Leaching-losses of nitrogen from pot chrysanthemums with controlled-release or liquid fertilization

Scientia Horticulturae, 17 (1982) 145--152

145

Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

LEACHING-LOSSES OF NITROGEN FROM POT CHRYSANTHEMUMS WITH CONTROLLED-RELEASE OR LIQUID FERTILIZATION

DAVID R. HERSHEY and J.L. PAUL

Department of Environmental Horticulture, University of California, Davis, CA 95616 (U.S.A.) (Accepted for publication 7 August 1981)

ABSTRACT Hershey, D.R. and Paul, J.L., 1982. Leaching-losses of nitrogen from pot chrysanthemums with controlled-release or liquid fertilization. Scientia Hortic., 17: 145--152. Leaching-losses of N from pot chrysanthemums fertilized with either "Osmocote", a controlled-release fertilizer (CRF), or a continuous liquid feed (LF) were measured during an l l - w e e k crop cycle. The leaching-fraction averaged 27% for both CRF and LF treatments. The N lost through leaching was greater at higher rates of both CRF and LF. With CRF, most of the N loss occurred during the first half of the crop cycle, while with LF, leaching-losses of N occurred throughout the experiment. The percentage of the applied N lost by leaching varied from 12 to 23% with CRF at rates of 1.68--3.36 g N/pot, while losses with LF ranged from 12 to 48% with levels of 1.2--3.6 g N/pot. The leaching-losses for CRF expressed as the percentage of the N released during the crop cycle ranged from 15 to 29%.

INTRODUCTION

Controlled-release fertilizers are used for many container crops (Maynard and Lorenz, 1979), although application of soluble fertilizer in the irrigation water (liquid feeding) is still the most c o m m o n method of fertilization (Bunt, 1976; Seeley and Langhans, 1977). Liquid feeding is considered to be fairly inefficient when surface irrigation is used because of the large leaching-losses of nutrients (Furuta, 1976; Bunt, 1976; Barron, 1977; Holcomb, 1980). A widely claimed advantage of controlled-release fertilizer (CRF) over liquid feed (LF) is the reduction of nutrient loss via leaching, resulting in higher efficiency of nutrient recovery and reduced fertilizer run-off (Furuta, 1976; Barron, 1977; Holcomb, 1979; Maynard and Lorenz, 1979; Sharma, 1979; Oertli, 1980). The efficiency of N recovery, defined as the percentage of applied N absorbed by the plant, was estimated at 16% by Barton (1977) and at 46% by Holcomb (1979) for a crop of pot chrysanthemums receiving a liquid feed containing 200 mg N/1. For "Osmocote", a controlled-release fertilizer, the efficiency was calculated at 89% by Holcomb (1979), while Barron 0304-4238/82/0000--0000/$02.75 O 1982 Elsevier Scientific Publishing Company

146

(1977) also stated that much higher efficiencies were achievable with Osmocote. In their calculations, Holcomb (1979) and Barton (1977) suggest that the differences in N fertilizer efficiencies between CRF and LF result from differences in the N-leaching losses between the two. Thus, in the above example, leaching losses of applied N would be 54% for LF and only 11% for Osmocote (Holcomb, 1979). Such estimates of N fertilizer efficiency and leaching-losses appear plausible. However, there are few published results for container crops with which to compare these calculations. The purpose of the present study, therefore, was to determine the leaching-losses of N by a crop of pot chrysanthemums receiving either controlled-release fertilizer or liquid feed. MATERIALS AND METHODS

The potting-medium was sphagnum peat moss with the following fertilizers and chemical amendments incorporated per 1.5-liter potful: 6 g dolomite; 3 g CaCO3; 2 g single superphosphate (0--20--0); 0.3 g K2SO4; 3.44 g K-frit (0--0--35); 1.5 g "Micromax" micronutrient fertilizer, containing 12% Fe, 2.5% Mn, 1% Zn, 0.5% Cu, 0.1% B, 0.005% Mo, and 15% S. There were 3 CRF nitrogen application rates and 3 LF nitrogen application rates, each with 5 replications (1 pot/replication). The CRF, Osmocote (14-14--14), having a 3- to 4-month release time, was surface-applied at 12, 18 and 24 g/pot. The rates were 1, 1.5 and 2 times the manufacturer's recommended rate and corresponded to 1.68, 2.52 and 3.36 g N/pot, respectively. We choose the standard rate of Osmocote as the lowest level, based on results from an earlier experiment performed in this lab and those of 8harma and Patel (1978), in which a higher than standard rate of Osmocote was required to produce yields equivalent to a LF with 200 mg N/1. The CRF treatments were irrigated with a solution containing the following ions in meq per liter: 3 Ca2+; 2 Mg2+; 1 Na÷; 1 C1-; 5 SO~-. The 3 LF treatments were irrigated with 3 nutrient solutions (Table I), which were prepared with the same solution used to irrigate the 3 CRF treatments. The total amounts of N applied with LF were 1.21, 2.24 and 3.57 g N/pot for the 98,196 and 294 mg N/1 treatments, respectively. TABLE I Nutrient solution formulations used in the liquid feed (LF) treatments N concentration (mg/l)

98 196 294

Concentration (meq/1)

Ca(NO3)2

NH4NO3

KNO3

NH4H2PO4

0 4.5 9.5

0.25 1.5 2.5

6.0 6.0 6.0

0.5 0.5 0.5

147

R o o t e d cuttings of Chrysanthemum X morifolium Ramat. 'Bright Golden Anne' were planted 4 per 15-cm plastic p o t on 1 November 1980. The pots were initially spaced 23 X 23 cm on raised benches in a glasshouse with minimum temperatures of 20°C (day) and 16°C (night), and maintained under long days (incandescent light from 10 p.m. to 2 a.m.) for one week after planting. On 7 November, the plants were given a soft pinch and shortday conditions were imposed. Pots were irrigated every other day and leached weekly. The leachates were collected, weighed to estimate volume, and analyzed for NO3-N and NH4-N using the m e t h o d of Carlson (1978). The average volume of leachate collected was 350 ml, and the overall leaching-fraction (volume leached/volume applied X 100) was between 25 and 30% (see Table II). Pots were spaced to 35 X 35 cm on 4 December and the plants were disbudded to leave one flower per stem, with an average of 11 flowers per pot. All plants were harvested on 17 January 1981, when the flowers were a b o u t half-open. Fresh weight of plant tops was measured as an index of yield. After harvest, the Osmocote granules were collected from several pots and analyzed for N to determine the amount of N that had been released during the crop cycle. RESULTS AND DISCUSSION

The total volume of solution applied (about 12.5 1/pot) was quite similar for all treatments (Table II) and was nearly half the amount applied during the spring or summer months in our glasshouse. The total volume of solution leached per p o t was also similar among the treatments, which resulted in an T A B L E II V o l u m e o f s o l u t i o n applied a n d l e a c h e d , l e a c h i n g - f r a c t i o n , a n d fresh w e i g h t yields o f c h r y s a n t h e m u m s for liquid f e e d a n d O s m o c o t e t r e a t m e n t s . N u m b e r s r e p r e s e n t t r e a t m e n t averages a n d s t a n d a r d d e v i a t i o n s Treatment

Volume applied (1/pot)

Volume leached (l/pot)

Leachingfraction (%)

Fresh weight tops (g/pot)

" O s m o c o t e " ( 1 4 - - 1 4 - - 1 4 ) 3--4 m o n t h release (g/pot) 12 18 24

12.74 +- 0.42 1 2 . 7 3 -+ 0.06 1 2 . 7 6 -+ 0.16

3.27 +- 0.28 3.40 +- 0.15 3.53 -+ 0.22

25.8 ± 2.7 26.8 +- 1.3 27.6 -+ 2.0

241.5 254.9 253.5

12.37 -+ 0.15 1 2 . 3 7 -+ 0.30 1 2 . 1 3 +- 0.06

3.29 +- 0.33 3.51 + 0.27 3.59 -+ 0.08

26.6 + 2.9 28.2 -+ 2.7 29.8 + 0.7

255.0 260.6 241.2

Nutrient solution (mg N/I) 98 196 294

148

average leaching-fraction that varied from 26 to 30% (Table II). The average leaching-fraction obtained was similar to that often encountered under commercial growing-conditions. Fresh weight yields (Table II) were not significantly different among the 6 treatments, although there was a slight delay in flowering, of up to 7 days, in the Osmocote treatments. The lack of plant response to increasing N application rates probably occurred because of the low light levels during the season when the crop was grown. Apparently light, not N, was the factor limiting growth. Chrysanthemum yields in this study were lower than in our earlier experiment and in the experiment reported by Sharma and Patel (1978), and were due, in part, to the shorter period of vegetative growth and to the lower light levels in our glasshouse. N concentrations in leachates. - - I n Fig. 1, the N concentration in the leachate

at every leaching (weekly) is shown as a function of time after planting. The N concentration of the leachate displaced from the pot is probably very Osmocote

600! o o

400

[] [3

2OO ._

[]

o

\

o 0

E

o

0

O

0

Liquid feed

u

o

0

0

_e 6 0 0 c

z

o

o

[]

400 0

[] [] []

200 o []

'

o

0 []

[]

[]

~

;

T

4

:

" •

;

s

,

,'o

Weeks after planting

Fig. 1. Nitrogen concentration in leachates with time for pot chrysanthemums receiving the CRF Osmocote (14--14--14), at 1.68 (e), 2.52 (a) and 3.36 (o) g N/pot and liquid feed at concentrations of 98 (e), 196 (D) and 294 (o) mg N/1.

149

similar to that of the soil solution just before leaching, although there is u n d o u b t e d l y some mixing of the soil solution and applied solution during the leaching-process. If the N concentration in the leachate is greater than that in the applied solution (2 highest LF treatments and all Osmocote treatments), then this represents the maximum N concentration to which the roots were exposed between leachings, since following leaching, the remaining soil solution is diluted b y the applied solution. Conversely, if the concentration of N in the leachates is less than that in the applied solution, as in the 98 mg N/1 treatment, then the N concentration in the leachate represents the minimum N concentration to which the roots were exposed between leachings. Leaching-losses o f N with CRF. -- Ideally, the nutrient release pattern of a

CRF should coincide with the uptake pattern of the crop (Barton, 1977; Oertli, 1980). However, in our experiment the high concentration of N in the leachates of the CRF treatments during the first few weeks (see Fig. 1) indicated that the rate of N release during this period was much greater than the rate of N uptake by the plants. This poor correlation between N release from Osmocote and N uptake b y chrysanthemums during the early part of the crop cycle clearly resulted in substantial leaching-losses (Fig. 2). If the N release rate of Osmocote (14--14--14) is almost constant for the first 3 months, as the manufacturer suggests, then the decline in the concentration of N in the leachates with time (see Fig. 1) could have been due, in large part, to the increase in the rate of N uptake by the plants (Kofranek and Lunt, 1966; Bunt, 1976, p. 69). An alternate explanation is that the N release-rate of Osmocote decreased during the first half of the crop cycle. During the last half of the crop cycle, the uptake rate nearly equalled the N releaserate, and the N concentrations in the leachates were very low and leachinglosses were negligible. The efficiency of N recovery with Osmocote was, therefore, very low during the early part of the crop cycle, b u t increased to nearly 100% during the final 4 weeks. This is in agreement with the results of Leung (1970). The N in the leachates of the CRF treatment was present as approximately half NO~ and half NH~. The high proportion of NH~ in the leachates was due to the high NH~ content of Osmocote (58.6% of N as NH~ and 41.4% as NO~) and suggests that little nitrification occurred. Leaching-losses o f N with LF. -- For the LF treatments, 11 or 14% of the N

was applied as NH~, yet the NH~ level in the leachates accounted for less than 1% of the N concentration, except for the first week when 7% of the N in the leachate was present as NH~. Virtually all of the N in the leachates of the LF treatments, therefore, was in the NO~ form. At the 2 highest levels of LF, the profile of N concentration in the leachates with time was the reverse of that for the CRF treatments; N concentrations in the leachates were relatively low the first week, b u t increased until the sixth week when they appeared to level off at 300 and 600 mg N/1 (see Fig. 1). With LF at 98 mg N/l, the N concen-

150

Osmocote

0.8

o

0

0

0

[]

[]

0

[]

[]

•

•

o 0 0

0.4

0

[]

o 0

o

[]

o

•

•

0 Q.

1.6

Liquid feed

'0 .(= o

0

z

1.2

0.8

[] o

[] []

o

[]

0.4 0 o

@ o

i 2

[]

[]

:

: 4

?

;

:

6

•

•

&

'

Weeks after planting

Fig. 2. Cumulative N leaching-loss with time for pot chrysanthemums receiving the CRF Osmocote (14--14--14), at 1.68 (e), 2.52 (o) and 3.36 (o) g N/pot, and liquid feed at concentrations of 98 (e), 196 (D)and 294 ( o ) m g N/1.

tration in the leachate averaged 40 mg/1 throughout the crop cycle except for the last week. As shown by Fig. 1, the NO3-N concentrations in the leachates were either higher or lower than those in the applied solution. A similar result has also been reported by Gislerod and Selmer-Olsen (1980) for chrysanthemums grown in recirculated nutrient solutions. Whether the NO3-N concentration in the leachate is higher or lower than that in the applied solution is determined principally by the relative uptake of water and N O ; by the plant. If the NO3-N concentration in the leachate is greater than in the applied solution, then the plant absorbs water faster relative to the uptake of NO;. When the plant absorbs NO7 faster relative to water uptake, then the NO3-N concentration in the leachate is lower than in the applied solution. Therefore, with the 98 mg N/1 treatment, the uptake of N O ; by chrysanthem u m s was greater relative to water uptake for the first 9 weeks. With LF at the 2 higher rates, water absorption was greater relative to NO~ uptake, and

151 NO3-N concentrations in the leachate increased above those in the applied solution. Unlike the cumulative leaching loss curves for the Osmocote treatments which leveled off after 5 weeks, cumulative leaching losses of N with LF increased t h r o u g h o u t the crop cycle (see Fig. 2). This increasing loss of N is inherent with liquid feeding where the rate of N application is greater than the rate of N uptake by the plant. Comparison o f N losses from L F and CRF. -- The total a m o u n t of N leached with LF varied from 0.14 to 1.70 g/pot at N application rates of 1.21 to 3.57 g N/pot (Fig. 3). The amounts leached represent 12 and 48% of the applied N. With CRF, the N leached was about half that with LF at the same rate of N application (Fig. 3) ranging from 0.20 to 0.77 g N/pot at application rates of 1.68 to 3.36 g N/pot. As with LF, the percentage of the applied N lost through leaching also increased at higher rates of N application. Percentage losses of applied N varied from 12 to 23%. For the CRF, the N losses can also be expressed relative to the a m o u n t of N that was released during the experiment. Analysis of the Osmocote granules in pots after harvest revealed that 19.6--21.4% of the applied N remained. Thus, only about 80% of the applied N had been released during the l l - w e e k crop cycle. When N leached is plotted against N released, the leaching-losses of N for CRF are much closer to those for LF (Fig. 3).

o 1.6

1.2 O~ o "10

o.8

~

d

D/

ased

/

/

o/

z

o~/C.~R

F,applied

0.4

f |

;

,

,

,

o

N applied or released, g / p o t

Fig. 3. Total N lost through leaching for a crop of pot chrysanthemums as a function of the N applied as CRF or LF, and as a function of the amount of N released from the CRF during the 11-week crop cycle.

152 T h e d i f f e r e n c e in leaching-losses o f N b e t w e e n surface a p p l i c a t i o n s o f liquid f e e d a n d c o n t r o l l e d - r e l e a s e fertilizer d e p e n d s o n t h e m e t h o d o f c o m p a r i s o n . A c o m p a r i s o n o f leaching-losses can b e m a d e in several w a y s . F o r e x a m p l e , t h e r e c o m m e n d e d r a t e o f C R F c a n b e c o m p a r e d to a r e c o m m e n d e d L F c o n c e n t r a t i o n such as 2 0 0 m g N/1. A n o t h e r m e t h o d is t o c o m p a r e t h e leaching-losses w h e n t h e N a p p l i e d w i t h C R F equals t h e N a p p l i e d w i t h L F . Still a n o t h e r w a y is t o c o m p a r e losses w h e n t h e N released w i t h C R F is t h e s a m e as t h e N a p p l i e d w i t h L F . W h e n t h e s e 3 c o m p a r i s o n s are m a d e , using t h e d a t a f r o m this s t u d y (Fig. 3), leaching-losses w i t h L F are m o r e t h a n 4 t i m e s t h o s e w i t h C R F , a b o u t t w i c e t h o s e w i t h C R F , a n d a l m o s t t h e s a m e as those with CRF, respectively. REFERENCES Barton, H.M., 1977. Controlled release fertilizer and its use in hot climates. South. Florist Nurseryman, 89(46): 16--17, 35--38. Bunt, A.C., 1976. Modern Potting Composts. Pennsylvania State University Press, University Park, 277 pp. Carlson, R.M., 1978. Automated separation and conductimetric determination of ammonia and dissolved carbon dioxide. Anal. Chem., 50: 1528--1531. Furuta, T., 1976. Nitrogen fertilization of container-grown ornamentals. Am. Nurseryman, 143(12): 14,106--109. Gislerod, H.R. and Selmer-Olsen, A.R., 1980. The responses of chrysanthemum to variations in salt concentration when grown in recirculated nutrient solution. Acta Hortic., 98: 201--209. Holcomb, E.J., 1979. Cost and efficiency of slow-release fertilizer. Pa. Flower Growers Bull., 316: 9--10. Holcomb, E.J., 1980. How to increase fertilizer efficiency through slow-release formulations. Am. Nurseryman, 152(7): 9,38,40,42,44. Kofranek, T. and Lunt, O.R., 1966. Mineral nutrition programs for ornamentals. Florist Rev., 138(3577):15--16, 63--67. Leung, C.Y., 1970. A study of controlled-release nitrogen fertilizers. M.S. Thesis, University of California, Davis. Maynard, D.N. and Lorenz, O.A., 1979. Controlled-release fertilizers for horticultural crops. Hortic. Rev., 1: 79--140. Oertli, J.J., 1980. Controlled-release fertilizers. Fert. Res., 1: 103--123. Seeley, J.G. and Langhans, R.W., 1977. Floriculture crop production in the United States. HortScience, 12: 25--29. Sharma, G.C., 1979. Controlled-release fertilizers and horticultural applications. Scientia Hortic., 11: 107--129. Sharma, G.C. and Patel, A.J., 1978. Effect of nine controlled-release fertilizers on chrysanthemum growth and foliar analysis. J. Am. Soc. Hortic. Sci., 103: 148--150.