HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Berg, W. K. Articles by Volenec, J. J. Search for Related Content PubMed Articles by Berg, W. K. Articles by Volenec, J. J. Agricola Articles by Berg, W. K. Articles by Volenec, J. J. Related Collections Forage Management Alfalfa Plant Nutrition Soil Fertility and Productivity

FORAGE & GRAZINGLANDS

The Long-Term Impact of Phosphorus and Potassium Fertilization on Alfalfa Yield and Yield Components

Dep. of Agronomy, Purdue Univ., 915 West State St., West Lafayette, IN 47907-2054

^* Corresponding author (jvolenec{at}purdue.edu).

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Addition of P and K fertilizer can increase alfalfa (Medicago sativa L.) yield and stand persistence, but the yield components associated with P- and K-induced variation in agronomic performance are not clear. Our objectives were: (i) to determine the impact of P and K nutrition on productivity of a relatively old alfalfa stand; and (ii) determine which yield components are associated with changes in alfalfa forage yield. Treatments were a factorial combination of four P and five K rates replicated four times. Forage harvests occurred four times annually. Plant populations were determined in early December and late May each year. When compared to unfertilized plots, addition of P and K increased forage yield each year. Fertilization with P decreased plants m^–2 at all K application rates, but especially in plots fertilized with P, but not K. By comparison, plots fertilized with K, but not fertilized with P, had the higher plant population densities. Although regression analysis eventually revealed a positive association between forage yield and shoots m^–2 in 2003 and 2004, the greatest forage yields were not obtained in plots with the greatest plant population densities, shoots plant^–1 or shoots m^–2. Regression and path analysis revealed that improved forage yield in P- and K-fertilized plots was consistently associated with greater mass shoot^–1.

Abbreviations: ANOVA, analysis of variance

The Long-Term Impact of Phosphorus and Potassium Fertilization on Alfalfa Yield and Yield Components

Dep. of Agronomy, Purdue Univ., 915 West State St., West Lafayette, IN 47907-2054

^* Corresponding author (jvolenec{at}purdue.edu).

Addition of P and K fertilizer can increase alfalfa (Medicago sativa L.) yield and stand persistence, but the yield components associated with P- and K-induced variation in agronomic performance are not clear. Our objectives were: (i) to determine the impact of P and K nutrition on productivity of a relatively old alfalfa stand; and (ii) determine which yield components are associated with changes in alfalfa forage yield. Treatments were a factorial combination of four P and five K rates replicated four times. Forage harvests occurred four times annually. Plant populations were determined in early December and late May each year. When compared to unfertilized plots, addition of P and K increased forage yield each year. Fertilization with P decreased plants m^–2 at all K application rates, but especially in plots fertilized with P, but not K. By comparison, plots fertilized with K, but not fertilized with P, had the higher plant population densities. Although regression analysis eventually revealed a positive association between forage yield and shoots m^–2 in 2003 and 2004, the greatest forage yields were not obtained in plots with the greatest plant population densities, shoots plant^–1 or shoots m^–2. Regression and path analysis revealed that improved forage yield in P- and K-fertilized plots was consistently associated with greater mass shoot^–1.

Abbreviations: ANOVA, analysis of variance

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
THE IMPACT of P and K fertilization on alfalfa yield and persistence has been studied for many years (Nelson and MacGregor, 1957; Markus and Battle, 1965; Collins and Duke, 1981). A comprehensive understanding of the physiological and morphological basis for changes in alfalfa productivity in response to P and K fertilization remains elusive, however, because the components of yield are rarely analyzed, instead studies have tended to focus on cultivar x nutrient interactions (James et al., 1995). Other single-nutrient studies were conducted in controlled conditions that minimize many abiotic stresses (Li et al., 1997; 1998), or occurred in the field over a relatively short two or three year time periods (Collins and Duke, 1981; Collins et al., 1986). Recent studies have shifted focus to other questions such as P placement, and have shown occasional advantages to band application of P when compared to broadcast applications (Teutsch et al., 2000; Koenig et al., 2003). While these studies have been valuable in understanding several aspects of alfalfa P and K management, our knowledge of how alfalfa responds to P and K application remains rudimentary. This paper extends our earlier findings (Berg et al., 2005) on the impact of P and K fertilization on forage yield and yield component analysis during Years 1 to 3 (1998 to 2000) to learn how productivity and persistence change as an alfalfa stand ages between Years 4 to 7 (2001 to 2004).

Alfalfa plant populations are greatest immediately following establishment, and decline with time (Volenec, 1999). Adequate K nutrition is thought to enhance stand longevity (Wang et al., 1953; Smith, 1975). For example, Hanson and MacGregor (1966) reported that alfalfa stands receiving K fertilizer after first cutting, and both K and P fertilizer in autumn, maintained a denser stand after 10 years when compared to plots fertilized with only P. Surprisingly, there was no clear association between yield and stand density; however, plant counts were not reported in that study so the actual impact of P and K on alfalfa population densities is not known. However, Collins et al. (1986) counted crowns and reported that stand density in K-fertilized plots declined 50% between Years 1 and 2, whereas a 73% decline in plant density occurred in unfertilized control plots.

While fertilization with P often increases forage yield, conflicting results exist regarding the effects of P on alfalfa stand density. Jung and Smith (1959) reported that P fertilization was essential for plant survival. In contrast, Sanderson and Jones (1993) reported that P fertilization reduced alfalfa plant population densities. During their two year study, alfalfa populations declined from 495 to 98 plants m^–2 in plots provided 59 kg P ha^–1 annually, whereas unfertilized stands contained 134 plants m^–2 at the conclusion of the study. Collins et al. (1986) also reported decreased alfalfa populations in plots fertilized with P when compared to unfertilized control plots. Hanson and MacGregor (1966) reported that broadcast applications of K with P maintained more dense alfalfa stands than fertilization with P alone. Therefore, because P application may decrease alfalfa plant populations, the greater yield of P-fertilized plots should be reflected in increases in the other yield components of alfalfa (shoots plant^–1; mass shoot^–1).

Alfalfa yield has been positively associated with shoots area^–1. This yield component recently has been suggested as a criterion to determine whether or not to keep an existing alfalfa stand. Undersander et al. (1998) indicated that stem densities above 592 shoots m^–2 (55 shoots ft^–2) do not limit forage yield, however, some yield reduction is expected at shoot densities between 431 (40 shoots ft^–2) and 592 shoots m^–2. They recommend replacing the stand when shoot densities decline below 431 shoots m^–2. Using shoots plant^–1 and plant m^–2 data of Suzuki (1991), we estimated shoots m^–2 and observed the highest forage yields occurred at the lowest shoot densities (212 shoots m^–2).

Increased mass shoot^–1 has consistently been associated with improved agronomic performance of alfalfa irrespective of whether greater yields resulted from genetic selection (Volenec, 1985), improved soil fertility (Li et al., 1997, 1998), or better insect control (Kitchen et al., 1990). Cooper et al. (1967) attributed increased mass shoot^–1 with improved K fertility to an increased number of leaves per shoot. Others have associated high mass shoot^–1 with rapid shoot elongation rate after harvest (Volenec, 1985). During the initial three production years of the study reported here, mass shoot^–1 was consistently associated with increased forage yield (Berg et al., 2005). Plant population densities and shoots per area were unaffected by P and K fertility, or declined slightly even though yield was increased with P and K fertilizer application. However, interplant competition may have prevented fertility effects on shoot and plant densities from being detected during Years 1 to 3 (1998 to 2000). It is not known how alfalfa yield components interact to maintain high forage yield as plant populations naturally decrease with stand age, and how P and K fertilizer applications alter yield and yield components under these conditions.

Our hypothesis is that P and K fertilization is important to maintain high alfalfa yields, and because stands decline with age, yield will be influenced by different components than we found previously in a relatively young alfalfa stand (Berg et al., 2005). Our objectives were: (i) to determine the impact of P and K nutrition on productivity of a relatively old alfalfa stand, and (ii) determine which yield components are associated with changes in alfalfa forage yield.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Field Design and Sampling
In April 1997, a 1.4-ha site at the Throckmorton Purdue-Agricultural Center located 15 km south of West Lafayette, IN (40°N and 87°W) was seeded to Pioneer Brand ‘5454’ alfalfa. This site was selected for study because soil tests indicated low concentrations of extractable P (9 to 15 mg kg^–1 Bray P₁) and low to moderate levels of exchangeable K (108 to 138 mg kg^–1 exchangeable K) (Vitosh et al., 1996; Berg et al., 2005). Fertility treatments (0, 25, 50, and 75 kg P ha^–1; and 0, 100, 200, 300, and 400 kg K ha^–1) were applied to 5- x 10-m plots in a factorial design replicated four times. Two replications (field blocks) were placed on a Drummer silty clay loam (fine-silty, mixed superactive, mesic Typic Endoaquoll), while the other two replicates (field blocks) were placed on a Lauramie silt loam (fine-loamy, mixed, active, mesic, Mollic Hapludalf). Phosphorus (as triple super phosphate) and K (as potassium chloride) fertilizers were applied in split applications; with one half the annual amount broadcast after the first forage harvest in late May, and the remainder broadcast after the last forage harvest in mid-September. Chemical control of potato leafhoppers (Empoasca fabae Harris) and alfalfa weevil (Hypera postica Gyll.) was done as necessary using cyfluthrin [cyano(4-fluoro-3-phenoxyphenyl)methyl 3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropanecarboxylate)]. Plots were sprayed twice with sethoxydim [2-(1-ethoxyiminobutyl)-5-[2-(ethylthio)propyl]-3-hydroxycyclohex-2-enone] to reduce invasion of grasses. Monthly averages for maximum and minimum temperatures (air temperatures at 1.4 m above the soil surface; and bare soil temperatures at 0.1-m depth below the soil surface) and precipitation from January 2001 through December 2004 were obtained at the Agronomy Center for Research and Education located 15 km north of the experimental site (Table 1 ).

Statistical Analysis
Analysis of variance was performed on the yield components, and the P, K, and P x K treatment effects were partitioned into orthogonal polynomial contrasts as previously described (Berg et al., 2005). In this analysis the ORPOL function in PROC IML of SAS was used to obtain orthogonal polynomial coefficients. These values were assigned to dummy variables representing linear, quadratic, cubic, and quartic polynomial contrasts and their interactions. The REG procedure was run with these dummy variables as independent variables; where the Type II sums of squares are the sums of squares for the corresponding contrasts. Regression models incorporating terms for all significant polynomial contrasts were developed and evaluated on treatment means. Occasionally a regression model exhibiting an anomalous relationship was rejected. Differences in equation slopes were determined using the standard error of the difference between the slopes adjusted for the experimental error. Because forage yield is a linear function of mass shoot^–1 and shoots m^–2 (and at May harvests mass shoot^–1, shoots plant^–1, and plants m^–2), and given that yield components themselves are often correlated with one another, we used path analysis (also known as analysis of correlation, Li, 1956) to determine the direct effects of individual yield components on forage yield. The ratio of path coefficients of the yield components at a particular harvest provides an estimate of the relative influence of each yield component on forage yield at that harvest. Statistical analyses were performed using SAS (SAS, 1999).

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Forage Yield
When compared to the unfertilized control plots, application of P and K resulted in greater forage yield each year of this study (Fig. 1 ). Maximum forage yields were lower in 2003 when compared to the other years, possibly due to the lower soil temperatures in June and July of that year (Table 1). Evenson (1979) showed a linear reduction in herbage growth as crown temperatures declined below 30°C. Between 2001 (fourth year of production) and 2004 (seventh year of production), the impact of adequate P and K fertilization on forage yield became progressively more evident. In 2001 there was a 33% difference between the highest and lowest forage yield, but by 2004 this difference had increased to 300% (Fig. 1). These large changes in yield provide an excellent opportunity to quantify the impact of P and K fertility on yield and yield components of alfalfa.

View larger version (23K): [in this window] [in a new window]   Figure 1. Influence of P and K fertilizer application on annual forage yield (kg ha–1 yr–1) in 2001 to 2004. Contour plots are generated from the regression equations listed in Table 3 for total yield.

Yield Components
Plant Population Density
Alfalfa forage yield can be described as the product of three components: plants area^–1, shoots plant^–1, and mass shoot^–1 (Volenec et al., 1987). Ignoring the influence of P and K, plots averaged 130 plants m^–2 in May 2001, and this decreased to 46.7 plants m^–2 by May 2004 (Table 3 ; intercepts of regressions). Analysis of variance indicated significant linear effects of K on plants m^–2 in five of eight samplings (Table 4 ). Where K effects were significant, plants m^–2 increased with K fertilization (Table 3). Analysis of variance revealed significant linear and quadratic effects of P on plants m^–2 at six of eight samplings between May 2001 and December 2004 (Table 4). Where significant, application of P reduced plants m^–2 (Table 3). At the highest rates of P (75 kg ha^–1) and K (400 kg ha^–1) the regressions in Table 3 predicted an increase of 17 plants m^–2 due to K fertilization, and a reduction of 27 plants m^–2 due to P averaged across the five of eight harvests where both P and K significantly influenced plants m^–2.

Adequate K nutrition has often been positively associated with improved alfalfa persistence (Gerwig and Ahlgren, 1958; Burmester et al., 1991; Simons et al., 1995). However, K fertilizer application enhanced plant populations in only five of eight samplings, where on average, the 400 kg K ha^–1 yr^–1 treatment increased populations by 28% (Table 3; calculated using regression equations). By comparison, P fertilization reduced plant populations in six of eight samplings by an average of 48% at the 75 kg P ha^–1 fertilizer rate (Table 3). The decrease in alfalfa populations observed in response to enhanced P fertilization agrees with trends previously reported (Sanderson and Jones, 1993; Berg et al., 2005). In a decade-long alfalfa fertility study, Hanson and MacGregor (1966) reported that stand densities in plots fertilized with both P and K were greater than stand densities of plots fertilized with P alone. In addition, they reported no association between variation in stand density (37 to 62% of stand) and forage yield. We found that the highest rates of P and K fertilization resulted in the greatest forage yields in 2004 (Fig. 1), and these occurred at intermediate plant populations of approximately 40 plants m^–2 (Fig. 2 ). Although 50% higher plant populations occurred when plots were fertilized with K but not P (Fig. 2), the relatively small size of these P-limited plants resulted in lower forage yield (Fig. 1).

View larger version (27K): [in this window] [in a new window]   Figure 2. Influence of P and K fertilizer application on shoots plant–1, shoots m–2, plants m–2, and mass shoot–1 at Harvest 1 in May 2004. The contour plots were generated from the regression equations listed in Table 3 for Harvest 1 of 2004.

These results agree with those of Lemaire et al. (1991) who suggested that competition for light within an alfalfa stand decreased plant populations in a manner consistent with the –3/2 thinning law. Preferential death of the smallest plants in the population occurred because of extensive shading and low plant N content. Kays and Harper (1974) interpreted changes in slope of the log(plant size) versus log(plant density) regression to values greater than –1.5 (i.e., –1.0) as an indication that the stress factor (in our case, K and P deficiency) has a causal role in stand thinning in addition to interplant competition per se. This highlights the importance of adequate K and P nutrition in enabling increases in plant size to offset reductions in plant population that are essential for maintaining high forage yield as alfalfa stand density declines.

Shoots Plant^–1
Taproots were excavated and counted only at Harvest 1, therefore, shoots plant^–1 can only be calculated at this harvest of each year. Shoots plant^–1 was not influenced by P or K fertilization in 2001, 2002, or 2003; however, in 2004 significant orthogonal polynomial contrasts were obtained. The ANOVA (analysis of variance) of shoots plant^–1 in 2004 revealed that while P fertilization increased shoots plant^–1, K fertilization reduced shoots plant^–1 at most P rates (Fig. 2). For example, plants provided 75 kg ha^–1 P had 14 shoots plant^–1 when fertilized with 0 kg K ha^–1 yr^–1, but shoots plant^–1 declined to between six and eight shoots plant^–1 when plants were fertilized with 75 kg ha^–1 P and 300 or 400 kg K ha^–1 yr^–1. The highest shoots plant^–1 values (14 shoots plant^–1) occurred in plots with the fewest plants m^–2 (20 plants m^–2) (Fig. 2). This agrees with previous results where genetic differences in shoots plant^–1 were only evident when plant populations declined to 22 or fewer plants m^–2 (Volenec et al., 1987).

While shoots are clearly needed for forage yield, high forage yield was not closely associated with greater shoots plant^–1. For example, in 2004, the greatest yield was produced in plots provided 400 kg K ha^–1 yr^–1 and 75 kg P ha^–1 yr^–1 (Fig. 1) that had 7 or 8 shoots plant^–1 (Fig. 2), whereas plots fertilized with 75 kg P ha^–1 yr^–1 and no K fertilizer had the highest number of shoots plant^–1, but the lowest forage yield in 2004 because of high plant mortality. During the initial three production years of this study (1998 to 2000), slight increases in shoots plant^–1 occurred as plant populations decreased, but these changes were independent of P and K fertilization (Berg et al., 2005). These findings also have implications for alfalfa improvement strategies because genetic enhancement of shoots plant^–1 is unlikely to result in higher yielding alfalfa because genetic differences in shoots plant^–1 are not evident under competitive conditions found in most stands (Volenec et al., 1987)

Shoots m^–2
The ANOVA revealed an occasionally significant K x P orthogonal polynomial contrast (Table 6 ). Potassium had a significant positive influence on shoots m^–2 in 11 of 16 harvests, no significant impact on two of 16 harvests, and a significant negative effect in three of 16 harvests (Table 3). Using regression equations in Table 3, the positive response to 400 kg ha^–1 yr^–1 K fertilization rate ranged from a low of 19 shoots m^–2 (Harvest 2 of 2001) to a high of 182 shoots m^–2 (Harvest 3 of 2004), with an average positive response of 94 shoots m^–2. At the 400 kg K ha^–1 yr^–1 rate the three negative responses of shoots m^–2 to K fertilizer application ranged from a reduction of 90 shoots m^–2 (Harvest 1 of 2001) to a reduction of 152 shoots m^–2 (Harvest 4 of 2002), with an average reduction of 112 shoots m^–2.

Regression analysis of shoots m^–2 versus forage yield revealed significant linear relationships between these two traits at 14 of 16 harvests (Table 7 ). The r²-values ranged from 0.00 (Harvest 1 of 2002) to 0.94 (Harvest 2 of 2003). Although the r²-values were relatively low, the negative slopes obtained in three of four harvests in 2001 indicate that increases in shoots m^–2 reduced forage yield at these harvests. Harvests 2 and 3 in 2002, and all harvests in 2003 and 2004 exhibited a positive relationship between shoots m^–2 and forage yield indicating that increasing shoots m^–2 at these harvests would have a positive impact on forage yield. The negative relationship between forage yield and shoots m^–2 that was observed at three of four harvests in 2001 confirms a pattern also observed during 1998 to 2000 where fertility-driven increases in forage yield coincided with reductions in shoots m^–2 (Berg et al., 2005). Although a positive relationship between shoots m^–2 and yield also was evident at every harvest in 2003 and 2004, the greatest forage yields were never obtained in plots with the highest shoot densities. For example, in May 2004 shoot densities ranged from 200 shoots m^–2 in plots provided 75 kg P ha^–1 yr^–1 and no K to 340 shoots m^–2 in plots fertilized with 300 or 400 kg K ha^–1 yr^–1 without P (Fig. 2). The highest forage yield was obtained at shoot densities of approximately 260 shoots m^–2 that occurred when high rates of both P and K were provided (Fig. 1). Despite this inconsistency, alfalfa yield potential is often predicted using shoots area^–1 with significant losses in forage yield anticipated when shoot density declines below the "benchmark" value of 430 shoots m^–2 (40 shoots ft^–2) (Undersander et al., 1998). The high forage yields obtained in May of 2004 occurred at shoot densities far below this benchmark value (Fig. 2). Additional research is needed to accurately define critical shoot densities for high yielding alfalfa and how this value varies with P and K fertility, harvest, and stand age.

Mass shoot^–1 was consistently positively associated with forage yield at every harvest in each year (Table 7). Like forage yield, mass shoot^–1 consistently responded to P and K fertilization, including significant interactions for P and K at nearly every harvest each year (Table 8). Subsequent analysis of all 28 harvests obtained in this seven year study revealed no evidence for a decline in the response of yield to increased mass shoot^–1 across the range in values (0.2–3.0 g shoot^–1) (Volenec et al., 2005). Previous research demonstrated genetic variation in mass shoot^–1 and showed that this trait was negatively correlated with genotypic differences in shoots plant^–1 (Volenec et al., 1987). Additional research is needed to understand the genetic constraints on mass shoot^–1 and determine if the negative correlation between shoots plant^–1 and mass shoot^–1 observed in this study will serve as an impediment to alfalfa yield improvement using yield component strategies.

Both mass shoot^–1 and shoots m^–2 were positively associated with forage yield at some harvests (Table 7). However, these two yield components are often negatively correlated to one another, which confounds the interpretation of correlation analysis. These two yield components also are mathematically related because we calculate shoot population densities based on forage yield and shoot mass measurements. To better understand the direct effect of each yield component on forage yield, two-way path analysis (shoots m^–2 and mass shoot^–1) was performed at all harvests, and three-way path analysis (plants m^–2, shoots plant^–1, and mass shoot^–1) was performed using data from Harvest 1 of each year where we had plants m^–2 information. Plant breeders have used path analysis to understand the relative importance of yield components of grain crops to grain yield. The common approach is to calculate the ratio of the path coefficients because this ratio estimates the relative contributions of individual yield components to yield at that harvest (Li, 1956; Dofing and Knight, 1992; Gravois and Helms, 1992).

Two-way path analysis revealed that mass shoot^–1 generally made a greater contribution to forage yield in this study than did shoots m^–2. At 13 of 16 forage harvests the ratio of path coefficients, mass shoot^–1:shoots m^–2, exceeded 1 indicating a greater relative direct effect of mass shoot^–1 on forage yield (Table 9 ). At Harvests 3 and 4 of 2004 the ratio of these path coefficients was approximately equal to 1 indicating that these two yield components were of equal relative importance in determining forage yield near the end of the study. Only at Harvest 2 of 2003 was shoots m^–2 of greater importance than mass shoot^–1 in determining forage yield of this alfalfa stand. At Harvest 1 of each year the ratio of path coefficients was 2.2 or greater indicating that at this harvest, mass shoot^–1 was at least twice as important as shoots m^–2 in directly affecting forage yield.

Both regression and path analysis revealed that mass shoot^–1 of alfalfa was consistently related to improved forage yield in response to P and K fertilization. This conclusion agrees with our observations from 1998 to 2000 (the first three production years of this stand) when mass shoot^–1 also was consistently associated with forage yield (Berg et al., 2005). Factors that increase mass shoot^–1 including genetics, environment, and management are likely to result in higher forage yield of alfalfa. From a plant development perspective, increased mass shoot^–1 results from two plausible mechanisms: rapid initiation of new shoots from crowns after forage harvest; and high shoot elongation rates following initiation of growth (Singh and Winch, 1974; Li et al., 1997). We have previously shown that genetic variation in shoot elongation rate exists in alfalfa, and that those cultivars and germplasms with high shoot elongation rates had greater mass shoot^–1 and high forage yields (Volenec, 1985).

We also observed that as stands aged increasing rates of P, and especially K were required to maintain high forage yield. Current work is focusing on how soil test P and K concentrations changed between 1998 and 2004, and how this influenced tissue P and K concentrations and the decline in agronomic performance of alfalfa over time. Additional studies are underway to understand the impact of long-term P and K fertilization on alfalfa forage quality (Lissbrant et al., 2006a). Preliminary results indicate that concentrations of neutral detergent fiber, acid detergent fiber, and lignin are slightly lower, and crude protein concentrations higher in forage of P- and K-deficient alfalfa plants. In addition, we are using cluster analysis to better understand how P and K fertilization influence alfalfa yield and persistence over time (Lissbrant et al., 2006b), and what role organic reserves in alfalfa taproots have in alfalfa yield and persistence to develop diagnostic tools to better predict long-tem alfalfa performance.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.

Received for publication September 13, 2006.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 

• Berg, W.K., S.M. Cunningham, S.M. Brouder, B.C. Joern, K.D. Johnson, and J.J. Volenec. 2005. Influence of phosphorus and potassium fertilization on alfalfa yield and yield components. Crop Sci. 45:297–304.[Abstract/Free Full Text]
• Burmester, C.H., G.L. Mullins, and D.M. Ball. 1991. Potassium fertilizer effects on the yield and longevity of established alfalfa. Comm. Soil Plant Anal. 2:2047–2062.
• Collins, M., and S.H. Duke. 1981. Influence of potassium-fertilizer rate and form on photosynthesis and N₂ fixation of alfalfa. Crop Sci. 21:481–485.[Abstract/Free Full Text]
• Collins, M., D.J. Lang, and K.A. Kelling. 1986. Effects of phosphorus, potassium and sulfur on alfalfa nitrogen-fixation under field conditions. Agron. J. 78:959–963.[Abstract/Free Full Text]
• Cooper, R.B., R.E. Blaser, and R.H. Brown. 1967. Potassium nutrition effects on net photosynthesis and morphology of alfalfa. Soil Sci. Soc. Am. Proc. 31:231–234.
• Dofing, S.M., and C.W. Knight. 1992. Alternative model for path analysis of small-grain yield. Crop Sci. 32:487–489.[Abstract/Free Full Text]
• Evenson, P.D. 1979. Optimum crown temperatures for maximum alfalfa growth. Agron. J. 71:798–800.[Abstract/Free Full Text]
• Frakes, R.V., R.L. Davis, and F.L. Patterson. 1961. The breeding behavior of yield and related variables in alfalfa. II. Associations between characters. Crop Sci. 1:207–209.[Free Full Text]
• Gravois, K.A., and R.S. Helms. 1992. Path analysis of rice yield and yield components as affected by seeding rate. Agron. J. 84:1–4.[Abstract/Free Full Text]
• Gerwig, J.L., and G.H. Ahlgren. 1958. The effect of different fertility levels on yield, persistence, and chemical composition of alfalfa. Agron. J. 50:291–294.[Abstract/Free Full Text]
• Hanson, R.G., and J.M. MacGregor. 1966. Soil and alfalfa plant characteristics as affected by a decade of fertilization. Agron. J. 58:3–5.[Abstract/Free Full Text]
• James, D.W., T.A. Tindall, C.J. Hurst, and A.N. Hussein. 1995. Alfalfa cultivar responses to phosphorus and potassium deficiency. Biomass. J. Plant Nutr. 18:2431–2445.[Web of Science]
• Jung, G.A., and D. Smith. 1959. Influence of soil potassium and phosphorus content on the cold resistance of alfalfa. Agron. J. 51:585–587.[Abstract/Free Full Text]
• Kays, S., and J.L. Harper. 1974. The regulation of plant and tiller density in a grass sward. J. Ecol. 62:97–105.[CrossRef]
• Koenig, R., K. Heaton, J. Barnhill, and C. Reid. 2003. Phosphorus and sulfur sources and placements for irrigated alfalfa. West. Nutr. Mgmt. Conf. 5:124–130.
• Kitchen, N.R., D.D. Buchholz, and C.J. Nelson. 1990. Potassium fertilizer and potato leafhopper effects on alfalfa growth. Agron. J. 82:1069–1074.[Abstract/Free Full Text]
• Lemaire, G., B. Onillon, G. Gosse, M. Chartier, and J.M. Allirand. 1991. Nitrogen distribution within a lucerne canopy during regrowth: Relation to light distribution. Ann. Bot. (Lond.) 68:483–488.[Abstract/Free Full Text]
• Li, C.C. 1956. The concept of path coefficient and its impact on population genetics. Biometrics 12:190–210.[CrossRef][Web of Science]
• Li, R., J.J. Volenec, B.C. Joern, and S.M. Cunningham. 1997. Potassium and nitrogen effects on carbohydrate and protein metabolism in alfalfa roots. J. Plant Nutr. 20:511–529.[Web of Science]
• Li, R., J.J. Volenec, B.C. Joern, and S.M. Cunningham. 1998. Effects of phosphorus nutrition on carbohydrate and protein metabolism in alfalfa roots. J. Plant Nutr. 21:459–474.[Web of Science]
• Lissbrant, S., S. Stratton, S.M. Cunningham, and J.J. Volenec. 2006a. Impact of long-term P and K fertilization on alfalfa forage quality. ASA-CSSA-SSSA Inter. Ann. Meetings, Indianapolis IN. Oral presentation 72–2.
• Lissbrant, S., S.M. Brouder, B.C. Joern, S.M. Cunningham, and J.J. Volenec. 2006b. Cluster analysis as a tool for identification of fertility regimes that enhance long-term productivity of alfalfa. ASA-CSSA-SSSA Inter. Ann. Meetings, Indianapolis IN. Poster 315. http://crops.confex.com/crops/2006am/techprogram/P24638.HTM (verified 14 August 2007).
• Markus, D.K., and W.R. Battle. 1965. Soil and plant responses to long-term fertilization of alfalfa (Medicago sativa L.). Agron. J. 57:613–616.[Abstract/Free Full Text]
• Nelson, W.W., and J.M. MacGregor. 1957. The effect of time and rate of fertilizer application on the yield, composition, and longevity of alfalfa. Soil Sci. Soc. Am. Proc. 21:42–46.
• Sanderson, M.A., and R.M. Jones. 1993. Stand dynamics and yield components of alfalfa as affected by phosphorus fertility. Agron. J. 85:241–246.[Abstract/Free Full Text]
• SAS. 1999. SAS/STAT User's Guide. Version 8. SAS Institute Inc, Cary, NC.
• Simons, R.G., C.A. Grant, and L.D. Bailey. 1995. Effects of fertilizer placement on yield of established alfalfa stands. Can. J. Plant Sci. 75:883–887.
• Singh, Y., and J.E. Winch. 1974. Morphological development of two cultivars under various harvesting schedules. Can. J. Plant Sci. 54:79–87.
• Smith, D. 1975. Effects of potassium topdressing a low fertility silt loam soil on alfalfa herbage yields and composition and on soil K values. Agron. J. 67:60–64.[Abstract/Free Full Text]
• Suzuki, M. 1991. Effects of stand age on agronomic, morphological, and chemical characteristics of alfalfa. Can. J. Plant Sci. 71:445–452.
• Teutsch, C.D., R.M. Sulc, and A.L. Barta. 2000. Banded phosphorus effects on alfalfa seedling growth and productivity after temporary waterlogging. Agron. J. 92:48–54.[Abstract/Free Full Text]
• Undersander, D.J., C. Grau, D. Cosgrove, J. Doll, and N. Martin. 1998. Alfalfa stand assessment: Is the stand good enough to keep? Ext. Bull. A3620. Univ. of Wisconsin, Madison, WI.
• Vitosh, M.L., J.W. Johnson, and D.B. Mengel. 1996. Tri-state fertilizer recommendations. Ext. Bull. E-2567. Michigan State University, East Lansing, MI.
• Volenec, J.J. 1985. Leaf area expansion and shoot elongation of diverse alfalfa germplasms. Crop Sci. 25:822–827.[Abstract/Free Full Text]
• Volenec, J.J. 1999. Physiological control of alfalfa yield and growth. p. 425–442. In D.L. Smith and C. Hamel (ed.) Physiological control of growth and yield in field crops. Springer-Verlag, New York.
• Volenec, J.J., J.H. Cherney, and K.D. Johnson. 1987. Yield components, plant morphology, and forage quality of alfalfa as influenced by plant population. Crop Sci. 27:321–326.[Abstract/Free Full Text]
• Volenec, J.J., W.K. Berg, S.M. Cunningham, S.M. Brouder, and B.C. Joern. 2005. Critical shoot density and forage yield of alfalfa. ASA-CSSA-SSSA Inter. Ann. Meetings, Salt Lake City, UT. Abstr. No. 67–5, CD-ROM.
• Wang, L.C., O.J. Attoe, and E. Truog. 1953. Effect of lime and fertility level on the chemical composition and winter survival of alfalfa. Agron. J. 45:381–384.[Free Full Text]
• Yoda, K., T. Kira, H. Ogawa, and K. Hozumi. 1963. Intraspecific competition among higher plants. XI. Self-thinning in overcrowded pure stands under cultivated and natural conditions. J. Biol. 14:107–129.

This article has been cited by other articles:

				W. K. Berg, S. M. Cunningham, S. M. Brouder, B. C. Joern, K. D. Johnson, and J. J. Volenec Influence of Phosphorus and Potassium on Alfalfa Yield, Taproot C and N Pools, and Transcript Levels of Key Genes after Defoliation Crop Sci., May 11, 2009; 49(3): 974 - 982. [Abstract] [Full Text] [PDF]

				S. Lissbrant, S. Stratton, S. M. Cunningham, S. M. Brouder, and J. J. Volenec Impact of Long-Term Phosphorus and Potassium Fertilization on Alfalfa Nutritive Value-Yield Relationships Crop Sci., May 11, 2009; 49(3): 1116 - 1124. [Abstract] [Full Text] [PDF]

				R. Koenig, D. Winward, C. Reid, J. Barnhill, M. Pace, and K. Heaton Phosphorus Source and Surface Fluid Band Spacing Effects on Irrigated Alfalfa Soil Sci. Soc. Am. J., February 6, 2009; 73(2): 367 - 374. [Abstract] [Full Text] [PDF]

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Berg, W. K. Articles by Volenec, J. J. Search for Related Content PubMed Articles by Berg, W. K. Articles by Volenec, J. J. Agricola Articles by Berg, W. K. Articles by Volenec, J. J. Related Collections Forage Management Alfalfa Plant Nutrition Soil Fertility and Productivity