Determination of nutrient availability of organic fertilizers for potential use on greenhouse crops

Part 2. Production of potted chrysanthemums with organic fertilizers

A research report by Theo J. Blom¹ and Paul Voroney²
University of Guelph, Guelph, ON, N1G 2W1

In Part 1, we described how various organic fertilizers mineralized in various substrates used in a greenhouse (rock wool, soil, peat moss and coco coir).

For Part 2 of the project, a crop of potted chrysanthemums was grown in either peat moss or coco coir supplemented with organic fertilizers. The practice of using inorganic soluble fertilizers was used as the control and both treatments received approximately the same amount of N, P and K per pot. The organic fertilizers were applied as a pre-plant while the inorganic nutrients were applied as a post-plant in the irrigation water for the control treatment. The selection of the organic fertilizers for providing adequate N, P and K was based on results obtained from the first part of the study, in which it was concluded that alfalfa had an early release of nutrients.

Two experiments were set out to determine if a crop of potted mums could be produced using solely organic fertilizers. An additional objective was to determine if nutrients were mineralized from the organic amendments in these plant-substrate systems over the production period (~10 weeks). There were 2 cultivars of mums planted, Brighton and Rockport.

Experiment A:

Based on previous results, two mixes were prepared using a peat / perlite (70/30 V/V) substrate with limestone added to adjust the pH to 6. This basic mix received supplements to provide 0.5g N, 0.3g P₂O₅ and 0.5g K₂O per 1L of substrate. Alfalfa (A) or bone meal (B) were used as the base organic fertilizers and supplemented with rock phosphate and/ or seaweed in order to obtain the minimum nutrient requirements (Table A1).

Table A1. The amendments for three substrates (A, B, or C) based mainly on alfalfa or bone meal, or a combination of both in order to provide a minimal supplementation of 0.5g N, 0.3g P2O5 and 0.5g K2O per 1L of substrate (1X rate).

Code (name)	Alfalfa	Bone meal	Rock phosphate	Seaweed
	Rate in g / 10 L of substrate
A (alfalfa)	100	0	13.6	0
B (bone meal)	0	250	0	16.6
C(alfalfa / bone meal)	50	125	0	8.3

Analyses for alfalfa: 5-1-5; bone meal: 2-14-0; rock phosphate: 0.6-15-0; seaweed: 0-0-30

There were also substrates prepared with double the amendment rate, or 1.0 g N, 0.6 g P₂O₅ and 1.0 g K₂O per 1L of substrate (2X rate). A standard soluble fertilizer, Plant Products 20-10-20 dissolved in water, was used as the reference treatment. The control received no supplementation to the substrate prior to planting other than for pH control.

Single rooted cuttings of chrysanthemums (cv. ‘Brighton’ and ‘Rockport’) were planted into 11-cm diameter pots (volume of pot ~1L) using the substrates with amendments as outlined above (A1, B1, C1, A2, B2 and C2). The pots containing either cultivars were placed in troughs. Those treatments receiving organic fertilizers were irrigated with de-ionized water while the control pots were watered (on demand) with a nutrient solution that provided 500 mg N, 250mg P₂O₅ and 500 mg K₂O per pot. The control plants were provided with 1L / pot of 250 mg N, followed by 1L / pot of 200 mg N and then 1L / pot of 50 mg N using 20-10-20. This way all pots received 0.5g N, 0.25 g P₂O₅ and 0.5 g K₂O. After the liquid feed was exhausted, the pots were irrigated with clear water. The control plants were placed on separate troughs. Irrigation frequency for all troughs was similar. Each trough was filled with 30 pots (2 cultivars, 3 substrates and 5 plants / experimental unit).

The date of planting was March 4, 2009, and a long-day regime (night time interruption lighting was provided between 22:00hr until 02:00hr. After 3-weeks of growth plants were pinched back to 7 leaves and given another 1 week of long-day regime after which the plants were exposed to (natural) short days. The greenhouse temperature was maintained at 19/19ºC for D/N heating and 21/21ºC for ventilation. Plants were evaluated after 11 weeks for plant height, number of side shoots, leaf surface area as well as fresh and dry weight of aerial growth.

Results

The potted chrysanthemums grown with alfalfa as the main organic fertilizer at the 500 or 1000 mg N/ pot rate were similar in aerial portion dry matter production as the control treatment at 500 mg N / pot (Figure A1). Substrates based primarily on bonemeal performed less than the ones based on alfalfa. Plants grown with bone meal at the 2X rate showed phytotoxicity, and hardly or no side shoots(data not shown). The results for the leaf area of the leaves of the top 2 shoots showed a similar trend (Figure A2).

Table1

Figure A1. The effect of organic fertilizers (alfalfa, bone meal or a combination of both) as a pre-plant compared to an inorganic fertilizer in the liquid form(control) at different rates of nitrogen on the aerial dry weight of potted chrysanthemums. Data represent mean of 18 plants. The error bars represent the standard error.

Figure A2. The effect of organic fertilizers (alfalfa, bone meal or a combination of both) as a pre-plant compared to an inorganic fertilizer in the liquid form(control) at 2 rates of nitrogen on the total leaf area of a potted chrysanthemums. Data represent the mean of 18 plants with the error bars representing the standard error of the mean.

Experiment B.

The objective of this experiment was to determine if any of the nitrogen containing organic fertilizers would be as good as the control plants (liquid feed only), using either coco coir or peat moss as the growing substrate.

Materials and Methods
For this experiment, un-amended coco coir and peat/perlite substrate (only limestone was added) were prepared with various organic fertilizers. The goal was to provide equal amounts of nitrogen to each of the two mixes (Table B1) using the various organic substrates containing nitrogen. Thus, only 7 organic substrates were used. In addition to the seven base organic fertilizers, additional phosphorous and/or potassium was added so that all seven treatments were supplemented with 0.5 g N, 0.3 g of P₂O₅ and 0.5 g K₂O per 1L of substrate. Due to the particle size of the Toronto pellets (TO pellets), the pellets were pulverized before mixing with the potting substrate. Single rooted cuttings of 2 chrysanthemum cultivars (Brighton and Rockport) were planted into 11-cm diameter pots (volume of pot ~1L) so that each pot contained 500 mg N, 300 mg of P₂O₅ and 500 mg K₂O. The control pots were filled only with pH adjusted (to pH 6) substrate (peat/perlite 70/30 V/V). The substrates supplemented with organic fertilizers were placed on troughs, which were irrigated with de-ionized water. The control plants were placed on separate troughs and fertigated with liquid fertilizer (Plant Products 20-10-20). The control plants were watered with a solution to supply 500 mg N, 250mg P₂O₅ and 500 mg K₂O per pot. Each control pot was irrigated initially with a total of 1L of 250 mg N, followed by 1L of 200 mg N and then 1L of 50 mg N using 20-10-20. After the liquid feed was exhausted, the pots were given DI-water. Irrigation frequency for all troughs was similar. Each trough had 35 pots (7 substrates and 5 plants / experimental unit). The base substrate, peat moss and coco coir, as well as the 2 cultivars were kept on separate troughs.

Date of planting was March 4, 2009. Plants were pinched at 7 leaves on March 24, 2009, and were provided a long day regime (night time interruption lighting was provided between 22:00hr until 02:00hr) until March 31, 2009, after which the plants were provided with natural short days. Temperature was maintained at 19/19ºC for D/N heating and 21/21ºC for ventilation. Evaluation of plants took place on May 25, 2009.

Analyses for alfalfa: 5-1-5; bone meal: 2-14-0; rock phosphate: 0.6-15-0; and seaweed: 0-0-30

Table B1. Composition for supplementation of seven organic fertilizers to soilless substrate (peat moss based or coco coir) so that the substrate contains 5 g of N and a minimum of 3 g of P2O5 and 5 g K2O per 10L of substrate.

Main organic fertilizer	Analysis	Rate for 5 g N / 10L	Rock phosphate	Seaweed
		( g / 10L)
1.Feather meal	12.5 – 0 – 0	40	20.4	16.6
2.Bone meal	2 – 14 – 0	250	0	16.6
3.Blood meal	12 – 0 – 0	41.5	20.4	16.6
4.Alfalfa	5 - 1 – 5	100	13.7	0
5.Cornplus	8 -1 – 6	62.5	16.3	0
6.TO pellets	2.9 – 7.4 – 0.1	172	0	16.5
7.Rock phosphate	0.6 – 14.7 - 0	833	0	16.6

Results
The results from the plant growth test showed that plants in coco coir substrate did not grow as well as those grown in a peat/perlite substrate. Plants grown in coco coir had about 25% smaller leaves (Figure B1) and also 25% less dry weight (Figure B2). Plants grown in coco coir often showed yellowing and/or necrotic leaves. Plants grown in the peat/perlite substrate amended with either alfalfa, rock phosphate or TO pellets showed plant growth which was similar to the control plants.

Figure 1b

Figure B1. The effect of organic fertilizers applied as a pre-plant to a soilless substrate (either peat moss or coco coir) on the leaf area of the upper 2 shoots of a pinched potted chrysanthemum. Each treatment received 500 mg of N, 300 mg of P2O5 and 500 mg K2O per pot. The control plants (in peat moss only) received liquid fertilizer through subirrigation. Data represent the mean of 12 plants. The error bar represents the standard error.

Figure B2

Overall Summary of Part 2

In this project, we compared the rate of mineralization of a number of organic compounds such as alfalfa, corn meal, bone meal, blood meal, feather meal, rock phosphate and TO pellets (waste product from Toronto waste water treatment plants) when applied to either rock wool, peat moss, coco coir or soil. In one part of the project, the organics were mixed with the growing substrates at a certain amount of nitrogen per litre of substrate (0.5g/L) and 2 different substrate analyses were used to determine what rate of mineralization occurred using these substrate mixes. Besides the difficulty of how to determine the rate of mineralization, it is quite evident that topsoil mineralizes the organics quite well over time. More inert/sterile media such as rock wool and coco coir showed negligibe rates of mineralization of the organics, while peat moss was somewhat in between the top soil and rock wool or coco coir. The organic material, which showed the greatest promise, was alfalfa. This material appears to have a significant amount of soluble nitrogen, even after 2 months, the amount of mineralized nitrogen appeared to be only about 30% of the total supplied.

General conclusions

It is essential that organic fertilizer amendments are mineralized (ie. converted to inorganic forms by microorganisms) for their nutrients to become available for uptake by the plants. The results of our incubation studies, where various organic fertilizers had been added to different substrates on a volume basis, showed that rock wool and coco coir had no mineralization over a period of 9-16 weeks. The highest rate of mineralization was obtained by a non-pasteurized mineral topsoil, while peat moss showed some mineralization. When chrysanthemums were grown in a peat moss substrate amended with different organic fertilizers, the growth of the plants were comparable to the control (inorganic form). However, when coco coir was used as the substrate, the growth of the chrysanthemums was well below compared those grown in peat moss.

Overall Summary

In this project, we compared the rate of mineralization of a number of organic compounds such as alfalfa, corn meal, bone meal, blood meal, feather meal, rock phosphate and TO pellets (waste product from Toronto waste water treatment plants) by mixing them with either rock wool, peat moss, coco coir or soil. The main interest was in the mineralization into inorganic nitrogen. In one part one of the project, the organics were mixed with the growing substrates at a certain amount of nitrogen per liter of substrate (0.5g/L) and 2 different substrate analyses were used to determine what rate of mineralization occurred using these substrate mixes over time. There were no plants in the substrates. Besides the difficulty of how to determine the rate of mineralization, it is quite evident that topsoil mineralizes the organics quite well over time (80% recoverable as soluble inorganic nitrogen after 9 weeks). More inert/sterile media such as rock wool and coco coir showed negligible rates of mineralization of the organic fertilizers, while peat moss was somewhat in between the top soil and rock wool or coco coir. The organic material, which showed the greatest promise, was alfalfa. This material appeared to have a significant amount of soluble nitrogen. Even after 2 months, the amount of mineralized nitrogen appeared to be only about 30% of the total supplied.

In the second part of the project, we determined what the effects of plants would be and whether we could use organic materials to grow an adequate plant in either peat moss or coco coir as the basic substrate. Chrysanthemums were chosen as the test species. It turned out that peat moss was a suitable substrate while coco coir was not when amended with organic fertilizers. Alfalfa, corn meal (Corn Plus), rock phosphate and TO pellets were adequate compared to the control (liquid feed).

To learn more, see Part 1...

Author Locations and Affiliations
(1) University of Guelph, Department of Plant Agriculture, Guelph, ON, N1G 2W1, E-mail: tblom@uoguelph.ca
(2) University of Guelph, School of Environmental Science, Guelph, ON, N1G 2W1, E-mail: pvoroney@uoguelph.ca

Posted December 2010