Strategic timing and rate of phosphorus fertilization improves phosphorus-use efficiency in two contrasting cultivars of subirrigated greenhouse-grown chrysanthemum

Abstract

Greenhouse floriculture operations pose significant environmental risk due to extensive inputs of fertilizer, especially nitrogen and phosphorus (P). Recent evidence shows that the use efficiency for nitrogen or sulphur is markedly improved in subirrigated potted chrysanthemums (Chrysanthemum morifolium Ramat.) by supplying a moderate level of the nutrient during vegetative growth, and removing the entire nutrient suite at the onset of reproductive growth, without adverse effects on plant quality. Here, two split-plot experiments were conducted with subirrigated, potted, disbudded chrysanthemums grown in a peat:perlite mixture under greenhouse conditions (high- or low-ambient light) with inorganic orthophosphate (Pi) treatment (2.6 mmol L−1 Pi supplied during the vegetative and reproductive stages, and 2.6, 1.95, or 1.3 mmol L−1 Pi supplied during the vegetative stage only) as the main plot and cultivar (‘Olympia’ and ‘Covington’) as the subplot. Market quality plants with sufficient tissue P were produced even when Pi delivery was reduced by approximately 75% over the crop cycle, compared with industry standards. The primary mechanism for sustaining plant growth with decreasing Pi delivery was improved acquisition or uptake efficiency, although some changes in internal P-utilization efficiency were evident, including the remobilization of both organic P and Pi during inflorescence development. Differences in biomass yields, tissue P concentrations, content-based P-use efficiency (PUEC = mg shoot dry mass/mg shoot P content) with constant Pi acquisition, and uptake- versus remobilization-based P supply for inflorescence growth established that ‘Olympia’ has a greater P-utilization efficiency than ‘Covington’. This modified subirrigation practice could contribute significantly to low-input production of floricultural crops.

Commercial validation of a modified method for delivering low nitrogen, phosphorus, and potassium inputs to greenhouse-grown subirrigated pot chrysanthemums

“…Our early research on the nutrition of greenhouse-grown pot chrysanthemums used Sonneveld's solution as the industry standard, and confirmed that the production of market-quality plants and flowers is unaffected by removing entire nutrient supplies at bud break, and by supplying N and P levels as low as 9.3 and 1.3 mmol L 1 , respectively, during vegetative growth. (Shelp et al 2017(Shelp et al , 2020b. We also demonstrated that N/P/K levels (in mmol L 1 ) as low as 4.3 N, 0.65 P and 2.3 K produces market-quality plants with acceptable leaf N/P/K levels of 4.05.5% DM, 0.610.75% DM and 4.2-5.2% DM, respectively (Shelp et al 2020a;Shelp, B.J.…”

“…These findings indicate that the macronutrient use efficiencies (which can be defined as mg shoot DM/concentration of macronutrient supply) improved approximately 4-fold with decreasing macronutrient supplies. Based on our previous research on the N, P and sulphur nutrition of chrysanthemums, the primary mechanism for sustaining plant shoot growth with decreasing N/P/K supplies was likely enhanced acquisition or uptake efficiency, but given our experimental methodology, it was not possible here to quantify the relative importance of acquisition and internal utilization efficiencies (Shelp et al 2017(Shelp et al , 2020a(Shelp et al , 2020bSutton et al 2019).…”

“…Removal of the fertilizer supply at bud break would reduce the fertilizer cost to $76,000, and reduction of the fertilizer supply from 21.4 to 5.4 mmol L -1 N prior to bud break would further reduce the cost to $19,000. A closed subirrigation system would have less total savings as less fertilizer is used due to recycling (Shelp et al 2020b), but the same concept applies -reducing fertilizer rate results in proportional cost savings. The volume of concentrated nutrient-rich nutrient solution for management, and environmental contamination would also be decreased with our modified delivery practice.…”

“…Over the past decade, we modified the nutrient delivery practice in order to improve the macronutrient use efficiency of subirrigated pot chrysanthemums grown under research greenhouse conditions. Entire macro-and micronutrient supplies were removed during reproductive growth, and approximately 50-75% or less of the N/P/K levels in Sonneveld's solution (in mmol L 1 : 18.5 N/2.6 P/6.0 K; Sonneveld and Kreij 1987) was provided during vegetative growth, together with the essential micronutrients (MacDonald et al 2014;Shelp et al 2017Shelp et al , 2020aShelp et al , 2020b. There were no visible signs of N/P/K deficiency and the plant/flower yields and quality were unaffected.…”

Optimizing manganese and iron delivery for contrasting cultivars of subirrigated greenhouse-grown pot chrysanthemums

“…In our research, we improved NUE in modern cultivars of greenhouse-grown, subirrigated chrysanthemums, without adversely affecting crop production. The entire macro-and micronutrient supplies were removed during reproductive growth, and only 25-50% of the recommended industry levels of macronutrients were provided during vegetative growth, together with the recommended industry level of micronutrients (MacDonald et al 2014;Shelp et al 2017Shelp et al , 2020Shelp et al , 2021bSutton et al 2019;Duncan Stephens et al 2021).…”