• Topics: Horticultural Sciences  | Beans  |  Hochmuth, George J  | Cordasco, Kim M  | Bean, snap (HS) 

A Summary of N, P, and K Research with Snapbean in Florida¹

In the 15-year period from 1982 to 1997, the land area planted to snapbeans in the state of Florida decreased 35%, yield per acre doubled from 90 to 140 bushels/acre, and total snapbean production remained about the same at 4,000,000 bushels (30 lb/bushel) (Florida Agr. Stat. Serv., 1998). Annual production figures from 1996-1997 documented that 80% of the snapbeans grown in the state come from southeast and southwest Florida including the Everglades Agricultural Area. The remaining snapbeans are grown in the north, west, and west central areas of the state. Most Florida-grown snapbeans are harvested in May and June, 40%, while 35% are harvested in November and December, and 15% in January through March. Forty percent of Florida snapbeans are shipped to other states and Canada. The 1996-1997 production value of this crop was $57,315,000, which represented 4% of the total production value of all Florida vegetable crops.

The purpose of this publication is to summarize snapbean fertilization research leading to current University of Florida recommendations for snapbean fertilization and to summarize needs for continued research. In 1995, IFAS rate recommendations for N, P₂O₅, and K₂O fertilization of snapbeans were revised upward by 20 to 40 lb/acre from those recommended in 1989 (Hochmuth and Hanlon, 1995; Kidder et al., 1989). The revised recommendations specify 90, 120, and 120 lb/acre N-P₂O₅-K₂O, respectively, as maximum rates of nitrogen (N), phosphorus (P) and potassium (K) application for soils testing very low in P and K. When test values for residual soil concentrations of P and K increase from low to very high, P₂O₅ or K₂O rate recommendations diminish from 100 to 0 lb/acre. An average of 86, 100, and 120 lb/acre N-P₂O₅-K₂O, respectively, were applied in 1994 to commercially grown snapbeans in Florida, based on a statewide USDA-administered survey of commercial farms (Fla. Agr. Stat. Serv., 1995). These applied rates were on target for N fertilization, but indicated that snapbean growers, on average, fertilize with a high rate of P₂O₅ and K₂O.

Snapbean fertilization research has been conducted in Florida for more than forty years. During this time many changes have occurred in production practices including changes in cultivars, use of nematicides, and increased plant populations. As described above, snapbean yields calculated per acre have doubled over the 15-year period from 1981 to 1996. Continued high yields are still expected with improved fertilization practices designed to not only supply adequate crop nutrient requirements but also protect the environment from nutrient pollution. Use of the Mehlich-1 (M-1) soil test, initiated in 1979, refined the practice of making fertilizer rate recommendations and resulted in a crop_ and soil-specific guide to fertilizer application. Fertilizer represented 8% of the total operating and fixed costs of snapbean production in Dade County in 1995-1996 (Smith and Taylor, 1996).

Data Summary Method

To evaluate snapbean yield response to variable rates of fertilizer, a method was needed to standardize the numerous units used for quantifying statewide yield results such as bushels or boxes/acre, hundredlb or tons/acre, and kg/hectare. Relative yield (RY), a calculated percentage, was chosen as the unit to express snapbean yield responses to fertilization. The highest yield for each fertilizer experiment was assigned a 100% value and other yields were expressed as a percentage of the highest yield. The actual yield expressed in 30 lbunits, is presented for the treatment corresponding to 100% RY. The RYs were plotted against rates of nutrient to determine how snapbean yields responded to fertilizer in Florida. The RY presentation allowed data from a variety of experiments with different cultivars, production locations, and crop seasons to be included in the graphical summary of yield responses to fertilization. For most studies, RYs of 95 to 100% were not significantly different.

Nitrogen Mixed Fertilizer Trials

It is difficult to determine specific N, P, or K responses from trials with mixed N-P-K fertilizers. Since N is the most limiting nutrient in most farming situations in Florida, responses to fertilizer in these studies are assumed to be mostly to N. These responses were not plotted, however, in Fig. 1.

Figure 1. 

Relative yield of snapbeans for experiments, years, and seasons as a function of added N.

Researchers, concerned with the repeated application of soil fumigants in the prevention of root_knot nematode, conducted a three-year spring and fall season study of the effects of two fumigants on successive crop yields (Nettles, 1953). Three nitrogen (N) forms and mixtures were studied simultaneously including, nitrate-N, ammoniacal-N, and 1:1 nitrate_ammoniacal-N from NaNO₃ and (NH₄ )₂SO_4. Fertilizer was applied at planting by hand from a 4-7-5, N-P₂O₅-K₂O blend, at the rate of 50 lb/acre N. An additional 24 lb/acre N was sidedressed after heavy rains in March 1951. Yield results were not obtained in the fall of 1951 and 1952 due to cold injury of plants.

Higher yields resulted from plants fertilized with the ammoniacal N source (293 bushels/acre) compared to nitrate fertilized plants (210 bushels/acre) in spring of 1951. Plants fertilized with ammoniacal/nitrate mixed 1:1, in spring of 1953, produced higher yields, 155 bushels/acre, than those fertilized with nitrate-N, (120 bushels/acre). The weight of a bushel was not specified in this study. An interaction between N sources and fumigant occurred in 1952. In all seasons, the lowest yields occurred with nitrate fertilized plants likely due to greater leaching losses with this nutrient form than with ammoniacal-N. Annual use of soil fumigants increased yield over unfumigated beans and did not affect successive bean plantings. The fumigants used were dichloropropane-dicloropropene mix and 41% ethylene dibromide. Yield decreases with each successive crop were attributed to repeated bean cropping over five seasons. In the absence of fumigants and nematicides, researchers in 1963 found that NH₄NO₃ increased nematode activity in snapbean plants while guano fertilized plants were least affected by nematodes (Winchester and Ozaki, 1963). Snapbean yields, however, were highest with NH₄NO₃ and guano than with NaNO₃, urea, or calcium nitrate.

Improvements in equipment used for fertilizer application prompted the study of the effects of fertilizer placement methods on yield of snapbeans (Nettles and Hulburt, 1966). Fertilizer, 6-8-8 (N - P₂O₅ - K₂O), was applied at 50, 65, and 85 lb/acre N to spring-planted beans in 1963, 1964, and 1966 near Gainesville. Five fertilizer placement methods were evaluated, including band placement 2.5 inches below the seed and to one side (single band) or to both sides of the plant row (double band), and a broadcast/band method half broadcast/ incorporated in an 18-inch band with the remainder double-banded. Double-bands were also applied in varying proportions above and below the seed, termed high and low placements, as with half of the fertilizer placed 2.5 inches to one side and 2.5 inches below the seed (high) and half-applied 2.5 inches to the other side and 6 inches beneath the seed (low) or one_fourth applied 2.5 inches below the seed (high) and three fourths applied 6 inches below the seed (low).

Snapbean yields were lower overall and were unaffected by the fertilizer placement method in 1963. Yields averaged over all placement methods were optimized with 50 lb/acre N (112 bushels/acre, 100% RY). Fertilizer placement did, however, affect yields in 1964 and 1966. Plants fertilized with the half high/half low placement method in 1964 yielded 256 bushels/acre compared to 201 bushels/acre with the broadcast/band placement method. The same broadcast/band placement method in 1966 resulted in the highest yields, 292 bushels/acre compared to 264 bushels/acre with the single- or double-band placement method. Yields in 1964 and 1966 were significantly higher, 5% probability, with 85 lb/acre N (259 and 286 bushels/acre, 100% RY, respectively) than with 50 lb/acre N, 73% and 93% RY, respectively.

Nitrogen

The fertilizer N or K rate to produce the highest yield of 'Kentucky 191' pole beans was sought in the spring seasons of 1964 and 1966, and fall seasons of 1964 and 1965 in Dover, Florida (Sutton et al., 1973). Nitrogen rates applied to Scranton fine sand soils were 100, 200, or 300 lb/acre from NH₄NO₃. These N rates were applied factorially with four K rates to row-seeded beans in the spring seasons and hill-seeded beans in the fall seasons. Fertilizer was applied in thirds at 15, 35, and 50 days after planting for row-seeded plants and divided into two applications for hill-seeded plants, one-third applied 15 days after planting and two-thirds applied 40 days after planting. All fertilizer was placed in bands 6 inches to either side of the plant row and 4 inches deep. Overhead irrigation was applied as needed.

Applied N did not significantly affect yields in either fall season or in the spring of 1966. Best yield in the spring occurred with 100 lb/acre N (205 bushels/acre, 100% RY). In the fall seasons, 100% RYs occurred with 200 lb/acre N (420 and 404 bushels/acre each season) though equally high yields also occurred with 100 lb/acre N, 96 and 99% RYs each season. Significant yield differences, 5% probability, occurred in spring 1964. Best yield this year occurred with 200 lb/acre N (260 bushels/acre, 100% RY) compared to 77% RY with 100 lb/acre N. Analysis of N concentrations in the leaf tissue revealed a lack of response to applied N in both fall 1965 and spring 1966 seasons. Late-season N concentrations in the range of 2.5% to 4% (adequate) with all rates of applied N, together with a significant (1% probability) yield to tissue concentration correlation with these N concentrations (1966), led researchers to conclude that sufficient N was present for this crop with 100 lb/acre N.

Researchers with Asgrow Seed Company conducted experiments with eight snapbean varieties on commercial farms in Homestead, Florida (Asgrow Seed Co., 1987). Snapbeans were spaced 1, 2, or 3 inches apart and evaluated for yield responses to 40, 80, or 135 lb/acre N and for the tendency of plants to lodge. Snapbean yields were similar with all N rates resulting in 94, 99, and 100% RY (218 unspecified containers/acre) with each respective N rate. Average yields were similar (226 containers/acre) from plants spaced 1 or 2 inches apart, but yields from plants spaced 4 inches apart were lower (186 containers/acre). Incidence of plant lodging increased with closer plant spacing. Researchers recommended the 2-inch plant spacing with 60 to 80 lb/acre N. Higher yielding varieties like 'Bronco', 'Podsquad', and 'Strike' had a greater tendency to lodge and researchers suggested a 3-inch plant spacing for such varieties.

While 80% of the snapbeans grown in the state are planted in the southern part of Florida, production in the north is increasing. Therefore, researchers saw a need for N fertilization research in northern snapbean production areas (Rhoads et al., 1989). Experiments were conducted with 'Strike' bushbean over spring 1987 and 1988 seasons at Quincy, NFREC, on Norfolk loamy fine sand soils. Nitrogen at 0, 60, or 120 lb/acre was applied half at the two-leaf stage and half five weeks after planting from NH₄NO₃ (fertilizer placement method was not described).

Snapbean yields were optimized with 60 lb/acre each year (169 and 96 bushels/acre, 100% RYs). These yields were significantly higher (5% probability) than yields with 0 lb/acre N, 22% and 55% RYs. Tissue N concentrations two weeks before harvest in 1987 increased linearly to 3.6% in response to N over the range of 0 to 120 lb/acre. Yields decreased to 73% and 59% each season with 120 lb/acre N compared to 60 lb/acre N. Based on these data, researchers concluded that excessive N reduces snapbean yields.

North Florida research continued at Live Oak in the spring of 1989 with a factorial experiment to evaluate two N rates and five fertilizer application programs (Hochmuth et al., 1992). Nitrogen rates of 60 or 100 lb/acre from NH₄NO₃ were applied in bands 2 inches to each side of the seed row and 3 inches below the seed or applied broadcast to simulate fertigation through a sprinkler system. Fertilizer programs 1 through 3 were equal applications; at planting, at first trifoliate leaf, and at first flower bud applied in bands only (schedule 1), banded at planting and broadcast thereafter (schedule 2), or broadcast at each application (schedule 3). Fertilizer schedules 4 and 5 were divided into 4 applications, 30% applied at planting and first bloom with 20% applied at first trifoliate leaf and first flower bud stage. All fertilizer was broadcast in these schedules except the fifth schedule where the fertilizer was banded at planting. 'Podsquad' bean seeds were planted in rows 30 inches apart.

Marketable yields of snapbeans were similar with all application programs averaging 277 bushels/acre. Leaf-tissue N concentrations increased significantly from 3.3% to 3.8% with N rates 60 to 100 lb/acre, respectively, (3.0 to 4.0% is adequate), though yields were not affected by the increase in N rate. Yields with 100 lb/acre N were 287 bushels/acre (100% RY), compared to 93% RY with 60 lb/acre N. With 100 lb/acre N, plants were larger, tended to lodge, and had more beans develop rot (38 bushels/acre) due to soil contact than those plants fertilized with 60 lb/acre N (22 bushels/acre). Researchers suspected poor root development with broadcast fertilized plants since significantly more plant lodging occurred with this placement method compared to plants that received all band-placed fertilizers.

Additional Live Oak experiments were conducted in the spring of 1989 and 1990 to evaluate yield responses to N rates, which increased in 40 lb/acre increments from 0 to 200 lb/acre (Hochmuth et al., 1992a). Klej fine sand soils were planted with 'Podsquad' seeds, fertilized with NH₄NO₃ which was divided in thirds, and applied in a band at planting (3 inches beside the row and 2 inches deep), broadcast at the first trifoliate leaf, and broadcast at the flower bud stage each season. The soil organic matter content was 1.7% in 1990.

Marketable yields increased quadratically both years, leveling off above 120 lb/acre N (279 and 322 bushels/acre each year, 100% RYs). Minimum N requirements, described by the linear-plateau model, were 73 lb/acre in 1989 and 92 lb/acre in 1990, with r² values of 0.83 and 0.64 each respective year. The quadratic model predicted optimum yield with 150 lb/acre N, and a r² of 0.66. Leaf tissue N concentrations increased linearly to 4.4% with the highest N rate in 1989 and quadratically in 1990. With plateau N rates of 73 and 92 lb/acre, corresponding leaf tissue N concentrations of 3.6 and 3.8% were in the adequate range of 3.5 to 4.0% at full-bloom sampling (Hochmuth et al., 1991). Marketable yields failed to increase above 120 lb/acre but, at this N rate, plant lodging became increasingly severe in both seasons, and yield losses above 20 bushels/acre resulted from decay after bean contact with the ground. Other quality characteristics were affected by higher N rates in 1989, but not in 1990, such as increased incidence of broken and pin (undersized) pods, (58 bushels/acre with 120 lb/acre N), and increased incidence of curved pods with higher N rates.

Researchers experimented with the humate compound "Grow-Plex SP" (Earthgreen Products Inc., Dallas TX) and rates of N in the spring (Hochmuth, 1997a) and fall of 1997 (Hochmuth, 1997b). Researchers assessed the effects of humate and N on early plant vigor and yield in both experiments conducted at the University of Florida Horticultural Research Unit near Gainesville. All plants fertilized with N received 20 lb/acre NH₄NO₃- N broadcast and incorporated preplant in a raised bed as a portion of the total applied N. The balance of the applied N to reach total rates of 0, 23, 45, 68, or 90 lb/acre was applied as a side-dress application. Total N rates were calculated as 0, 25, 50, 75, or 100% of the 90 lb/acre recommended N rate.

In spring 1997, seed furrows (two per bed with beds on 4-ft centers) were sprayed with Grow-Plex SP humate in suspension with water and Earthgreen Synfactant at rates of 0, 1, or 2 lb/acre humate. 'Caro' snapbean seeds were planted, covered immediately, and wet with overhead irrigation. Side-dressed fertilizer was applied in a band between the double rows at first trifoliate leaf and when plants were 4 inches tall. Soil moisture was maintained at -10 cb using tensiometers and overhead irrigation. Due to a loss of 20% of the plots from an overspray of herbicide, an analysis of variance was not performed on the data. Early plant vigor was rated from 1 to 5 for yellow to dark green before emergence of the trifoliate leaf. Results were similar over all humate treatments averaging a 3.7 vigor rating. Yields were similarly unaffected by humate treatment averaging 227 bushels/acre with 0 to 2 lb/acre humate. Yields were similar with 68 lb/acre N or the recommended 90 lb/acre N, 272 and 276 bushels/acre (100% RY), respectively.

In fall 1997, humate immersed in water was sprayed in furrows seeded with 'Seville' snapbeans. Humate and N rates were applied as in the spring with two foliar applications of 0, 1, or 2 lb/acre humate made at first flower bud and again at full flower with the 68 lb/acre N treatment only. Two fertilizer side-dress applications, timed as before, were broadcast between the seed rows and incorporated with a rake this season. Overhead irrigation was maintained as in the spring. Foliar application of humate late in the season had little effect on plant vigor compared to those plants that received humate in the furrow only with the 68 lb/acre N treatment. The overall effects of humate on snapbean yield were minimal, though responses to humate were noted with lower rates of applied N, optimum yield occurred with 90 lb/acre N (234 bushels/acre, 100% RY) regardless of the humate applied at planting. Significant, 1% probability, yield differences resulted with increasing N rates as yield doubled with the application of 90 lb/acre N compared with the 0 lb/acre N treatment.

Snapbean fertilization experiments were conducted each winter from 1993 to 1995 in Homestead, Florida (Hochmuth et al., 1998). Five studies were conducted (one in 1993-1994 and two each in 1994-1995 and 1995-1996 seasons) on Rockdale soils. Nitrogen was applied by banding to side of row at plant emergence (50% of total N) and again when plants were 2 to 3 inches tall (50%). Snapbeans were planted in rows approximately 30 inches apart and irrigated by overhead sprinkler (portable gun or linear-move system). Nitrogen was applied from 0 to 160 lb/acre in increasing 40 lb/acre increments. Yields did not respond to N fertilization in three experiments where average yields were 234, 281, and 368 bushels/acre. In other seasons, N reduced yields (5% probability) from 100% RY with zero lb/acre N (252 bushels/acre) to 81% RY with 160 lb/acre N, or N increased yields (5% probability) from 78% RY with zero lb/acre N to 100% RY (234 bushels/acre) with 160 lb/acre N. Factors generally not affected by N fertilization were plant stand, yields of rotten pods, and yields of misshapen snapbeans. Nitrogen reduced (1% probability) the yield of undersized beans in one experiment and had an effect on small snapbean yields in two other experiments, though the responses did not fit a specific trend. Researchers in these experiments noted that, at lower N rates, fruit set increased, but fewer fruits reached maturity. Yield responses with the grower treatments, ranging from 70 to 100 lb/acre N, were similar to those with the experimental N rates. Leaf N concentrations were sufficient or above sufficiency with all treatments in all experiments.

Nitrogen Summary

Research (65%) with N fertilization of snapbeans was conducted mainly in the northern and central regions of the state, 65%, during the spring planting season with the remaining 35% of research conducted in the southern region where 80% of snapbean production occurs. Yields were generally optimized with N rates between 60 and 100 lb/acre. These experiments are presented graphically Fig. 1 where the dashed line indicates the current recommended rate of 90 lb/acre N. In experiments where N was applied above 100 lb/acre, yields were not affected, optimized between 120 and 200 lb/acre in 30% of experiments, or decreased in three experiments. Nitrogen rates at 100 lb/acre and above resulted in larger plants with a greater tendency to lodge and produce more rotten beans due to ground contact. Plant lodging could be reduced with heavier yielding varieties like 'Bronco', 'Podsquad', and 'Strike' if plants were spaced 3 inches apart. Optimum N rates, as determined by a linear-plateau model, were 73 and 92 lb/acre in two experiments at Live Oak, Florida. Snapbean plants were negatively affected by broadcast-placed fertilizers. A greater tendency toward plant lodging resulted with broadcast-fertilized plants, possibly due to poorer root development, compared to band-fertilized plants. With this unmulched crop, researchers recommended split-fertilizer applications, part applied at planting, and the remaining N side-dressed in bands at least once early in the growing season. Plants fertilized with ammonium-containing N fertilizer produced higher yields, compared to fertilizers made from 100% of the more readily leached NO₃-N.

Phosphorus and Potassium Soil Testing

Knowledge of soil nutrient levels, particularly P and K, before planting is the starting point to predicting crop response to varying rates of applied nutrient. Using soil testing to determine preplant soil nutrient concentrations provides information so research results may be reviewed for the degree of support of existing fertilization recommendations. The Mehlich-1 (double-acid) solution is the current exractant used by Florida and several other southeastern US states for sandy soils.

Mehlich-1 extractant indices (expressed as ppm soil-extracted nutrient) are classified as very low, low, medium, high, and very high, and a crop specific fertilizer recommendation is made from that classification (Hochmuth and Hanlon, 1995). The M-1 solution became the accepted extractant standard in 1979 at the University of Florida. Previous to M-1, ammonium acetate and water extractants were used. Indices recorded from these methods cannot be directly equated with M-1 indices or fertilizer recommendation rates but review of research results from studies with these extractants presents a profile of crop response to fertilizer under varying conditions. The effects of water management, fertilizer source, fertilizer placement, and time of application, on the nutrient management system should also be considered in P and K fertilization programs

Phosphorus

Plant P uptake and yield were evaluated following application of five P fertilizers at P₂O₅ rates of 0, 45, 90, or 140 mg/2.2 lb of soil (0, 91, 182, or 272 lb/acre P₂O₅) (Rhoads, 1991). The experiment with 'Strike' bush beans occurred in the spring of 1988 in Quincy, at the North Florida Research and Education Center. Plants were grown in a glasshouse in pots filled with 13 lb of Norfolk loamy fine sand soil taken from the Ap horizon. Soils were considered deficient in P and a M-1 soil test of the check treatment after harvest resulted in 2.5 ppm P, a very low soil P concentration. Researchers sought to evaluate yield responses to ammonium containing P fertilizers: ammonium polyphosphate (APP), monoammonium phosphate (MAP), and diammonium phosphate (DAP) with calcium containing P fertilizers: superphosphate (SP), and concentrated superphosphate (CSP).

Plant P uptake (the product of dry matter yield of five-week-old plants and tissue P concentration) was greatest with APP- fertilized plants, intermediate with OSP- and TSP-fertilized plants, and least with MAP- and DAP-fertilized plants. Residual soil P concentrations at harvest reflected plant P uptake. The lowest residual M-1 P index, the greatest P uptake, and the highest dry matter yield was from APP-fertilized plants where average dry matter yield was 7 times higher than with the zero P check treatment. High dry matter yields with all treatments occurred with 140 mg/kg of P₂O₅. Significantly lower plant P uptake, highest residual M-1 soil P, and a low average dry matter yield (only 3 times above dry matter yield with the check treatment) occurred with DAP fertilized plants. Plants fertilized with P sources MAP, OSP, and TSP resulted in average dry matter yields 4, 5, and 7 times greater, respectively, than dry matter yield of plants with the check treatment. Researchers concluded that P availability from MAP and DAP was 50% lower than with other P sources.

In the spring of 1991 at the same Quincy site, P research continued with 'Strike' glasshouse-grown bush beans in pots with 4.4 lb of Norfolk loamy fine sand soil (Ap horizon) (Rhoads et al., 1993). A remaining question was the effect of soil on the availability of P. Application of P in forms unavailable to the crop present an environmental concern where these fertilizers can potentially be leached or carried off by erosion to lakes and streams. Researchers chose TSP, which was found in the previous experiment to be a readily available P fertilizer, and DAP, which was found to be a lesser available P fertilizer source. Calcite lime (fine) was applied at 2 grams/2.2 lbs of potted soil either four weeks before P application or four weeks after P application. Eighteen separate treatments including P₂O₅ rates of 90, 180, or 280 mg/2.2 lb of soil, two P sources, and lime applied before or after P application, were used to determine the effect of lime reaction with the soil or P reaction with the soil on P availability from TSP or DAP. All P treatments were incubated for four weeks with moist soil before planting. No P was applied in two additional treatments on limed and unlimed soil.

The shoots and roots of plants were collected 6.5 weeks into the season and dried to a constant weight. Plants fertilized with TSP at the highest P rate had over 100% more dry-shoot matter than DAP-fertilized plants and had 70% higher shoot P concentrations averaged over all lime and P treatments than DAP-fertilized plants. Addition of lime before TSP application, with the highest P rate, increased P uptake 16% over plants that received lime after TSP application. Lime applied before DAP, with the highest P rate, increased P uptake in shoots 85% over plants that received lime after DAP application. As with the previous study, TSP supplied more available P than DAP.

No P fertilizer was applied to plots containing soil of varying M-1 soil P concentrations during spring 1987and 1988 field experiments conducted in Quincy at the North Florida Research and Education Center (NFREC) (Rhoads et al., 1989). 'Strike' snapbeans were planted in April each year and yield and post_harvest plant tissue P concentrations were analyzed to determine the optimum soil P concentration required for bush snapbean on Norfolk loamy fine sand soils. Preplant soil P concentrations in the test plots determined by M-1 soil test were 7, 11, 29, and 66 ppm P in 1987, and 7, 12, 21, and 42 ppm in 1988. One ton/acre of calcitic lime was applied in February 1988.

Snapbean yield response was quadratic in 1987 resulting in peak yield with 29 ppm M-1 soil-extracted P (169 bushels/acre, 100% RY). In 1988, yields were 40% lower and responded linearly to soil test P concentrations through 42 ppm extracted P (100 bushels/acre, 100% RY) with 96% RY with 21 ppm soil P. Researchers suspected low soil P had limited yields in 1988 based on soil test P concentrations which were lower in the later two samples than the previous season. Application of lime in the second season was also cited for lower P availability due to the formation of calcium phosphate at higher pH. Yield data for these experiments, presented graphically in Fig. 2 , accurately represented the current breaking point between soil test P interpretations of medium to high soil P concentrations as indicated by the dashed line (Hochmuth and Hanlon, 1995; Kidder et al., 1989). Optimum yields occurred above 30 ppm P and lower yields occurred with soil P indices below 30 ppm. Whole-plant tissue P concentration was correlated with yield in 1987, but not in 1988.

Figure 2. 

Relative yield of snapbeans for experiments as a function of Mehlich-1 soil-extracted P.

Phosphorus recommendations were field tested near Live Oak at the Suwannee Valley Agricultural Research and Education Center (SVREC), on Klej fine sand soils where M-1 soil P concentrations averaged 97 ppm and soil pH was 6.8 (Hochmuth et al., 1992b). These soil P concentrations were interpreted as very high and no additional P was recommended (Kidder et al., 1988). To test this recommendation, P was either not applied or applied at planting in a band 2 inches to the side of the row of 'Podsquad' beans and 3 inches deep at 50 lb/acre P₂O₅ from TSP. Application of P did not affect bean yield on these very high P soils. In addition, bean length, condition (broken or rotten), or tendency toward plant lodging were not affected by added P. Yields were not different with 0 lb/acre P₂O₅, 93% RY, or 50 lb/acre P₂O₅ (226 bushels/acre, 100% RY). These results supported the recommendation of 0 lb/acre P₂O₅ for soils very high in extracted P.

Field experiments were conducted on two commercial farms near Homestead during the winter seasons of 1994 through 1996 (Hochmuth et al., 1998). Snapbeans were grown on Rockdale soil and were sprinkler irrigated by portable gun or linear-move systems. All P from TSP was applied in a band to one side of the row at plant emergence. Soil P concentrations extracted with AB-DPTA solution before fertilization ranged from 56 to 113 ppm and were considered adequate for optimum yields. Phosphorus at rates of 0, 50, 100, 150, or 200 lb/acre P₂O₅ had no effect on yields in two experimental seasons. Average yields for these seasons were 216 and 252 bushels/acre. Yields increased slightly in two other experimental seasons (5% probability) from zero to 200 lb/acre P₂O₅ (296 to 312 bushels/acre, 100% RY) and from zero to 100 lb/acre P₂O₅ (228 to 242 bushels/acre, 100% RY). Yields decreased (5% probability) in a fifth season from 95% RY (381 bushels/acre) with zero lb/acre P₂O₅ to 85% RY with 200 lb/acre P₂O₅. Yields from these experiments are graphed in Fig. 3 . Phosphorus did not affect yields of rotten or misshapen bean pods in any experimental season and did not affect yield of undersized pods, except in one season where fewer small pods were produced with P at 200 lb/acre P₂O₅. Researchers suspected P enhanced maturity or acted to reduce fruit set and allow existing pods to develop. Additional work was suggested on the effect of P fertilization on growth, fruit set, and maturity of snapbeans.

Figure 3. 

Relative yield of snapbeans for experiments, years, and seasons as a function of added P.

Phosphorus Summary

Research with P fertilization of snapbean was conducted near Quincy and Live Oak, where future snapbean production is likely to occur, and in the Homestead area. Yields did not respond to added P on soils with high and very high M-1 soil-extracted P. These results concurred with the Institute of Food and Agricultural Sciences (IFAS) recommendation of zero lb/acre P₂O₅ on these soils (Hochmuth and Hanlon, 1995; Kidder et al., 1989). Snapbean yields increased slightly with P fertilization at two Homestead, Florida locations where AB_DPTA soil-extracted P concentrations were not available, or were 81 ppm. Yield at a third Homestead location decreased with P fertilization where soil P concentrations were 56 ppm. In other Homestead experiments, yield did not respond to applied P when AB-DPTA soil-extracted P concentrations were 113 ppm or 91 ppm. Experiments were not conducted to test snapbean yield response to applied P fertilizer on soils very low, low, and medium in extracted P, because these low-P soils were not found in the commercial snapbean farms of Dade County. Phosphorus recommendations (Hochmuth and Hanlon, 1995) for these soil P concentrations were not tested in field research. Earlier research with pot-grown snapbeans stressed the application of fertilizer sources containing readily available P. Plant P uptake and yield were highest with APP and TSP and lowest with DAP. Phosphorus not absorbed by plants can potentially be carried off by soil erosion to pollute water systems. Application of lime four weeks before P application increased P availability from DAP, but TSP remained a more readily available P source with or without early lime application. Researchers suggested additional study on the effect of P fertilization on growth, fruit set, and maturity of snapbeans based on results from an experiment where reduced yield of undersized beans occurred with added P.

Potassium

Nitrogen and K were applied factorially in the spring seasons of 1964 and 1966, and fall seasons of 1964 and 1965 to Scranton fine sand soils in Dover (Sutton et al., 1973). Yields of 'Kentucky 191' pole beans were evaluated for spring 1964 and 1966 seasons and fall 1964 and 1965 seasons following factorial applications of three N rates and three K rates, 113, 224, and 336 lb/acre K₂O from KCl. Fertilizers were applied in thirds to row-seeded beans in the spring, at 15, 35, and 50 days after planting and divided in two applications with hill-seeded beans in the fall seasons, one-third 15 days after planting and two-thirds 40 days after planting. All fertilizer was placed in bands 6 inches to either side of the plant row and 4 inches deep. Overhead irrigation was applied as needed.

Yields were not affected by K rate in any season except the fall of 1965 (Fig 4). High yield this season occurred with 113 lb/acre K₂O (463 bushels/acre, 100% RY) and decreased to 90% RY with 336 lb/acre K₂O, significant at 1% probability. A significant negative correlation, -0.479, resulted between leaf-tissue K concentrations sampled at the last half of the harvest period and yield. Researchers suspected soluble salt concentrations 3 to 4 times higher in 1965 than 1966 may have contributed to the yield reduction that season. High yields in other seasons, though yields were similar with all K rates, occurred with 113, 336, and 224 lb/acre K₂O (269, 483, and 235 bushels/acre, 100% RYs) in the spring and fall of 1964, and the spring of 1966, respectively.

Potassium research was conducted (without K fertilization) on Norfolk loamy fine sand soils at Quincy, NFREC, in 1987 and with 0, 85, or 170 lb/acre K₂O from K₂SO₄ applied preplant in 1988 (Rhoads et al., 1990). Yield responses were evaluated based on M-1 soil-extracted K concentrations which were tested before planting, February 1987, and after planting and fertilization, April 11, 1988. Yield responses in both seasons were linear increasing through 73 and 78 ppm M-1 soil-extracted K each season (169 and 101 bushels/acre, 100% RY, respectively). These K concentrations are currently interpreted as high and no additional K fertilizer would be recommended (Hochmuth and Hanlon, 1995). Graphed yield responses are presented in Fig. 4 where the dashed line indicates the current break point between interpretations of medium and high M-1 soil-extracted K concentrations. Yields were not predicted to increase at concentrations above this line, but in both Quincy experiments yields were optimized with higher soil K concentrations. Response to added K fertilizer also occurred in the plant tissue. There was greater correlation between snapbean tissue K concentration and soil K concentration in 1988, 0.90, compared to a 0.60 correlation between plant tissue and soil K in 1987 where no additional K fertilizer was applied. Although added K increased the concentration of K, as measured in the plant tissue in 1988, overall yields were lower in 1988 than in 1987.

Figure 4. 

Relative yield of snapbeans for experiments, years, and seasons as a function of added K₂O.

Where snapbean yields in the above experiments required greater amounts of soil K than those cited by IFAS, a spring 1989 experiment near Live Oak (SVAREC) required less than the recommended K rate for optimum yields (Hochmuth et al., 1992). A potassium recommendation of 80 lb/acre K₂O was made (Kidder et al., 1989) for these Klej fine sand soils which tested low, 24 ppm, for M-1 soil-extracted K. Potassium treatments were 0 or 80 lb/acre K₂O from KMgSO₄ applied preplant in a band 2 inches beside the row and 3 inches deep. 'Podsquad' snapbeans were planted on April 19. Snapbean yields responded similarly to both K treatments with 80 lb/acre K₂O (226 bushels/acre) 100% RY compared to 94% RY with 0 lb/acre K₂O. Researchers concluded that more research is needed with K fertilization of snapbean. Bean quality characteristics: straightness, length, broken, empty or rotten pods were all unaffected by the addition or omission of K fertilizer. The tendency of plants to lodge was also unaffected by K fertilization.

Experiments were conducted in Homestead, Florida to evaluate yield responses to K rates of 0, 50, 100, 150, or 200 lb/acre K₂O (Hochmuth et al., 1998). Soils used for all K studies were Rockdale soils on commercial farms with sprinkler irrigation (portable gun or linear-move) Potassium from KCl was banded to the side of the row, 50% at plant emergence and 50% when plants were 2 to 3 inches tall (with the second N application ). Soil K concentrations, tested with AB-DPTA soil extractant, ranged from 71 to 281 ppm and were considered adequate for optimum yield without additional K. Yields in three of the experiments were similar with K rates from 0 to 200 lb/acre, while yields decreased in a fourth experiment, and increased slightly in a fifth experiment with added K. Yields of small, rotten, or misshaped beans were not affected by K fertilization in any experiment, nor were plant stands affected by increased K. Whole-leaf K concentrations were above the sufficiency range in all experiments and occasionally increased with K fertilization.

Potassium Summary

Snapbean yields were not always affected by K fertilization at K rates through 336 lb/acre K₂O. Yields were not always optimized with the recommended K rate based on M-1 soil test at times requiring more than the recommended rate and at other times less than the recommended rate. This response behavior could be related to the mobility of the K ion in sandy soils, making K fertilizer prediction difficult. Potassium rate recommendations were increased for soils very low, low, and medium in M-1 soil-extracted K from 80, 80, and 60 b/acre K₂O (1989) to 120, 100, and 80 lb/acre K₂O (1995), respectively. While graphed yield responses Fig. 4 ), appear to fall as K rates increased above the recommended 120 lb/acre K₂O, indicated by the dashed line, 70% of the experiments were not affected by increased K. Yields decreased with added K in 20% of experiments, and yields were optimized with 100 lb/acre K₂O in 10% of the experiments. Based on unpredictable yield responses to residual soil K concentrations and K applied as fertilizer in the above summarized experiments, more research is needed on K fertilization of snapbean. Yields of undersized, rotten, or misshapen snapbeans were not affected by increased K fertilizer, nor were plant stands affected by increased K. As with all unmulched and overhead irrigated crops, split-N and split-K application was recommended due to the leaching potential of these mobile nutrients. Researchers recommended preplant application of 25% to 50% of the N and K fertilizer with the remaining N and K fertilizer applied in sidedress bands early in the season.

Summary

For snapbeans, no yield advantage resulted from application of N in excess of recommended rates in experiments in north Florida. Plant lodging increased with N application above 100 lb/acre due to larger plant size with high N. Yield losses occurred when beans touched the soil and developed rot. The tendency toward plant lodging increased with broadcast N application compared with plants fertilized with band applied N. Statistical analysis and leaf tissue correlation with yield resulted in a range of optimum N rates between 73 to 100 lb/acre, which approximated the 90 lb/acre N currently recommended by IFAS for this crop. With N and K fertilization, researchers recommended split application of these nutrients: part applied preplant and part as an early-season side-dress due to leaching with this unmulched, overhead irrigated crop.

Phosphorus soil concentrations of 16 to 30 ppm, measured by M-1 soil test, were sufficient to produce optimum yields over two experiment seasons, though IFAS recommends addition of 80 lb/acre P₂O₅ for soils with these P concentrations. Snapbeans grown on soils with P concentrations greater than 30 ppm produced optimum yields without added P fertilizer confirming IFAS recommendations. Additional research with P fertilization of snapbean is needed on soils with very low and low M-1 P concentrations. Research is also needed at larger commercial scale farms to test nutrient and irrigation management programs in the commercial setting.

Yields of snapbean plants fertilized with K were generally not significantly affected by increases in rates of this nutrient above those currently recommended. Researchers recommend no K application where soil K concentrations are above 60 ppm as tested by M-1 extractant but, in two experiments, snapbean yields responded linearly to soil K concentrations through 73 and 78 ppm. Additional research is needed with this highly mobile nutrient to determine K rate recommendations for snapbean.

Literature Cited

Asgrow Seed Co. 1987. Fresh market beans. Nitrogen and spacing response. Misc. publ. WBC/5-19-87.

Florida Agricultural Statistics Service. 1998. Florida Agricultural Statistics - Vegetable Summary 1996-97. Fla. Agric. Stat. Serv., Orlando, FL.

Hochmuth, G., D. Maynard, C. Vavrina, and E. Hanlon. 1991. Plant tissue analysis and interpretation for vegetable crops in Florida. Fla. Coop. Ext. Serv. Spec. Ser. SS-VEC-42.

Hochmuth, G. J., B. Hochmuth, and E. Hanlon. 1992. Comparison of various N scheduling methods for snapbeans. Fla. Agr. Expt. Sta. Res. Rep., Suwannee Valley AREC 92-8.

Hochmuth, G., B. Hochmuth, and E. Hanlon. 1992a. Response of snapbean to nitrogen fertilization on a sandy soil. Fla. Agr. Expt. Sta. Res. Rep., Suwannee Valley AREC 92-6.

Hochmuth, G., B. Hochmuth, and E. Hanlon. 1992b. Field test of IFAS P and K recommendations for snapbeans. Fla. Agr. Expt. Sta. Res. Rep., Suwannee Valley AREC 92-15.

Hochmuth, G. J., and E. Hanlon. 1995. IFAS standardized fertilization recommendations for vegetable crops. Fla. Coop. Ext. Serv. Circ. 1152.

Hochmuth, G. 1997a. Response of sweet corn and snapbean to Growplex humate. Fla. Agr. Expt. Sta. Res. Rep., Suwannee Valley AREC 97-7.

Hochmuth, G. 1997b. Snapbean and sweet corn response to N rate and furrow-placed Growplex humate. Fla. Agr. Expt. Sta. Res. Rep., Suwannee Valley AREC 97-21.

Hochmuth, G., E. Hanlon, S. O'Hair, J. Carranza, and M. Lamberts. 1998. Report to S. Fla. Water Mgt. Dist. (draft).

Montelaro, James. 1978. Commercial vegetable fertilization guide. Fla. Coop. Ext. Serv. Circ. 225-B.

Nettles, V.F. 1953. Yield responses of beans to repeated use of soil fumigants and three sources of nitrogen. Proc. Amer. Soc. Hort. Sci. 62:320-324.

Nettles, V.F., and W. C. Hulburt. 1966. Effect of placements and levels of fertilizer on the yield of vegetables. Proc. Fla. State Hort. Soc. 79:185-191.

Rhoads, F. M., E. A. Hanlon, Jr., S.M. Olson, and G. J. Hochmuth. 1990. Response of snapbean to N-rates and soil-test P and K. Soil Crop Sci. Soc. Fla. Proc. 49:10-13.

Rhoads, F. M. 1991. Phosphorus source, soil-test P, snapbean growth, and P uptake. Soil Crop Sci. Soc. Fla. Proc. 50:122-124.

Rhoads, F. M., E. A. Hanlon, and S. M. Olson. 1993. Phosphorus availability to snap beans as affected by lime sequence and phosphorus source. Soil Crop Sci. Soc. Fla. Proc. 52:90-94.

Sutton, P., E. E. Albregts, and C.M. Howard. 1973. Influence of N and K on pole bean (Phaseolus vulgaris L.) response and soil and plant analysis. Soil Crop Sci. Soc. Fla. Proc. 32:136-137.

Winchester, J. A., and H. Y. Ozaki. 1963. Some effects of nitrogen source on beans and peppers growing in root-knot infested soil. Proc. Fla. State Hort. Soc. 76:163-168.

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