Journal of American Society of Sugar Cane Technologists, Vol. 37, 2017

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1 Journal of American Society of Sugar Cane Technologists, Vol. 37, 2017 SUGARCANE YIELDS DO NOT RESPOND TO PHOSPHORUS FERTILIZER IN RATOON CROPS OF LCP IN LOUISIANA Richard M. Johnson 1*, Howard P. Viator 2, Jay C. Stevens 3, and Brenda S. Tubaña 4. 1 USDA/ARS, Sugarcane Research Unit, 5883 USDA Rd., Houma, LA 70360, 2 Sugar Research Station, Louisiana State University AgCenter, 5755 LSU Ag Road, St. Gabriel, LA Dean Lee Research and Extension Center, Louisiana State University Agricultural Center, 8105 Tom Bowman Drive, Alexandria, LA School of Plant, Environmental and Soil Sciences, Louisiana State University Agricultural Center, Baton Rouge, LA * Corresponding author: address: (richard.johnson@ars.usda.gov) ABSTRACT The effects of phosphorus fertilizer on sugarcane (interspecific hybrids of Saccharum Spp. cv. 'LCP ') yield components and soil properties were evaluated at seven locations in Louisiana. Five rates of phosphorus fertilizer (0-84 kg P2O5 ha -1 ) were applied to first-, secondand third-ratoon commercial sugarcane fields in Louisiana. Soil samples were collected prior to fertilizer application and after harvest and sugarcane leaf samples were collected during the grand growth stage. All experimental plots were harvested with a single row, chopper harvester and a field transport wagon equipped with electronic load sensors to determine cane and sugar yields. Sugarcane juice quality was determined from a random cane sample in each plot. Our results demonstrated that phosphorus fertilizer did not show a consistent positive influence on cane or sugar yields. Soil properties data showed that significant increases in soil phosphorus levels did occur in the surface layer (0-15 cm) with P levels increasing from 14 to 28 mg kg -1. No increases were observed deeper within the soil profile (15-30 cm). Small increases in plant phosphorus were observed, but were only significant for one rate (average over locations). These combined data suggest that there is no justification for the application of phosphorus fertilizer to LCP in Louisiana. Although, it is possible that different results would be obtained if higher levels of soil phosphorus were applied, it is more likely that LCP does not respond to phosphorus fertilizer, an observation reported from many Louisiana sugarcane growers. Additional research should be conducted to evaluate the phosphorus response of newly released varieties, as they may respond more favorably to phosphorus fertilizer. Keywords: phosphorus, fertilizer recommendations, ratoon crops, sugarcane yields. INTRODUCTION The process of identifying limiting soil and nutrient components for sugarcane is complicated by several factors. The perennial nature of the crop and the extended fallow period between crop cycles lead to soil and nutrient effects that carry-over between crop years and even between successive crop cycles. Nutrient requirements and accumulation also differ between newly planted cane and successive ratoon crops (Wood et al., 1996), with older ratoons generally requiring higher nutrient amounts. In most of the sugarcane producing areas of the world, nitrogen has been identified as the predominant soil nutrient in sugarcane in terms of its contribution to crop productivity (Meyer and Wood, 2001). Nitrogen fertilizer can increase 1

2 Johnson et al.: Sugar yields do not respond to phosphorus fertilizers in ratoon crops sugarcane gross cane yield at the expense of sucrose concentration (Muchow et al., 1996; Wood, 1990). It is, therefore, necessary to balance nitrogen applications such that optimum cane and sucrose yields are obtained. The next most important soil nutrients in sugarcane production are potassium and phosphorus. Phosphorus and potassium were found to increase cane yields in a study in South Africa, while having a minimal effect on sucrose concentrations (Wood, 1990). In contrast, El-Tilib et al. (2004) found significant increases in both cane and sucrose levels with applied potassium and phosphorus in a study in Sudan. Salazar and Sanchez (2010) reported that sugarcane response to potassium and phosphorus in Ecuador was location specific, but in a majority of locations applications of 30 to 60 kg ha -1 P2O5 increased cane and sugar yields. Application of 100 kg ha -1 K2O increased cane and sugar yields in two of three locations, while at the third location, only theoretically recoverable sucrose (TRS) was observed to increase. The nitrogen nutrition of sugarcane in Louisiana has been extensively studied and recently nitrogen rates were reduced based on new research results with current varieties and fertilizer sources (Johnson et al., 2008). In contrast, rates for potassium and phosphorus have remained unchanged for decades and are based, in part, on fertilizer calibration studies that were conducted with varieties that are no longer produced in the industry (Ricaud, 1965; Golden and Ricaud, 1963; Golden, 1968). Overall, there is a lack of published research results for both phosphorus and potassium fertilizer response in Louisiana. The authors of one of the few recent potassium studies in Louisiana that utilized newer varieties (Wang et al., 2007, 2008) reported significant increases in both cane and sugar yields in plant-, first-, and second-ratoon cane crops. In a majority of cases significant increases in sugar yield were obtained with 67 kg K2O ha -1, although in one study 268 kg K2O ha -1 was required to achieve a significant response, a clearly uneconomic amount. No recent work has been published on phosphorus requirements in Louisiana. In addition, several informal reports from producers reported that LCP , a major Louisiana variety in 2004, was not responsive to fertilizer phosphorus. Due to this observation, many producers had eliminated phosphorus from their fertility programs. The specific objective of this experiment was investigate this observation and to determine the cane and sugar yield response of ratoon LCP sugarcane in Louisiana to supplemental phosphorus fertilizer. MATERIALS AND METHODS Soil classification of experimental fields Phosphorus fertilizer experiments were conducted in first-, second-, and third-ratoon commercial sugarcane fields of cv. LCP (Milligan et al., 1994) at seven locations throughout the Louisiana sugarcane industry. Three trials were conducted in 2005 and four in The first 2005 experimental location was a third-ratoon field at Cedar Grove Plantation in Labadieville, LA. The soils at this site were mapped as Cancienne silt loam and silty clay loams (fine-silty, mixed, superactive, nonacid, hyperthermic Fluvaquentic Epiaquepts). The second 2005 site was at third-ratoon field at Patout Brothers Farms in Jeanerette, LA. The soil at this site was mapped as a Jeanerette silt loam (fine-silty, mixed, superactive, thermic Typic Argiaquolls). And the third 2005 site was a first-ratoon field at Triple V Farms in Youngsville, LA. The soil at this site was mapped as a mix of Frost silt loams (fine-silty, mixed, active, thermic Typic Glossaqualfs) and Coteau silt loams (fine-silty, mixed, active, hyperthermic Glossaquic Hapludalfs). 2

3 Journal of American Society of Sugar Cane Technologists, Vol. 37, 2017 The first 2007 location was a second-ratoon field at Triple V Farms that was approximately1.2 km from the 2005 site. The soils at this site were also mapped as a mix of Frost silt loams (fine-silty, mixed, active, thermic Typic Glossaqualfs) and Coteau silt loams (fine-silty, mixed, active, hyperthermic Glossaquic Hapludalfs). The second 2007 site was a second-ratoon field at Mount Lawrence Plantation in Labadieville, LA. The soil at this site was mapped as Cancienne silt loam (fine-silty, mixed, superactive, nonacid, hyperthermic Fluvaquentic Epiaquepts). The third 2007 site was a first-ratoon field at Gerald Thibodeaux & Sons Farms in Paincourtville, LA. The soil at this site was mapped as a Schriever clay (veryfine, smectitic, hyperthermic Chromic Epiaquerts). The fourth 2007 site was a first-ratoon field at Keith Dugas Farms in Paincourtville, LA. The soil at this site was mapped as a Cancienne silt loam (fine-silty, mixed, superactive, nonacid, hyperthermic Fluvaquentic Epiaquepts). Phosphorus treatments Phosphorus fertilizer was applied at rates of 0, 34, 50, 67, 84 kg P2O5 ha -1 on each side of the planted row using super-triple phosphate as the phosphorus source. Phosphorus treatments were surface broadcast in mid-april (early tillering phase), and plot size was 3 rows (inter-row spacing was 1.8 m) by 15-m in length. Treatments were arranged in a randomized complete block design with six replications. Quantities of nitrogen and potassium were maintained by cooperators as recommended for first-, second-, and third-ratoon crops on silt-loam (light textured) and clay (heavy textured) soils. The LSU AgCenter currently recommended nitrogen levels range from 90 to 134 kg N ha -1 and potassium levels from 90 to 157 kg K2O ha -1. Soil and plant sampling and analysis Soil samples (0-15 cm) were collected from all plots prior to fertilizer application and after harvest (0-15, cm) to determine soil nutrient levels. At the Mount Lawrence location in 2007 it was not possible to collect the post-harvest soil samples, because the grower tilled the field before it could be sampled. Soil samples were air-dried, ground with an electric grinding mill (Straub 4E, QCG Systems, Phoenixville, PA) and shipped to A&L Laboratories (Memphis, TN) for analysis. Soil properties determined included organic matter content (OM), ph, buffer ph, exchangeable cations (Ca, Mg, K), cation exchange capacity (CEC), phosphorus, and sulfur. Phosphorus and major cations present in soil samples were estimated using the Mehlich III extraction procedure and Inductively Coupled Plasma-Atomic Emission Spectrophotometry (EPA Method 200.7). Soil OM was determined by loss on ignition (Nelson and Sommers, 1996). Soil ph was determined in a 1:1 (m/v) soil to water suspension and soil buffer ph using the SMP buffer (Thomas, 1996). The soil CEC is calculated by summing exchangeable cations. Soil fertility levels were based on the A&L Laboratory recommendations for sugarcane grown in Louisiana. Stalk heights (12/plot, meters) and stalk number (plot total) were determined during the grand growth period. Only stalks that were at least 1.2-m tall when measured from the soil surface to the youngest visible leaf collar were counted and measured. Leaf samples (youngest fully expanded leaf) for tissue analysis were also collected during the grand growth period, ovendried, ground and analyzed by nitric acid-hydrogen peroxide digestion and ICP spectroscopy to serve as an indicator of fertilizer-use efficiency. 3

4 Johnson et al.: Sugar yields do not respond to phosphorus fertilizers in ratoon crops Yield determination Experimental plots were harvested with a single-row, chopper harvester (John Deere, Thibodaux, LA, USA) and cane weight in each plot was determined using a modified single-axle high-dump billet wagon (John Deere, Thibodaux, LA) equipped with load sensors mounted on the spindles at the end of the axle and on the wagon s tongue where it connects to the tractor (Johnson and Richard, 2005). A billet sampler mounted on the weigh wagon was used to capture a random subsample of billets from each plot as it was being transferred from the harvester to the wagon. The sub-samples of the billeted cane were analyzed using the prebreaker, core press method (Legendre, 1992). Extracted juice was analyzed for Brix (% soluble solids content in cane, w/w) and sucrose (% in cane) and the bagasse was dried to determine fiber content (% in cane). Theoretical recoverable sugar (TRS, kg Mg -1 ) was calculated from the brix, sucrose and fiber data (Legendre, 1992) and cane (Mg ha -1 ) and sucrose (kg ha -1 ) yields were calculated using plot weights and TRS. Statistical analyses Data from phosphorus experiments were analyzed using the PROC MIXED procedure in SAS (SAS Institute, 2010). In our analyses, the seven sites represent random environmental conditions, such as different physical locations, different years and different ratoons. In the model used, fertilizer was considered as fixed, whereas, environment, replication within environment and environment x fertilizer were considered as random effects. Differences between treatment least square means were compared using the PDIFF option (Saxton, 1998) at the 0.05 probability level. RESULTS Soil properties from experimental locations The preliminary soil properties from the seven study sites did not exhibit any conditions that would have limited or reduced phosphorus availability or response, with possibly one or two exceptions (Table 1). The soil ph at all seven locations was within a range that would not have limited phosphorus availability with the lowest soil ph obtained at Triple V2 Farms (5.8) and the highest at Keith Dugas Farms (7.7) (Table 1). The preliminary soil phosphorus levels tested as "low" (5-14 mg kg -1 ) by the Mehlich III procedure and A&L Laboratories classification at five out of the seven locations, medium (15-30 mg kg -1 ) at one location (Mount Lawrence) and optimum (31-50 mg kg -1 ) at one location (GT Farms). It is possible that the two higher phosphorus test levels, particularly at GT Farms, may have obscured the phosphorus response at these locations. Preliminary screening of soil sample histories provided by cooperating growers (before initial sampling) did not suggest that the levels at these sites were in these ranges. All of the sites tested "medium" or above for potassium, with the exception of KD Farms which tested a "high-low". Calcium and magnesium tested as "medium" or above at all locations and sulfur tested "low" at five locations and "medium" at 2 locations. The organic matter levels were typical for Louisiana sugarcane soils ranging from 0.69 to 1.8% (Table 1). Phosphorus fertilizer effects on yield components There was not a significant response (P > 0.05) of cane yield, TRS, sugar yield, stalk heights or stalk population to phosphorus fertilizer rate (Table 2). As stated in the methods section, the analysis for all factors was combined across locations with the phosphorus rate by 4

5 Journal of American Society of Sugar Cane Technologists, Vol. 37, 2017 location interaction treated as a component of error and used for the overall mean comparisons. Cane yield did not respond consistently to applied phosphorus fertilizer (Table 3), with the plots receiving no phosphorus producing equal or greater yields than higher rates of applied phosphorus. TRS also did not show a consistent response to phosphorus fertilizer, with the plots receiving no phosphorus exhibiting a TRS that was statistically equivalent to all of the applied rates (Table 3). Although three of the four phosphorus rates produced sugar yields that were numerically greater than the control, they were not statistically significant (P > 0.05) (Table 3). A similar response was observed for both stalk heights and stalk population with no effect of phosphorus rate noted for either yield component (Table 3). Phosphorus fertilizer effects on soil and plant phosphorus levels There was a significant difference (P < 0.05) between initial soil phosphorus levels and phosphorus rate (Table 2). Although treatments were randomly assigned to plots within the experiment, a significant difference was detected between the plots receiving no phosphorus and those for the highest treatment rate (84 kg ha -1 ) in the analysis of the pretreatment soil samples (Table 4). These differences were detected prior to fertilizer application and resulted solely from chance. It should be noted that the magnitude of the difference in soil phosphorus between the two treatments was less than 2 mg kg -1, which should not adversely affect results. There was a significant effect (P < 0.05) of soil phosphorus rate on the final (after harvest) shallow (0-15 cm) soil phosphorus levels (Table 2). A significant increase in soil phosphorus levels was noted between the plots receiving no phosphorus and the two highest phosphorus rates (Table 4). In contrast, phosphorus application did not affect the final deep (15-30 cm) soil phosphorus levels (Table 2). There were not differences in deep soil phosphorus levels in response to rate, although a trend was noted showing an increase between the plots receiving no phosphorus and highest rate (Table 4). Phosphorus rate also did not show a significant interaction with plant phosphorus levels, (Table 2). A trend in the plant phosphorus data showed an increase in P content with increasing P rate (Table 4), the increase was significant at the 67 kg ha -1 rates. DISCUSSION The combined data from the seven phosphorus trials did not show any advantage to applying phosphorus fertilizer for cane yield, TRS, sugar yield, stalk height or population. Cane yields, TRS, and sugar yields were representative for ratoon crops of LCP grown in the Louisiana sugarcane production areas (Johnson and Richard, 2005) and did not appear to be depressed due to nutrient stress. Although, the majority of the test sites tested "low" for soil phosphorus, one site did test medium and one site optimum. The statistical analysis showed that the effects of location on the measured yield components were small compared to the effects of phosphorus rate, thus justifying combining over locations (data not shown). The soil ph at all locations was also in a range that should not have limited phosphorus availability (Gravois, 2014) and no other soil nutrients (possible exception sulfur) were limiting based on soil test levels. Phosphorus fertilizer was applied in these trials at rates up to 84 kg ha -1, which exceeds the currently recommended LSU AgCenter rates (Gravois, 2014) that vary from 0 to 67 kg ha -1. The soil phosphorus test levels in the shallow (0-15 cm) soil layer after harvest were increased significantly at the two highest rates. Soil phosphorus levels in the deep soil layer did not 5

6 Johnson et al.: Sugar yields do not respond to phosphorus fertilizers in ratoon crops increase, which suggest that vertical movement of phosphorus in the soil profile did not occur. Finally, plant phosphorus did show some small, but significant, increases in plant phosphorus with increasing phosphorus rate. These combined factors would suggest that the experimental conditions were ideal to expect a yield response to phosphorus fertilizer, and yet this did not occur. Several explanations for this lack of response are possible. If data are examined from the individual locations several possibilities exist. It is possible that, at some locations, all of the applied phosphorus was used by the plants within the growing season, but this did not translate into yield increases because insufficient quantities of phosphorus were available. This is most clearly suggested at Triple V Farms in 2007, where no increases in shallow soil phosphorus were detected. This is also possible at Cedar Grove Plantation, Patout Farms and Keith Dugas Farms, where minimal increases in shallow soil phosphorus were observed. However, at two of the locations, Mount Lawrence and GT Farms, soil phosphorus test levels were at medium and optimum, respectively and yield increases were still not observed. Also, at three of the four locations a numeric increase in plant phosphorus was noted, indicating phosphorus uptake was enhanced with phosphorus fertilization. However, at all locations the plant phosphorus levels were at or below the published critical value for plant phosphorus in Florida which is 0.19% (Anderson and Bowen, 1990). This would suggest that additional phosphorus may have been required to achieve significant increases in yield. However, it is also possible that the critical levels for phosphorus in the Louisiana sugarcane production area, which consists of mineral soils, differ from those in Florida, which consists largely of organic soils. Additional research would be required to further evaluate these effects. Another possibility is that the variety LCP is not responsive to phosphorus fertilizer. This possibility is, in fact, one of the driving forces behind this research project. Several informal reports from producers were received indicating that LCP , which was planted on up to 91% of the acreage in Louisiana in 2004 (Legendre and Gravois, 2005), was not responsive to fertilizer phosphorus. Many producers had eliminated phosphorus from their fertility programs based on these observations. Our research results would suggest that this may be a valid assumption. Therefore, future studies on sugarcane response to phosphorus should focus on newly released cultivars in the region. CONCLUSIONS The effects of phosphorus fertilizer on sugar yield and its components and soil properties were evaluated with LCP at seven locations in Louisiana. Our results demonstrated that phosphorus fertilizer did not increase cane and sugar yields in the soils and locations evaluated. Soil properties data showed that significant increases in soil phosphorus levels did occur in the surface layer (0-15 cm), but not deep within the soil profile (15-30 cm). Small increases in plant phosphorus were observed but were only significant for one rate. These combined data suggest that, there is no justification to apply phosphorus fertilizer to LCP in Louisiana. Although, it is possible that different results would be obtained if higher levels of soil phosphorus were applied, it is more likely that LCP does not respond to fertilizer phosphorus. Additional research should be conducted to evaluate the phosphorus response of new varieties as they are released to the Louisiana sugarcane industry. Soil and plant testing 6

7 Journal of American Society of Sugar Cane Technologists, Vol. 37, 2017 levels should also be revaluated to verify that the current recommendations are providing accurate estimates of sugarcane phosphorus requirements. ACKNOWLEDGEMENTS Mention of a trademark, proprietary product or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products or vendors that may also be suitable. We thank David Jones, Brenda King, Dean Ockmond, Michael Broussard, Jeremy Naquin, and Halley Burleson for assistance in soil and plant sampling. REFERENCES Anderson, D. L. and J. E. Bowen Sugarcane nutrition. Potash & Phosphate Institute, Atlanta, GA. El-Tilib, M.A., M.H. Elnasikh, and E.A. Elamin Phosphorus and potassium fertilization effects on growth attributes and yield of two sugarcane varieties grown on three soil series. J. Plant Nutr. 27: Golden, L.E. and R. Ricaud The nitrogen, phosphorus and potassium contents of sugar cane in Louisiana. Bull. La Agric. Exp. Stn. 574, 20 pp. Golden, L.E The relationship of sugar cane yields to the phosphorus and sulphur contents of certain Louisiana soils. Bull. La Agric. Exp. Stn. 633, 20 pp. Gravois, K Sugarcane Production Handbook Publ. 2859, Louisiana Agric. Exper. Station, Baton Rouge, LA. Johnson, R.M. and E.P. Richard, Jr Variability in sugar yield, sugar quality and soil properties in Louisiana sugarcane production systems. Agron. J. 97: Johnson, R.M., H.P. Viator, and B.L. Legendre Sugarcane fertilizer recommendations for the 2008 crop year. Sugar Bull. 86: Legendre, B.L The core/press method of predicting the sugar yield from cane for use in payment. Sugar J. 54 (9): 2-7. Legendre, B. L. and K.A. Gravois The 2004 Louisiana sugarcane variety survey. Pages in: Sugarcane Research Annual Progress Report. Louisiana Agric. Exp. Stn., Baton Rouge. Meyer, J.H. and R.A. Wood The effects of soil fertility and nutrition on sugarcane quality: a review. Proc. S. Afr. Sugar Technol. Assoc. 75:

8 Johnson et al.: Sugar yields do not respond to phosphorus fertilizers in ratoon crops Milligan, S.B., F.A. Martin, K.P. Bischoff, J.P. Quebedeaux, E.O. Dufrene, K.L. Quebedeaux, J.W. Hoy, T.E. Reagan, B.L. Legendre, and J.D. Miller Registration of LCP sugarcane. Crop Sci. 34: Muchow, R.C., M.J. Robertson, A.W. Wood, and B.A. Keating Effect of nitrogen on the time-course of sucrose accumulation in sugarcane. Field Crops Res. 47: Nelson, D.W. and L.E. Sommers Total carbon, organic carbon and organic matter. In: Methods of Soil Analysis. Part 3, Chemical Methods. SSSA No. 5, ASA, Madison, WI. Ricaud, R Soil potassium and response of sugar cane to fertilizer potassium in Louisiana. Bull. La Agric. Exp. Stn., 594, 36 pp. Salazar, M.E. and M.A. Sanchez Cane and sugar production of the variety ecu-01 with N, P, K, S and micronutrient application in plant cane. Proc. Int. Soc. Sugar Cane Technol. 27:1-7. SAS Institute Inc SAS Online Doc 9.2. SAS Institute Inc., Cary, NC. Saxton, A.M A macro for converting mean separation output to letter groupings in Proc Mixed. In: Proceedings 23rd SAS Users Group International, SAS Institute, Cary, NC, USA. pp Thomas, G Soil ph and Soil Acidity. In Methods of Soil Analysis. Part 3, Chemical Methods. SSSA No. 5, ASA, Madison, WI. Wang, J.J., A. Arceneaux, and C.W. Kennedy Response of sugarcane varieties L and HO to potassium fertilization. pp In Sugarcane Research Annual Progress Report Louisiana Agric. Exper. Station, Baton Rouge, LA. Wang, J.J., A. Arceneaux, and C.W. Kennedy Response of different sugarcane varieties to potassium fertilization. pp In Sugarcane Research Annual Progress Report Louisiana Agric. Exper. Station, Baton Rouge, LA. Wood. R.A The roles of nitrogen, phosphorus and potassium on the production of sugarcane in South Africa. Fertilizer Res. 26: Wood, A.W., R.C. Muchow, and M.J. Robertson Growth of sugarcane under high input conditions in tropical Australia. III. Accumulation, partitioning and use of nitrogen. Field Crops Res. 48:

9 Journal of American Society of Sugar Cane Technologists, Vol. 37, 2017 Table 1. Properties of soil sampled in 2005 (first- and third-ratoon) and 2007 (first- and second-ratoon) from seven locations in Louisiana planted to LCP Soil Property Cedar Grove Patout Farms Triple V1 Farms Locations KD Dugas MT Lawrence Triple V2 Farms GT Farms Soil ph P (mg kg -1 ) K (mg kg -1 ) Ca (mg kg -1 ) Mg (mg kg -1 ) S (mg kg -1 ) OM (%) Cedar Grove Plantation (2005), Patout Farms (2005), Triple V1 Farms (2005), Keith Dugas Farms (2007), Mount Lawrence Plantation (2007), Triple V2 Farms (2007, different site), Gerald Thibodeaux Farms (2007). - Soil ph, Mehlich III levels of soil phosphorus, potassium, calcium, magnesium, and sulfur, organic matter (Nelson and Sommers, 1996). 9

10 Johnson et al.: Sugar yields do not respond to phosphorus fertilizers in ratoon crops Table 2. Statistical significance (P Value) showing the effect of phosphorus fertilizer rate on cane yield, sugar yield, theoretical recoverable sugar (TRS), plant height, plant population, and phosphorus concentration in the soil profile and plant tissue. Data are averaged across seven Louisiana locations and first-, second- and third-ratoon crops. Traits P value Cane yield (Mg ha -1 ) TRS (kg Mg -1 ) Sugar yield (kg ha -1 ) Plant height (cm) Plant population (Stalks/ha) Initial Soil Phosphorus - (0-15 cm) (ppm) Final Soil Phosphorus - (0-15 cm), (ppm) Final Soil Phosphorus - (15-30 cm), (ppm) Plant Phosphorus (ppm) Phosphorus fertilizer rates = (0, 34, 50, 67, 86 kg P2O5 ha -1 ). 10

11 Journal of American Society of Sugar Cane Technologists, Vol. 37, 2017 Table 3. Response of sugarcane yield components in variety LCP to phosphorus fertilizer application. Data are averaged across seven Louisiana locations and first-, second- and third-ratoon crops. Phosphorus (kg ha -1 ) Cane Yield (Mg ha -1 ) TRS (kg Mg -1 ) Sugar Yield (kg ha -1 ) Stalk Height (cm) Population (Stalks/ha) ab ab 7, , a ab 7, , ab b 7, , b a 7, , ab ab 7, ,610 - NS NS NS - Cane yield, theoretical recoverable sugar (TRS), sugar yield, stalk height, stalk population. - Means followed by the same lower case letter within a column are not statistically different using the F probability values and the PROC MIXED macro as described by Saxton (1998) at alpha =

12 Johnson et al.: Sugar yields do not respond to phosphorus fertilizers in ratoon crops Table 4. Phosphorus levels in the soil and plant samples following phosphorus fertilizer application in variety LCP Data are averaged across seven Louisiana locations And first-, second- and third-ratoon crops. Phosphorus (kg ha -1 ) Initial Soil P (0-15 cm) Final Soil P (0-15 cm) Final Soil P (15-30 cm) Plant P mg kg b 14.2c b b 17.0bc ab b 20.4bc ab ab 23.2ab a a 27.9a ab - Initial soil phosphorus (prior to fertilizer application), Final soil phosphorus (0-15 cm, after harvest), Final soil phosphorus (15-30 cm, after harvest), Plant P = plant phosphorus (before harvest). - Means followed by the same lower case letter are not statistically different using the F probability values and the PROC MIXED macro as described by Saxton (1998) at alpha=0.05. NS 12