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William R. Argo and John A. Biernbaum

Subirrigated Easter lilies were grown in five commercially formulated root media using one water-soluble fertilizer applied independently to each medium based on water-holding capacity and water loss. The number of irrigations ranged from 12 to 20 and the amount of applied water ranged from 5.3 to 6.8 liters for the uncovered media treatments. When the root-medium surface was covered with an evaporation barrier, the average amount of applied water was reduced by 35% compared to the uncovered media. The largest effect on root media pH was between uncovered and covered media due to the reduced amount of water applied. Similar macronutrient concentrations were measured in the five media during the experiment with few exceptions. The greatest differences in nutrient concentrations were found within the pots. The top 2.5 cm (top layer) contained nutrient concentrations up to 10 times higher than those measured in the remaining root medium (root zone) of the same pot. Covering the root-medium surface with an evaporation barrier reduced the stratification of fertilizer salts. Root-zone soluble salt concentrations of plants in the covered pots were similar to those of uncovered plants even though 36% less fertilizer was applied to the covered plants.

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Mark V. Yelanich and John A. Biernbaum

`V-14 Glory' poinsettias (Euphorbia pulcherrima Willd. ex Klotzsch) were fertilized at every irrigation with solutions containing 7, 14, or 28 mol N/m3 at four leaching fractions (LFs) of 0, 0.1 to 0.2, 0.3 to 0.4, or 0.5 to 0.6 or with subirrigation. The N applied ranged from 44 to 464 mmol/pot applied over 12 to 25 irrigations. Medium NO3-N and K concentrations and electrical conductivity were highest at the highest fertilizer concentration and lowest LF throughout cropping. Phosphorous concentration in the medium declined until week 12, when phosphoric acid was added for pH adjustment. Subsequently, medium P concentration was highest in treatments with the highest LF. Final shoot height, plant dry mass, and leaf area decreased as fertilizer concentration increased. Highest fresh mass, bract area, and shoot: root ratio were obtained with 14 or 28 mol N/m3 and a 0.55 LF or with 7 mol N/m3 and a 0.15 LF. Leaf N concentration was lower with subirrigation than with surface application. Leaf P and Mg were lower at higher LFs or with subirrigation, but leaf K was not influenced by the treatments.

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William R. Argo and John A. Biernbaum

Rooted cuttings of `Gutbier V-l 4 Glory poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) were grown in 15-cm pots using two irrigation methods, two water-soluble fertilization schedules, and two preplant root-media fertilization rates. No difference in shoot growth occurred with either top watering with 33% leaching or subirrigation. The top 2.5 cm (top layer) contained nutrient concentrations up to 10 times higher than those measured in the remaining root medium (root zone) of the same pot with both irrigation methods. Constant applications of28 mol N/m3 water-soluble fertilizer (WSF) limited shoot and root growth as measured at 3 and 8 weeks compared to a weekly increase in the concentration of WSF from 0 to 28 mol N/m3 in 7 mol N/m3 increments over a S-week period. The additional incorporation of 0.27 kg·m-3 mineral N to Metro Mix 510 before planting had no effect on fresh- or dry-weight accumulation. When the root-medium surface was covered by an evaporation barrier, 46% less water and 41% less N fertilizer were applied to plants of similar size, and higher root-zone nutrient levels were maintained over the 8 weeks of the experiment. The evaporation barrier had the greatest effect on increasing root-zone nutrient concentrations and reducing the growth of subirrigated plants.

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William R. Argo and John A. Biernbaum

Hybrid impatiens (Impatiens Wallerana Hook. F.) were planted in a peat-based medium containing two dolomitic liming materials (1.8 kg Ca(OH)2·Mg(OH)2/m3 or 8.4 kg CaCO3·MgCO3/m3) and subirrigated for 17 weeks using four irrigation-water sources (IWSs) with varied bicarbonate alkalinity, Ca2+, Mg2+, and SO4-S content and three water-soluble fertilizers (WSFs) that contained (in mg) 200N-20P-200K/liter but a variable NH4: NO3 ratio, Ca2+, Mg2+, and SO4-S content. The factorial arrangement of the IWS and WSF resulted in a range of Ca2+, Mg2+, and SO4-S concentrations varying by a factor of 10. After 8 weeks, medium pH ranged from 4.5 to 8.5. The maximum critical medium pH for PO4-P uptake was 7.4 to 7.7, which probably was due to a change in most of the water-soluble P to the less-available HPO4 2- form. Lime type did not affect the long-term increase in medium pH, Ca2+, and Mg2+ concentrations with nutrient solutions containing low NH4 +-N and high Ca2+ and Mg2+. The carbonate lime buffered the medium pH and Ca2+ and Mg2+ concentrations with nutrient solutions containing high NH4 +-N and low Ca2+ and Mg2+ compared to that measured with the hydrated lime. With both lime types, there was a linear increase in tissue Ca and Mg as the applied concentrations of the various nutrient solutions increased from 18 to 210 mg Ca2+/liter and 7 to 90 mg Mg2+/liter. The relationship was similar for both lime types up to week 8, after which tissue Ca and Mg decreased more rapidly with the hydrated lime and low solution Ca2+ and Mg2+ compared to that of the same carbonate lime treatments. The minimum critical SO4-S concentration in the applied nutrient solution for plant uptake was 30 to 40 mg S/liter. Below this concentration, tissue S decreased rapidly; above, there was little effect on tissue S.

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William R. Argo and John A. Biernbaum

Using incubation and container culture with subirrigation for up to 28 days, three experiments were conducted with six liming materials of different particle sizes and six blended preplant nutrient charge (PNC) fertilizers. Liming material, particle size, and incorporation rate had an effect on the initial pH (3.5 to 6.1) and the final stable pH (4.8 to 7.8) with one type of Canadian sphagnum peat that did not contain an incorporated PNC. Saturated media extract (SME) Ca and Mg concentrations were <25 and 15 mg·liter-1, respectively, for both pulverized and superfine dolomitic lime at incorporation rates up to 7.2 kg·m-3. For the blended PNC fertilizers in media containing lime, initial electrical conductivity (EC) and SME nutrient concentrations ranged from (EC) 1.0 to 2.9 dS·m-1, (mg·liter-1) 60 to 300 N, 4 to 105 PO4-P, 85 to 250 K, 120 to 400 Ca, and 60 to 220 Mg. However, within two days, the rapid stratification of fertilizer salts within the pot caused macronutrient concentrations to increase in the top 3 cm of root medium (top layer) by an average of 180% and decrease in the remaining root medium in the pot (root zone) by an average of 57% compared to that measured in the medium at planting. Nutrient concentrations in the top layer continued to increase even when those in the root zone fell below acceptable levels recommended for an SME. The importance of fertilizer salt stratification within a pot lies in the reduced availability of nutrients to the plant and illustrates the limited persistence of the PNC fertilizers. Testing nutrients in container media several days after planting rather than in freshly mixed media may be more representative of the starting point for a nutritional management program.

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John A. Biernbaum, Mathieu Ngouajio, and Laurie Thorp

How do you teach community supported agriculture (CSA) principles, small-scale organic farming, and local food issues at a major land grant university and develop related small-scale farming research and outreach? You create a place and opportunities for students, staff, and faculty to work together with the soil and plants to raise food in a non-classroom farm setting. After several years of discussion and obtaining funding, the Michigan State University (MSU) Student Organic Farm (SOF) CSA started in May 2003 with 25 memberships and increased to 50 after 1 year. The farm allows experiential learning of CSA management, crop selection, scheduling, maintenance, harvest, and organic farming methods. The CSA helps many MSU students and faculty see the value of supporting local organic food systems. With more than 3 years of experience working with students to run the SOF and the CSA, we are in the process of developing an organic farming certificate program. A total of 40 credits will include 12 months on campus plus a 16-week on-farm internship. The program has three major components: 1) organic farming courses with seven one-credit courses; 2) horticultural crop production courses with eight courses for a total of 15 credits; and 3) approximately 20 credits of experiential course work combined with classroom and independent learning.

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William R. Argo and John A. Biernbaum

`V-14 Glory' poinsettias (Euphorbia pulcherrima Willd. ex Klotzsch) were grown in five root media using top watering with 20% leaching for 112 days. Root media with a high water-holding capacity required fewer irrigations and fertilizer applications than those with a lower water-holding capacity. However, similar amounts of water were applied and leached with both types of root media over the entire experiment. The reduction in the number of fertilizations was compensated for by an increase in the amount (volume) of fertilizer applied at any one irrigation. The greatest differences in root-media nutrient concentrations were found between the top 2.5 cm (top layer) and the remaining root medium within the same pot (root zone). After 58 days, when fertilization with water-soluble fertilizer (28.6N–0P–8.5K mol·m–3) was stopped, nutrient concentrations in the top layer were 3 to 6 times greater than those in the root zone for all five root media tested. For the final 42 days of the experiment after fertilization was stopped, nutrient concentrations in the root zone remained at acceptable levels in all root media. The nutrients contained in the top layer may have provided a source of nutrients for the root zone once fertilization was stopped.

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Mark V. Yelanich and John A. Biernbaum

A model was constructed to dynamically simulate how the nitrogen concentration changes in the root zone of a pot grown chrysanthemum. The root zone concentration of nitrogen is predicted at any time during the crop by predicting the root zone contents of nitrogen and water. The root zone content of nitrogen is predicted by integrating the rates of nitrogen applied, taken up by the plant and entering the top layer of the pot. The root zone water content is predicted by integrating the rates of water applied, evaporated from the media surface and transpired by the plant. Simple models were constructed to predict the various rate processes. For example the rate of nitrogen uptake was modeled as a function of the dry mass accumulation and was broken down into demands of nitrogen by the plant for maintenance of the current dry mass and for support of new growth. Dry mass accumulation was modeled as a function of the amount of PPF which could be intercepted by the plant. The model was validated using plants grown in growth chambers and greenhouses at various PPF levels and fertilizer concentrations. The model will be used to test the risks involved in using various fertilizer strategies and to develop more efficient fertilization strategies.

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William R. Argo and John A. Biernbaum

Impatiens were planted into peat-based media containing two dolomitic liming materials [Ca(OH)2·Mg(OH)2 at 1.8 kg·m–3 or CaCO3·MgCO3 at 8.4 kg·m–3] and subirrigated for 17 weeks using four irrigation water qualities (IWQ) with varied alkalinity, Ca2+, Mg2+, and SO4-S content and three water-soluble fertilizers (WSF) with varied NH4:NO3 ratio, Ca2+, Mg2+, and SO4-S content. After 8 weeks, medium pH ranged from 4.5 to 8.5. Lime type did not affect the long-term increase in medium pH, Ca2+, and Mg2+ concentrations with IWQ/WSF solutions containing low NH4-N and high Ca2+ and Mg2+ concentrations. The carbonate lime did buffer the medium pH, Ca2+, and Mg2+ concentrations with IWQ/WSF solutions containing high NH4-N and low Ca2+ and Mg2+ concentrations. With both lime types, there was a linear increase in tissue Ca and Mg as the applied concentrations increased from 0.5 to 4.0 mol·m–3 Ca2+ and 0.3 to 3.0 mol·m–3 Mg2+ with the various IWQ/WSF. The relationship was similar for both lime types up to week 8, after which tissue Ca and Mg decreased with the hydrated lime and low solution Ca2+ and Mg2+. Relationships were also developed between the applied SO4-S concentration and tissue S and medium pH and tissue P.