Phosphorus Index Research Articles

Environmental Concerns of Phosphorus Management in Potato Production

Phosphorus (P) losses from agricultural systems are a cause of degraded surface water quality of lakes and streams. In freshwater systems, P is often the most limiting nutrient for algae growth and an increase in P additions to these systems can cause a shift in ecology. These shifts can result in a degradation of the water resource as habitat or for recreation. In an effort to combat the negative effects of agriculture management practices on surface water quality, federal and state regulations require some level of assessment to guide P applications. Areas with large amounts of potato production are of particular concern with respect to P loss since potatoes are a high P demanding crop and are inefficient users of applied P. In many cases, soils in potato production are managed with a higher soil test P concentration compared to other crops and P applications for optimum production exceed P removal. When potato production fields are maintained at high soil test P levels, this may increase the risk of P loss in runoff. However, based on soils and landscape positions where potatoes are grown, there may be little risk of transport. While there appears to be little risk of P loss on low-sloping, sandy soils, output from the Wisconsin Phosphorus Index suggests that more steeply sloping fields can pose some risk, especially when soil test P concentrations exist at above optimum levels. At high soil test P levels, no P may be required for optimum yield in rotated crops, but production practices of these crops may need to be altered to reduce P losses. Furrow-irrigated and tile-drained fields may also pose risks of P loss to the environment. While the P demands of potato are greater than those for most crops, it is likely that most of this P will not be exported via surface runoff. Careful management considerations must be made when producing potatoes on high sloping soils, especially those close to surface water bodies. Future considerations of P management and water quality will focus on assessing leaching risk of P and this contribution to surface waters.

Factors Associated with Calcium Absorption in Postmenopausal Women: A Post Hoc Analysis of Dual-Isotope Studies

Reduced calcium absorption is a risk factor for osteoporosis. This study examined factors associated with fractional calcium absorption (FCA) and net calcium absorption in postmenopausal women in a post hoc analysis of three completed dual-isotope studies. Data were analyzed from 50 postmenopausal women undergoing 121 inpatient research visits in three studies evaluating changes in FCA related to correction of vitamin D insufficiency (n=19), use of proton pump inhibitors (n=21), and use of aromatase inhibitors to treat breast cancer (n=10). Net calcium absorption was the product of FCA and total calcium intake in milligrams per day. Variables included subjects' age, race, body mass index, serum calcium, creatinine, parathyroid hormone, 1,25-dihydroxyvitamin D, 25-hydroxyvitamin D, and habitual intake of kilocalories, protein, fat, carbohydrate, fiber, calcium, iron, magnesium, oxalate, phosphorus, potassium, and vitamin D based on outpatient diet diaries. In multivariate models, subjects' age, dietary intake of kilocalories, carbohydrates, fat, fiber, calcium, and potassium were significant predictors of FCA. In multiple variable models predicting net calcium absorption, dietary intake of kilocalories, fat, fiber, calcium, potassium, and serum 1,25-dihydroxyvitamin D were significant. The square of the correlation between actual and predicted values (an approximation of R2) was 0.748 for FCA and 0.726 for net calcium absorption. Similar to other studies, this study found that age, 1,25-dihydroxyvitamin D, and dietary calcium and fat were associated with calcium absorption. Dietary intake of kilocalories, carbohydrates, and potassium were new factors that were significantly associated with FCA and net calcium absorption. In summary, the study suggests that several dietary habits play a role in calcium absorption, beyond vitamin D and calcium.

Ontario’s Nutrient Calculator: Overview and Focus on Sensitivity Analysis

The long-term build-up of nutrients in agricultural fields has contributed to surface and ground water quality problems in many jurisdictions. The Ontario government has required the use of a decision support system, entitled NMAN, to develop nutrient management strategies for new or expanding livestock facilities. The NMAN software adds nutrient (N and P) sources (commercial fertilizer, manure, crop residual, grazing) and subtracts nutrients lost through crop removal and runoff to calculate the assimilative capacity on a field-by-field basis. NMAN is designed to help guide nutrient management at the farm-scale and to prevent the long-term build-up of nutrients in agricultural soils. However, success ultimately rests with the farmers’ willingness to use NMAN on a continuing basis for determining nutrient application rates. While several factors are shown to influence the use agricultural decision support systems, perceived usefulness or value is key. In an effort to inform users about the NMAN software, we provide a brief description and sensitivity analysis of selected input variables. The newest version, NMAN3, is more intuitive than earlier versions, and it is easier to navigate and to modify parameters. Using a sample nutrient management strategy, we determine the sensitivity of output parameters to changes in the input variables. We primarily focus on the Phosphorus (P) Index, which measures a potential P loss from agricultural fields. The results indicate that the some parameters used in NMAN3, i.e. slope percentage, slope length, etc., need to be accurately measured, and that agency officials should be aware of these parameters during site visits and/or inspections.

Plant phosphorus availability index in rehabilitated bauxite-processing residue sand

Background and aims Soil phosphorus (P) indices that have been originally developed and applied to agricultural soils for predicting P uptake by plants were examined in a pot experiment to determine the most suitable index for P availability in bauxite-processing residue sand (BRS).

Applicability of phosphorus site indices to wastewater effluent-irrigated cropland

Phosphorus (P) indices, originally developed to assess the risk of P export to aquatic systems from agricultural fields receiving inorganic fertilizers and livestock manures, are being used for other P sources with different characteristics and methods of application. This study determined Pennsylvania P index scores for eleven crop fields of Penn State University9s Living Filter system receiving 130 kg P2O5 ha−1 (115 lb P2O5 ac−1) in 2008 via sprinkler irrigation of municipal wastewater effluent. A baseline assessment of P index treated effluent irrigation as surface application of completely soluble P source material with maximum potential of runoff P loss. Three fields located ≤22 m (200 ft) from streams ranked high and very high in P loss rating under baseline assessment. Modified assessments involved changing the application method multiplier and P source coefficient to more accurately reflect the year-round intermittent application of P via sprinkler irrigation. All fields were ranked as having low risk of P export using the modified parameters. Site monitoring data from nearly 50 years of effluent irrigation show no evidence of excess P transport to groundwater or off-site surface water, suggesting that baseline assessment might be overestimating P loss rating of some fields. Results underscore the need to tailor P indexing tools to address the differential risk of P loss for specific P sources and application methods.

Estimation of Maximum Biosolids and Meat and Bone Meal Application to a Low P Index Soil and a Method to Test for Nutrient and Metal Losses

The aim of this study was to develop (1) a method for the calculation of the maximum legal rate at which meat and bone meal (MBM) and biosolids should be applied to land, which took into account the soil phosphorus (P) index, the dry solids and the nutrient and metal content of each material, and (2) a quick method to evaluate their impact, when applied at the estimated maximum and twice the maximum application rates, on the release of P and metals to surface runoff. Three types of biosolids—lime stabilised (LS), anaerobically digested (AD) and thermally dried (TD)—and two types of MBM (low and high ash) were examined. The nutrient and metal losses were examined using a 1-L capacity beaker, which contained an intact soil core. Treatments were applied at maximum and twice the maximum legal application rates and then overlain with 500 mL of water, which was stirred to simulate overland flow. At the maximum legal application rate, low ash MBM (1.14 mg L−1) and TD biosolids (2.43 mg L−1) had the highest losses of P. Thermally dried biosolids and LS biosolids exceeded maximum allowable concentrations (MAC) for manganese, but all treatments remained below the MAC for copper and iron, at the maximum legal application rate. Anaerobically digested biosolids and high and low ash MBM would appear to have potential for landspreading, but these results are indicative only and should be verified at field scale.

A phosphorus index for use in intensive irrigated areas

AbstractIn irrigated semi‐arid areas, nutrient pollution from agriculture from irrigation return flows is one of the most important surface water quality problems and can lead to eutrophication. In this study, a new phosphorus index called IPreg has been adapted as a management tool for application to irrigated farming systems and then applied within ‘Las Filadas’ drainage basin (Spain) at a plot scale. Two new transport factors related to the irrigation management system were introduced: (i) the seasonal irrigation performance index and (ii) the efficiency of the mean irrigation dose that represents average water losses below the root zone when an average irrigation dose is applied. IPreg includes 10 factors, three of which account for P availability in the soil and seven for P transport processes. The results indicate that 18% of the study area had a high to very high risk of phosphorus loss and 60% at medium risk. Corn and alfalfa had the highest IPreg values under intense irrigation and high fertilizer application rates. IPreg was also higher in phosphorus‐rich soils and in plots treated with organic manure, especially pig slurry.

Validation and modification of the phosphorus loss index as applied to a small catchment

AbstractEnvironmental legislation in many countries requires the development of phosphorus indices to determine the risk of P loss from soils to water. The concentrations of total phosphorus (TP), molybdate‐reactive phosphorus (MRP) and particulate phosphorus (PP) and the movement of these P forms were determined in a small catchment in Galicia (north–west Spain) with the aim of establishing an index of P loss. The discharges and concentrations of the different P forms were measured at different points in the river basin. The information was used to estimate the accuracy of a P index derived from the model described by Gburek et al. (2000). The amount of P lost over the 5‐month period of study was ca. 60 g/ha; in essence, the overall loss was low. The P losses differed throughout the study period and between sampling points, and some areas of the catchment acted as P sinks. This was probably associated with the transport of deposited material by the rivers. Of the two components included in the index, the source factor was consistent with the source areas in the catchment as identified by water analysis. However, the transport factor was not very consistent with the field data and must be reconsidered.

Impact evaluation of a pisciculture in the Tucuruí reservoir (Pará, Brazil) using a two-dimensional water quality model

► We modeled the Tucuruí reservoir, Brazil, for assess phytoplankton growth. ► Simulations were carried out in low and high rainfall periods, by using CEQUAL-W2. ► We reproduced horizontal and vertical gradients, temporal and spatial variability. ► Model showed chlorophyll a is a key factor to define the system’s trophic status . ► Model can simulate several scenarios, by changes in reservoir management . The Tucuruí reservoir, Pará State, Brazil, has one of the largest flooded areas in Brazil and its viability for aquaculture is being evaluated by local government in pilot projects. In this context, the purpose of this study is to assess the impact of a pisciculture in the water quality of the reservoir, by combining field data with model simulations. Hydrodynamics and water quality was modeled using CE-QUAL-W2. The model was validated using about 5 years of field data of temperature, nitrate, ammonia, phosphorus, total suspended solids (TSSs), dissolved oxygen and chlorophyll a . The model was able to reproduce horizontal and vertical gradients and their temporal variability. After validation, the model was used to simulate the response of water quality to various management scenarios of the pisciculture. Results show that solely based on phosphorus index, an increase of 30% occurs from 2007 to 2011, and at least 10% from 2008 to 2011. Based on this, the system tends to change its trophic state from oligotrophic to mesotrophic. However, if we consider chlorophyll a (Chl a ) as an indicator, no change in the trophic state is observed, since even with a 100% increase of the phosphorus load, the concentration of Chl a remains oligotrophic (<4 μg/L) during the simulated period. Thus, the model results suggest that Chl a should be used as the key indicator to assess the trophic state of the system, since the nutrients may be in excess in the environment without promoting primary production.

A phosphorus index that combines critical source areas and transport pathways using a travel time approach

Summary Spatially distributed nonpoint source (NPS) pollution indices are used to identify areas in a watershed where potential pollutant loading coincides with runoff generating areas. However, most such indices either ignore the degree of hydrologic connectivity to the stream network or they estimate it based simply on the distance of the pollution generating area from an open channel. We propose an NPS pollution index based on runoff travel times from saturated variable source areas (VSAs) to the natural stream network as a means for including hydrologic connectivity between source areas and streams. Although this method could be generalized to any pollutant transported by storm runoff, here we focus on phosphorus and refer to the index as the travel-time phosphorus index (TTPI). The TTPI was applied to a 38 km2 agricultural watershed in central New York and shown to yield realistic, spatially explicit predictions of critical phosphorus loading areas and routing pathways. One interesting finding is the potential role of man-made drainage networks (e.g., road- or agricultural-ditches) in NPS pollution and the possibilities of targeting water quality protection practices around or within these networks. Because the technique is GIS-based, relatively simple to apply, uses readily available geospatial data, and the theoretical underpinnings are transparent, it can provide a useful screening tool for water resource managers charged with the identification and remediation of critical NPS pollution source areas.

Accounting for the Risks of Phosphorus Losses through Tile Drains in a Phosphorus Index

Tile drainage systems have been identified as a significant conduit for phosphorus (P) losses to surface water, but P indices do not currently account for this transport pathway in a meaningful way. Several P indices mention tile drains, but most account for either the reduction in surface runoff or the enhanced transport through tiles rather than both simultaneously. A summary of the current state of how tile drains are accounted for within P indices is provided, and the challenges in predicting the risk of P losses through tile drains that are relative to actual losses are discussed. A framework for a component P Index is described, along with a proposal to incorporate predictions of losses through tile drains as a component within this framework. Options for calibrating and testing this component are discussed.

Comparing Phosphorus Indices from Twelve Southern U.S. States against Monitored Phosphorus Loads from Six Prior Southern Studies

Forty-eight states in the United States use phosphorus (P) indices to meet the requirements of their Natural Resources Conservation Service (NRCS) Code 590 Standard, which provides national guidance for nutrient management of agricultural lands. The majority of states developed these indices without consultation or coordination with neighboring states to meet specific local conditions and policy needs. Using water quality and land treatment data from six previously published articles, we compared P loads with P-Index values and ratings using the 12 southern P indices. When total measured P loads were regressed with P-Index rating values, moderate to very strong relationships (0.50 to 0.97) existed for five indices (Arkansas, Florida, Georgia, North Carolina, and South Carolina) and all but one index was directionally correct. Regressions with dissolved P were also moderate to very strong ( of 0.55 to 0.95) for the same five state P indices (Arkansas, Florida, Georgia, North Carolina, and South Carolina); directionality of the Alabama Index was negative. When total measured P loads were transformed to current NRCS 590 Standard ratings (Low [<2.2 kg P ha], Moderate, [2.2-5.5 kg P ha], and High [>5.5 kg P ha]) and these ratings were then compared to the southern-Index ratings, many of the P indices correctly identified Low losses (77%), but most did not correctly identify Moderate or High loss situations (14 and 31%, respectively). This study demonstrates that while many of the P indices were directionally correct relative to the measured water quality data, there is a large variability among southern P indices that may result in different P management strategies being employed under similar conditions.

Phosphorus Index as a Phosphorus Awareness Tool: Documented Phosphorus Use Reduction in New York State

In 1999, New York introduced its concentrated animal feeding operation (CAFO) permit followed, in 2001, by release of the New York phosphorus index (NY-PI) and establishment of a statewide on-farm research partnership. State policy requires that the Natural Resources Conservation Service's 590 nutrient management standard, and therefore the NY-PI, be implemented on all CAFO farms as well as animal feeding operations (AFOs) receiving state or federal cost share funds for manure storage and other related practices. Since the introduction of the NY-PI, P fertilizer sales (farm use) declined from 14,470 Mg in 2001 (8.6 kg P ha) to 7,376 Mg in 2009 (5.0 kg P ha). Cost of fertilizer was not a significant covariate for the reduction in P use over time. Certified nutrient management planners were surveyed in 2011 to evaluate their perceptions of drivers for changes in P use. In addition, whole farm P balances were recorded for 54 New York dairy farms. The survey data illustrate key ingredients for success: (i) statewide awareness of environmental challenges through both regulations and extension programming; (ii) science-based, user-friendly tools that allow for farm-specific responses to the challenges; (iii) risk assessment of management alternatives through on-farm research; (iv) enforcement of regulations; and (v) existence of economically feasible alternatives. Whole farm balances showed a reduction in P surplus of 44%, averaged across farms, whereas milk production increased, further illustrating the willingness and economic potential to make changes that improve production efficiency and reduce risk of nutrient loss to the environment.

Phosphorus Indices: Why We Need to Take Stock of How We Are Doing

Many states have invested significant resources to identify components of their Phosphorus (P) Index that reliably estimate the relative risk of P loss and incentivize conservation management. However, differences in management recommendations and manure application guidelines for similar field conditions among state P Indices, coupled with minimal reductions in the extent of P-impaired surface waters and soil test P (STP) levels, led the U.S. Natural Resources Conservation Service (NRCS) to revise the 590 Nutrient Management Standard. In preparation for this revision, NRCS requested that a review of the scientific underpinnings and accuracy of current P Indices be undertaken. They also sought to standardize the interpretation and management implications of P Indices, including establishment of ratings above which P applications should be curtailed. Although some states have initiated STP thresholds above which no application of P is allowed, STP alone cannot define a site's risk of P loss. Phosphorus Indices are intended to account for all of the major factors leading to P loss. A rigorous evaluation of P Indices is needed to determine if they are directionally and magnitudinally correct. Although use of observed P loss data under various management scenarios is ideal, such data are spatially and temporally limited. Alternatively, the use of a locally validated water quality model that has been shown to provide accurate estimates of P loss may be the most expedient option to conduct Index assessments in the short time required by the newly revised 590 Standard.

Using a Phosphorus Loss Model to Evaluate and Improve Phosphorus Indices

In most states, the phosphorus (P) index (PI) is the adopted strategy for assessing a field's vulnerability to P loss; however, many state PIs have not been rigorously evaluated against measured P loss data to determine how well the PI assigns P loss risk-a major reason being the lack of field data available for such an analysis. Given the lack of P loss data available for PI evaluation, our goal was to demonstrate how a P loss model can be used to evaluate and revise a PI using the Pennsylvania (PA) PI as an example. Our first objective was to compare two different formulations-multiplicative and component-for calculating a PI. Our second objective was to evaluate whether output from a P loss model can be used to improve PI weighting by calculating weights for modified versions of the PA PI from model-generated P loss data. Our results indicate that several potential limitations exist with the original multiplicative index formulation and that a component formulation is more consistent with how P loss is calculated with P loss models and generally provides more accurate estimates of P loss. Moreover, using the PI weights calculated from the model-generated data noticeably improved the correlation between PI values and a large and diverse measured P loss data set. The approach we use here can be used with any P loss model and PI and thus can serve as a guide to assist states in evaluating and modifying their PI.

Evaluation of Phosphorus Indices after Twenty Years of Science and Development

The P Index was proposed as a nutrient management tool in 1992 and has been implemented as such for the past decade. However, lack of water quality improvement in agricultural watersheds and discrepancies in P loss ratings between P indices have raised questions about continued use of the P Index. In response to these concerns, a symposium was held as part of the 2011 ASA, CSSA, SSSA annual meetings. This symposium produced a special collection of seven papers describing the role of P indices in P management, evaluation of P indices, new models for assessing P loss, methods to improve P indices, and changes in producer behavior resulting from P Index use. The objectives of this introductory paper are to provide background on the P Index concept, overviews of the special collection papers, and recommendations for future P Index evaluation and development research. The papers in this special collection conclude that P indices can provide accurate assessments of P loss but must be evaluated appropriately. Evaluation will require compiling large regional P loss datasets at field and small watershed scales. Simulation models may be used to generate P loss estimates; however, models must be calibrated and validated to ensure their accuracy. Further development of P indices will require coordinated regional efforts to identify common P Index frameworks and standardized interpretations. Stringent P Index evaluations will expand the utility of P indices for critical source area identification and strategic best management practice implementation by regulatory, education, and scientific communities alike.

Testing the Wisconsin Phosphorus Index with Year-Round, Field-Scale Runoff Monitoring

The Wisconsin Phosphorus Index (WPI) is one of several P indices in the United States that use equations to describe actual P loss processes. Although for nutrient management planning the WPI is reported as a dimensionless whole number, it is calculated as average annual dissolved P (DP) and particulate P (PP) mass delivered per unit area. The WPI calculations use soil P concentration, applied manure and fertilizer P, and estimates of average annual erosion and average annual runoff. We compared WPI estimated P losses to annual P loads measured in surface runoff from 86 field-years on crop fields and pastures. As the erosion and runoff generated by the weather in the monitoring years varied substantially from the average annual estimates used in the WPI, the WPI and measured loads were not well correlated. However, when measured runoff and erosion were used in the WPI field loss calculations, the WPI accurately estimated annual total P loads with a Nash-Sutcliffe Model Efficiency (NSE) of 0.87. The DP loss estimates were not as close to measured values (NSE = 0.40) as the PP loss estimates (NSE = 0.89). Some errors in estimating DP losses may be unavoidable due to uncertainties in estimating on-farm manure P application rates. The WPI is sensitive to field management that affects its erosion and runoff estimates. Provided that the WPI methods for estimating average annual erosion and runoff are accurately reflecting the effects of management, the WPI is an accurate field-level assessment tool for managing runoff P losses.

The effects of fertilizer applications on runoff loss of phosphorus

The phosphorus index (PI) can be used to effectively identify areas with high risks of phosphorus losses. Manures and fertilizers are important source factors for the establishment of the PI system. An artificial precipitation experiment was performed to evaluate phosphorus losses with the applications of different types of fertilizers and manures. The results showed that the total phosphorus (TP) losses in runoff followed the order of ammonium phosphate monobasic (NH4H2PO4), ammonium hydrogen phosphate ((NH4)2HPO4), monobasic potassium phosphate (KH2PO4), chicken manure, and cattle manure with surface application of these fertilizers and manures. The order was slightly changed to NH4H2PO4, KH2PO4, (NH4)2HPO4, chicken manure, and cattle manure with incorporation application under the same rainfall condition. Both the methods and the rate of manure application can affect the amounts of phosphorus in water and particles of runoff. More than 90 % of TP in runoff were lost through suspended particles. Manure application had a significant contribution to the P load in runoff.

Influence of Recent Acidification on Available Phosphorus Indices and Sorption in Washington State Soils

Gradual soil acidification in the Columbia Basin (CB), Washington State, brings into question the validity of the traditional sodium bicarbonate (NaHCO₃) extractable P (Olsen phosphorus, OP) method for making fertility recommendations. Our objectives were to determine how soil pH influences the soil P indices after fertilization and sorption capacity of soils with similar levels of available P at varying soil pH levels. Collected soils represented a range of pH (5.2–8.4) and OP (3–40 mg P kg⁻¹). Soils were treated with 0, 44, 88, or 132 kg P ha⁻¹ and incubated at 20°C for 6 wk. Subsamples were collected and analyzed for available P with OP, Bray P1 (BP1), modified Morgan (MMP), Mehlich-III (M3P) extractions. Additionally, P sorption isotherms were performed on untreated soils. Analysis of variance indicated that the slope of the change in extractable P was generally not significant (α = 0.05) for OP, BP1, MMP, and M3P given a P addition for several soils at different pH but of similar initial available P levels. Grouping soils by pH showed differences in slope with OP (0.27–0.34) yielding the least difference and MMP (0.12–0.33) the greatest related to soil pH. Langmuir parameters of b, sorption capacity, and k, binding energy, showed variability for soils grouped by initial available P for several pH levels. Grouped by pH there was little difference in P sorption in relation to soil pH. Continued use of OP on acidified soils of the CB appears to be a viable soil testing strategy.

The Effect of Nitrogen and Potassium Fertilizer on Yield and Mineral Accumulation in Flue-Cured Tobacco

In order to investigate the effect of nitrogen and potassium fertilizers on yield and mineral accumulation of cv.coker347 and cv.k326 of flue-cured tobacco, 2 year experiment was carried out in tobacco research institute of Rasht located in Guilan province on factorial based with 3 replications. The applied fertilizer levels included 35(N1), 45(N2), 55(N3) and 65 (N4) Kg/ha of pure nitrogen from urea source, and potassium in two levels of 150 (K1) and 200 (K2) Kg/ha potassium from potassium Sulfate. The measured parameters in this experiment included dried leaf weight, stem nitrogen, stem potassium, stem phosphorus, leaf nitrogen, leaf phosphorus, leaf potassium, plant nitrogen, plant phosphorus, plant potassium, nitrogen harvest Index, potassium harvest Index, phosphorus harvest Index. The effect of variety on dried leaf yield, stem nitrogen and plant potassium was significant on 1% level, and the variety had also significant effect on leaf potassium, plant nitrogen and nitrogen harvest Index on 5% level. The nitrogen had significant effect on parameters such as stem nitrogen, plant nitrogen on 1%level and similarly had significant effect on stem phosphorus, stem potassium and potassium harvest Index on 5% level. The potassium had significant effect on dried leaf, stem potassium on 1% level and also on plant potassium, potassium harvest Index on 5% level. The interaction between cultivar and nitrogen was significant on parameters like dried leaf yield, stem potassium, leaf nitrogen, plan nitrogen, plan potassium, nitrogen harvest Index and potassium harvest Index on 1% level and it was significant on stem nitrogen and leaf phosphorus on 5%level. The interaction between cultivar and potassium was significant on dried leaf, stem nitrogen, stem phosphorus, leaf nitrogen, leaf potassium, potassium harvest Index and nitrogen harvest Index on 1% level. This interaction on stem potassium was also significant on 5 % level. The interaction between nitrogen and potassium was significant on stem phosphorus, leaf potassium and potassium harvest Index on 1% level. This interaction on dried leaf yield, stem phosphorus, leaf nitrogen, and plant nitrogen and plant phosphorus was also significant on 5%level. The interaction among cultivar, nitrogen and potassium on parameters like dried leaf yield and stem phosphorus was significant on 1% level and this interaction on 5% level was also significant on plant potassium, leaf potassium and potassium harvest Index on 5% level