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SUGARCANE

Sugarcane Genotype Response to Phosphorus Fertilizer in the Everglades

^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}saa.ars.usda.gov

	ABSTRACT

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Summary REFERENCES

 
To protect the natural Everglades, federal legislation mandates a reduction of at least 25% in the P content of water discharged from the Everglades Agricultural Area (EAA). Work is needed to achieve these reductions while sustaining a productive agriculture in the EAA. The objective of this study was to identify differences in response to P fertilizer among 24 elite genotypes of sugarcane (interspecific hybrids of Saccharum spp.). Six yield characteristics were examined on Histosols at four field locations with no added P, an often used commercial rate of 24 kg P ha^-1, and 48 kg P ha^-1 for the plant-cane, first-ratoon, and, in three locations, the second-ratoon crop. One group of eight genotypes was planted at two locations, and two other groups of eight genotypes each were planted at one of two other locations. Genotype x P fertilizer rate interactions were generally not significant. Of the eight genotypes tested at two locations, CL 61-620, CP 72-2086, and CP 85-1308 were cautiously (P 0.15) identified at both locations as more sensitive than other genotypes to changes in P rates. Reduced P rates were recommended for CP 85-1308 on soils with low P. CL 73-239 and CP 81-1254 required more than commonly recommended P fertilizer on low-P soils. Identification of sugarcane genotypes that respond favorably to varying rates of P may evolve into a cost-effective strategy to reduce P content of EAA drainage water.

Abbreviations: BMP, best management practice • EAA, Everglades Agricultural Area • P, phosphorus • P₂₄, 24 kg P ha^-1 • P₄₈, 48 kg P ha^-1 • Pa, acetic acid–extractable soil P • P_lin, linear regression on P rate • P_quad, quadratic regression on P rate • P_zero, no P fertilizer applied • Pw, water extractable, labile soil P • STAs, storm water treatment areas • TCH, metric tons cane ha^-1 • TRS, theoretical recoverable sugar • TSH, metric tons sugar ha^-1

	INTRODUCTION

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Summary REFERENCES

 
THE EVERGLADES AGRICULTURAL AREA (EAA) is a 280000-ha agricultural basin of Histosols in southern Florida. Sugarcane is grown on about 144000 ha in the EAA (Glaz, 1998). Legislation mandates a reduction by at least 25% in the P content of water discharged from the EAA by the year 2002. This reduction will be compared with a 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 will be converted from agriculture to specially designed artificial wetlands to serve as storm water treatment areas (STAs) (Stone and Legg, 1992). The P concentration of water released from these STAs must be no more than 50 µg L^-1 by the year 2002 (Walker, 1996). Walker (1996) further reported that 50 µg L^-1 is much higher than the natural background levels of <10 µg P L^-1 in the Everglades. Research has since documented changes in natural populations of Everglades flora and fauna at P concentrations >10 µg L^-1 (McCormick et al., 1999).

Farmers in the EAA are using an extensive best management practice (BMP) program to meet P-reduction requirements (Izuno and Capone, 1995). Stone and Legg (1992) estimated that BMP implementation cost farmers $153 ha^-1 and annual operation and maintenance costs were about $9 ha^-1. Two cost-effective BMPs would be productive sugarcane cultivars that either remove more P from a given soil or yield well at lower than currently recommended rates of P fertilizer. Glaz et al. (1997) reported on progress in developing the first of these two BMPs. They estimated that among 12 elite sugarcane genotypes, there was a range of 8.5 kg ha^-1 in P removed from the soil and there was substantial variability for this trait among the 12 genotypes. In addition, two genotypes that represented high and low extremes for leaf P content had high cane yields. Kumar and Verna (1997) also reported differences in leaf P content of 11 genotypes in India. However, contrary to Glaz et al. (1997), Kumar and Verna (1997) reported high correlations between leaf P and sugar and cane yields.

Previous studies have evaluated genotype response to P for other crops. Nagata et al. (1992) concluded that six crisphead lettuce (Latuca sativa L.) cultivars responded similarly to several rates of P in the EAA. James et al. (1995) found a significant cultivar x P fertilizer interaction for five alfalfa (Medicago sativa L.) cultivars and three P rates and concluded that P-use efficiency in alfalfa could be improved. Mugwira and Haque (1993) reported a differential response to P in plant height in Ethiopia among Sesbania accessions, and concluded that Sesbania could be screened for tolerance to low P.

Sugarcane is by far the major crop in the EAA. If its genetic variability for water tolerance and P response is similar to that demonstrated for other characteristics, then research could help farmers use sugarcane to achieve lower P discharges (Glaz, 1995). Several other crops are grown in the EAA that require much higher rates of P than sugarcane (Sanchez, 1990). A common practice is to rotate such crops with sugarcane. This practice helps contain and reduce the residual P of the previous crop because of the low P requirement and flood tolerance of sugarcane. Due to its low P requirement, supplemental P fertilizer is not needed for sugarcane in this rotation. The relatively high water tolerance of sugarcane allows farmers to drain water from sugarcane fields more slowly than from most other crops in the EAA. Thus, following storms, farmers often pump out, at lower rates, less total water from sugarcane fields than from other fields. Such pumping practices help reduce P discharge (Izuno and Capone, 1995).

A problem with growing sugarcane in a field after heavy fertilization with P is that t cane ha^-1 (TCH) may increase and theoretical recoverable sugar (TRS), measured as kg sucrose t^-1 of cane, may decrease due to high residual soil P (Glaz and Ulloa, 1994). Even though t sugar ha^-1 (TSH) may stay the same or increase moderately in these rotations, profits may decline due to the increased expenses associated with handling and processing the extra cane tonnage (Deren et al., 1995). Thus, identification of genotypes that yield well in soils with high P levels would be useful in maintaining the desirability of growing sugarcane after crops that require high P fertilizer rates.

The objective of this study was to identify differences in response to P fertilizer among 24 elite sugarcane genotypes. Genotypes that yield well with less than recommended rates of P would serve directly as BMPs to reduce P in discharge water. Contrarily, sugarcane genotypes that yield well with more than recommended soil P would help farmers maintain crop diversity and still contain P discharge.

	Materials and methods

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Summary 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 each were tested at one of two other field locations. All four locations were in Palm Beach County, Florida. 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 southernmost area where sugarcane is produced in Palm Beach County.

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

At Locations 1 to 3, soil samples were collected soon after planting from two of the eight plots in each replication that were not fertilized with P. At Location 4, soil samples were collected before planting from the 24-ha field in which the experiment was conducted. The samples were analyzed for pH (Sanchez, 1990), water-extractable P (Pw) (Sanchez, 1990), and acetic acid–extractable P (Pa) in the Soil Testing Laboratory of the University of Florida/Institute of Food and Agricultural Sciences, Everglades Research and Education Center, Belle Glade. The Pw procedure measures labile P and the Pa procedure measures labile and reserve P.

All plots were fertilized with Cu, Mn, Zn, and B at commonly used commercial rates in the EAA (Sanchez, 1990) and with K at the rate of 186 kg ha^-1. The planting dates of the experiments were December 1993 (Location 1), 23 Nov. 1993 (Location 2), 29 Dec. 1994 (Location 3), and 22 Nov. 1995 (Location 4). Plots were four rows, 10.7 m long, with 1.5 m between rows. The experiments at Locations 1, 3, and 4 were conducted for 3 crop years, the plant-cane, first-ratoon, and second-ratoon crops. The experiment at Location 2 was conducted for 2 crop years, the plant-cane and first-ratoon crops.

Randomized complete-block designs with four replications were used for all experiments. Each experiment had two factors, P fertilizer rates and sugarcane genotypes. Fertilizer rates were: no P fertilizer (P_zero); 24 kg P ha^-1 (P₂₄); and 48 kg P ha^-1 (P₄₈). These fertilizer treatments were applied in each crop year of each experiment. Fertilizer-application dates for all experiments are shown in Table 1 . These dates coincided with the dates fertilizers were applied in the commercial field in which experiments were planted.

The yield characteristic on which sugarcane is primarily judged is TSH. The two major components of TSH are TRS and TCH. The product of TRS and TCH divided by 1000 equals TSH. To measure TRS, 10-stalk samples were collected from all plots. Dates these samples were collected are listed in Table 1. To choose stalks for each sample, a starting point was selected randomly from one of the two middle rows of each plot, and from that starting point, the next 10 mature stalks were collected. Usually between one and three stools of sugarcane were needed to obtain the 10 stalks. Since sugarcane grows in large stools of primary, secondary, tertiary, etc. stalks, this sampling procedure helps collect a representative mixture of stalks.

Theoretical recoverable sugar was calculated from the Brix and polarimeter reading of each sample using a previously described procedure (Legendre, 1992). As described by Meade (1963), 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 juice temperature. The polarimeter reading, as described by Meade (1963), is a value without units obtained from polarization of the sugar solution in a saccharimeter. Stalk number ha^-1 was multiplied by stalk weight to calculate TCH. Stalk weight was measured from the same sample of 10 stalks that was used to calculate TRS. Dates when stalk counts were conducted are shown in Table 1.

Analyses of variance were calculated with MSTATC (Freed et al., 1991) using a randomized complete-block design for genotypes and P rates with crop years as a split plot on genotypes and P rates. Genotypes, P rates, and crop years were classified as fixed effects. The main-plot error mean square was used as the best estimate of pooled error to test significance of linear and quadratic responses to P rates and all interactions involving genotype and P rates. The error mean square was used as the best estimate of pooled error to test significance of genotype x P rate x crop year interactions. The experiment at Location 1 was conducted for 3 yr and the experiment at Location 2 was conducted for 2 yr. Therefore, even though the same group of genotypes was tested at these two locations, each location was analyzed separately.

Sixteen preplanned single degree of freedom comparisons were used to identify differences in genotype responses to P fertilizer rates at each location for each response variable. We tested the interaction of each genotype mean vs. the mean of the other seven genotypes in the same experiment x the linear (P_lin) and quadratic (P_quad) regressions on P rate. For example, to examine responses of CL 72-321 at Location 1, F values for two single degree of freedom comparisons were calculated for each response variable as described by Steel and Torrie (1980). One comparison was CL 72-321 vs. the mean of the other seven genotypes tested at Location 1 x the linear response to P (CL 72-321 vs. mean of others x P_lin). The second comparison was CL 72-321 vs. the mean of the other seven genotypes x the quadratic response to P (CL 72-321 vs. mean of others x P_quad). Significant F values were sought at P 0.10. When comparisons at P > 0.10 are discussed, the actual probabilities are provided.

	Results and discussion

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Summary REFERENCES

 
Soil pH, Pw, and Pa values at each location are shown in Table 2 . The relationships between these soil measurements and yields are reviewed by Glaz et al. (2000). Commercial P fertilizer rates of 24 kg ha^-1 were determined according to Pw values for Locations 2 to 4 (Sanchez, 1990). The grower at Location 1 used the lower Pa value and the somewhat higher Pw value to also decide on a commercial P fertilizer rate of 24 kg ha^-1. Since this study was initiated, more growers have begun using Pa rather than Pw, or combining their use as was done at Location 1. Thus, both Pw and Pa results are included in Table 2.

Locations 2 to 4 had particularly low Pw values and the Pw at Location 1 was low when compared with the population of EAA soils. Additionally, the Pa at Location 1 was the lowest among the four locations in this study. These four locations were carefully chosen based on these low soil P values. Due to this selection of locations, our results pertain only to similar soils. However, one of our interests was to identify genotypes that needed less than recommended rates of P fertilizer. If such genotypes yield well with less than the recommended P rate on organic soils in the EAA with low P, they may also yield well with less than the recommended P rate on organic soils with higher P; however, this is conjecture. We were also interested in identifying genotypes that yield well when following crop species for which high amounts of P fertilizer were applied. To approximate this response, we chose the rate of 48 kg P ha^-1. This was double the P rate applied commercially at each location. However, available soil P may be higher for sugarcane following some crops than for conditions encountered in our P₄₈ plots.

Location 1 ("20-Mile Bend Farm" of Sugar Farm Cooperative, Eastern Division)
The overall genotype x P interactions were not significant for all characters except TRS (Table 3) . The preplanned single degree of freedom comparisons identified two genotypes, CP 81-1254 and CP 85-1308, that responded to P rates differently than the mean of the other seven genotypes for some of the six dependent variables.

Location 2 (First Experiment Planted at Okeelanta Corp.)
There were no significant F values for overall genotype x P interactions at Location 2 (Table 5) . Four of the eight genotypes—CL 61-620, CP 85-1308, CP 73-1547, and CP 72-2086—had significant preplanned single degree of freedom comparisons for some characteristics. Genotype CP 85-1308 also had significant preplanned single df comparisons at Location 1. Additionally, two of the other three genotypes—CL 61-620 and CP 72-2086—had nearly significant preplanned comparisons at Location 1. For CL 61-620, these preplanned comparisons were for Brix and stalk weight and for CP 72-2086, the comparisons were for Brix and stalk number (Table 3).

The mean Brix of the other seven genotypes declined moderately with increasing P levels compared with the moderate increase in Brix of CP 73-1547 (Tables 5 and 6). However, this did not translate into a significant single df genotype x P interaction for TRS. Thus, there are no immediate commercial uses for this mild sensitivity of CP 73-1547 to P. However, this response identified CP 73-1547 as a genotype that may be useful for developing genotypes that yield well at higher than recommended rates of P fertilizer.

The quadratic response of CP 72-2086 for stalk weight differed from that of the mean of the other seven genotypes (Table 5). However, the TCH response of CP 72-2086 was similar to that of the mean of the other seven genotypes (Tables 5 and 6). Like CL 61-620, CP 72-2086 had several nearly significant interactions at Locations 1 and 2. The quadratic Brix reactions of CP 72-2086 differed from those of the other seven genotypes at at both Locations 1 and 2 (Tables 3 and 5). Similarly, the preplanned comparison for CP 72-2086 for stalk number was significant at at Location 1 (Table 3). Due to these elevated probability levels, CP 72-2086 should be cautiously categorized as a genotype that responded to P rates differently than other genotypes at Locations 1 and 2. Due to its substantial commercial use in Florida (Glaz, 1998), CP 72-2086 is a likely candidate for further testing aimed at better identifying its response to P rates.

Location 3 (Second Experiment Planted at Okeelanta Corp.)
The F values for overall genotype x P interactions were significant for stalk weight and highly significant for stalk number, TCH, and TSH at Location 3 (Table 7) . Genotypes CL 73-239, CP 85-1432, CP 85-1491, CP 78-1628, and CP 80-1743 had significant preplanned single degree of freedom comparisons (Table 7).

Genotype CP 85-1491 had higher stalk weight, stalk number, TCH, and TSH at P_zero than the mean of the other genotypes (Tables 7 and 8). Also, these characters showed less of a positive response to increasing P for CP 85-1491 than for the mean of the other genotypes (Tables 7 and 8). Although this identified CP 85-1491 as a genotype that may require less P fertilizer than others, the classification was not as desirable as for CP 85-1308 at Location 2 where CP 85-1308 did not have yield losses associated with decreased P fertilizer (Table 6). With CP 85-1491, there were losses with decreased P, but the losses were not as severe as for the means of the other genotypes. These responses identified CP 85-1491 as a desirable parent in a program designed to develop genotypes that yield well at low P rates.

The quadratic responses of CP 78-1628 for TRS and stalk weight as well as the linear response for stalk number differed from those for the means of the other genotypes (Table 7). The TRS of CP 78-1628 declined from P_zero to P₂₄ but increased to its maximum from P₂₄ to P₄₈ (Tables 7 and 8). The TRS of the mean of the other genotypes was similar across the three P rates (Table 8). Since the stalk weight and stalk number responses of CP 78-1628 from P₂₄ to P₄₈ canceled their effects on TCH, the TRS response of CP 78-1628 identified it as a genotype that yielded well at both lower and higher than recommended P rates.

The linear responses to increasing P rates of CP 80-1743 for stalk number and TCH differed from those of the other genotypes (Table 7). The mean stalk number and TCH of the other genotypes increased quadratically as P increased, but for CP 80-1743 these traits increased from P_zero to P₂₄ and then decreased from P₂₄ to P₄₈ (Tables 7 and 8). Thus, CP 80-1743 had its highest yields at P₂₄, the recommended P fertilizer rate. Further testing of CP 80-1743 between P_zero and P₂₄ is warranted to determine if maximum yields would be reached at rates less than P₂₄. Based on its loss of yield at P₄₈, CP 80-1743 would not be recommended for planting after crop species that require high rates of P fertilizer.

Location 4 (Third Experiment Planted at Okeelanta Corp.)
The F values at Location 4 for overall genotype x P interactions for all characteristics except stalk number were <1, and the F value for stalk number was significant (Table 9) . Of the eight genotypes at Location 4, only CP 90-1428 had significant preplanned single degree of freedom comparisons (Table 9). Like CP 80-1743 at Location 3, these interactions for stalk number identified CP 90-1428 as a genotype that yielded well at recommended rates of P and should not be used where P rates are high (Table 8). However, based on its lack of TRS, TCH, and TSH increases from P₂₄ to P₄₈, CP 90-1428 should be tested at additional P rates between P_zero and P ₂₄ to determine if its yields would peak before P₂₄.

	Summary

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Summary REFERENCES

 
Twenty-four genotypes were tested at three P fertilizer rates. Genotypes CL 61-620, CL 73-239, CP 78-1628, and CP 81-1254 were the most promising genotypes identified for use when sugarcane follows a crop that requires high P fertilizer rates. Genotypes CL 73-239 and CP 81-1254 were further identified as particularly poor choices for reducing P content of discharge water from soils with low P. Conversely, CP 85-1308 (based on results at one of two locations), CP 80-1743, and CP 90-1428 should not be used with higher than recommended rates of P.

Genotypes CP 85-1308 and CP 78-1628 had high yields relative to the other genotypes with no added P fertilizer. A reduced rate of P for CP 85-1308 can be immediately recommended for soils with low Pw and moderate Pa values. Genotype CP 72-2086 should be tested further since it is a widely used cultivar and data suggested that its reactions to changes in P rates were sometimes different from the reactions of other genotypes. Candidates identified for follow-up testing with P fertilizer rates between 0 and 24 kg ha^-1 were CP 80-1743, CP 85-1308, CP 85-1491, CP 88-1762, CP 90-1113, CP 90-1428, CP 90-1435, CP 90-1464, and CP 90-1549. Genotype CP 73-1547 may be useful for developing genotypes that yield well under high P conditions. Conversely, CP 85-1491 may be useful for developing genotypes that yield well at less than recommended P rates.

Variance ratios for single df comparisons testing genotype x P rate interactions were not significant for most traits of most genotypes. One group of eight genotypes was tested at two locations. Not one of these eight genotypes had significant F values for the same preplanned comparison at both locations. However, sufficient variability for response to P rates was identified in this study to suggest that breeding programs could improve desired characteristics. The purpose of such a breeding program would be to seek genotypes that yield well under certain P conditions to become one of several BMPs in a long-term effort to reduce P in EAA drainage water. The strategy could yield positive consequences similar to those expected from reducing P fertilizer by adhering to fertilizer recommendations from calibrated soil tests.

	ACKNOWLEDGMENTS

 
The authors acknowledge that several helpful comments originated from the anonymous review process.

Received for publication July 13, 1999.

	REFERENCES

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Summary REFERENCES

 

• Deren C.W., Alvarez J., Glaz B. Use of economic criteria for selecting clones in a sugarcane breeding program. Proc. Int. Soc. Sugar Cane Technol. 1995;21:437-447.
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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 Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Web of Science (3) 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 Water Quality Wetlands and Aquatic Processes Sustainable Agriculture Other Crops Nutrient Management Crop Genetics