obtained from polarization of the sugar solution in a saccharimeter. No units were given for pol by Meade (1963)(p. 625). TCH was calculated by multiplying stalk number by stalk weight. Stalk weight was measured from the same sample of 10 stalks used to calculate TRS. Dates on which stalk counts were conducted are shown in Table 1.

Analyses of variance were calculated by using PROC GLM of SAS (SAS Inst., 1985). The analyses were calculated as split plots in time (crop years) arranged in randomized complete-block designs with two factors (genotypes and P fertilizer rates). The REPEATED statement (SAS Inst., 1985) was used to calculate the repeated observations by crop. Genotypes and P fertilizer rates were evaluated as fixed effects. Preplanned single degree of freedom comparisons were used to evaluate linear and quadratic responses to P fertilizer rates for each crop year. These comparisons were calculated as described by Steel and Torrie (1980). The error mean square was used as the best estimate of pooled error to test significance of these preplanned comparisons. Significant F values were sought at P 0.05.

	Results and discussion

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
Responses to P fertilizer rates are combined across genotypes. Interactions of genotypes and P were discussed separately (unpublished data, 1999). The soil at Location 1 had a lower pH than the soils at the other three locations which had similar pH values (Table 2) . Also, Pw at Location 1 was substantially higher than at Locations 2, 3, and 4. The lower Pw values at Locations 2, 3, and 4 may be directly related to their higher pH values because the solubility of P in water decreases as pH increases. Location 1 had a lower Pa than locations 2, 3, and 4, but the magnitude of the difference was not as great as for Pw. Locations 2, 3, and 4 were similar in Pw, and Locations 3 and 4 had moderately lower Pa values than Location 2 (Table 2).

Korndörfer et al. (1995) classified the Pa of 17.9 kg ha^-1 at Location 1 (Table 2) at the low end of the medium group. For this Pa classification, they predicted that a positive yield response to moderate rates of P fertilizer would be likely. Since a positive yield response occurred from P0 to P2, Pa was more useful than Pw for predicting response to P fertilizer at Location 1.

The same genotypes were planted at Locations 1 and 2. A positive yield response to increasing rates of P fertilizer was expected at Location 2 based on the higher pH and the lower labile soil P (Pw) at Location 2 compared with Location 1 (Table 2). However, at Location 2 there were no significant responses to P fertilizer for TRS, TCH, and TSH (Table 4) . Of the four locations in this study, the soil at Location 2 had the highest Pa (Table 2) and was classified at the high range of the medium group described by Korndörfer et al. (1995). At this classification, a yield response was predicted by Korndörfer et al. (1995), but not with as much certainty as for lower Pa values. Thus, neither Pw nor Pa predicted the lack of response to P fertilizer at Location 2.

The soil at Location 3 was similar in pH and Pw to Location 2, however, its Pa was more similar to that of Location 1 (Table 2). The yield responses at Location 3 also were more similar to those of Location 1 than Location 2. From the plant-cane through the second-ratoon crops, TCH and TSH had positive linear responses to increasing rates of P fertilizer (Table 5) . However, quadratic models also described the responses well in all three crops. These quadratic responses were due to large increases from P0 to P1 and then moderate increases from P1 to P2. Both the Pw and Pa results predicted the positive TCH and TSH responses to increasing rates of P fertilizer at Location 3.

Glaz and Ulloa (1994) reported that more available P caused reductions in TRS on a soil similar in pH and Pw to that of Location 1 and higher in Pw than that of Location 3. Based on these previous results, we expected increasing P to cause decreases in TRS at Location 1 rather than at Location 3. Similarly, the Pa results did not explain the second-ratoon decrease in TRS. A possible explanation for these unexpected results is that the TRS response is genotype dependent, because a different group of eight genotypes was used at Locations 1 and 3.

Location 4 was similar in pH and Pw to Locations 2 and 3 and more similar in Pa to Location 3 than Location 2 (Table 2). Yield responses to P at Location 4 resembled those at Location 3 more than Location 2. The TRS at Location 4 declined linearly with increasing P rates in the plant-cane crop and showed a tendency to decline in the second-ratoon crop (Table 6) . Quadratic fits best described the plant-cane and second-ratoon responses of TCH and TSH at Location 4. In the plant-cane crop, the TCH declined from P1 to P2. This decline, along with the linear TRS decline, resulted in a TSH yield at P2 similar to that at P0. Second-ratoon TCH and TSH responses were similar to those of plant cane except that yields remained similar at P1 and P2. In the first-ratoon crop at Location 4, TRS did not respond to P while TCH and TSH had moderate linear increases with increasing P fertilizer. Both the Pw and Pa tests were effective at predicting TCH and TSH increases from P0 to P1. However, the moderate Pa result was more indicative that positive yield responses would not continue from P1 to P2. Neither Pw nor Pa was effective at predicting the negative TRS responses.

Choosing P fertilizer rates in the EAA is a difficult process. As with other farm operations, an important consideration is to choose the level of P fertilizer that will result in the greatest profit margin. In addition, P is naturally a limiting nutrient in the Everglades. Therefore, EAA farmers are being requested to reduce the P content of their drainage water to the greatest extent practical. These farmers already pay a tax of $62 ha^-1, which was based on previous P enrichment to the Everglades from the EAA. The possibility that new, more stringent P regulations will be adopted has persuaded EAA farmers to proactively seek more effective P reduction measures. One such measure would be to refine soil-test P calibrations.

Further adding to the complexity of the P issue for EAA farmers is that, as shown in this study, sugarcane yield responses to P are difficult to predict on the Histosols of the EAA. The yield correlations upon which P recommendations are based were reported in 1974 and 1979 (Gascho and Freeman, 1974; Gascho and Kidder, 1979). Diaz et al. (1993) explained that P mineralization rates in Histosols vary due to factors such as soil mineral content, cultivation, crop type, and moisture content. They estimated that under well-drained conditions, EAA Histosols mineralize 17 to 39 kg P ha^-1 yr^-1. Excepting crop type, all the factors that affect soil P mineralization have changed considerably since 1979, when the P calibrations now in use were reported. Also, the genotypes used now by EAA growers are separated by several generations from the genotypes used before 1979, so perhaps crop type also has changed.

The present study offered some clarification, but also raised several questions. We found that testing the soil for Pa as described by Korndörfer et al. (1995) provided a better basis for P-fertilizer recommendations than the Pw test on organic soils with low Pw values. However, previous findings relating pH and P were not confirmed in this study. Further, there were some important, but not well defined, differences in TCH and TSH responses due to crop year (i.e., plant cane, first ratoon, or second ratoon). TRS responded positively, not significantly, or negatively to increasing P rates, and neither Pw nor Pa were useful in predicting these responses. Crop year may have affected this response, although as with TCH and TSH, this effect was not well defined. As explained in more detail in another report (unpublished data, 1999), one possible explanation for the unexpected TRS responses to P may be that they are more genotype-dependent than TCH responses.

There are substantial gaps regarding the response of sugarcane to P in the EAA. Due to ecological concerns, a critical research program for sugarcane farmers is to have these knowledge gaps filled. Evidence in the present study suggests that more detailed studies of soil pH and sugarcane genotype and their interactions with soil P are logical subject areas for further research. As previously explained by Diaz et al. (1993), more knowledge about factors affecting P mineralization rates probably also would improve P soil test calibrations for sugarcane yields.SAS Institute 1985

Received for publication June 15, 1999.

	REFERENCES

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This Article Abstract Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Glaz, B. Articles by Ulloa, M. F. Search for Related Content PubMed Articles by Glaz, B. Articles by Ulloa, M. F. Agricola Articles by Glaz, B. Articles by Ulloa, M. F. Related Collections Other Crops Nutrient Management Soil Fertility and Productivity