HORTSCIENCE 52(9):1288–1292. 2017. doi: 10.21273/HORTSCI12122-17 Krause, 2014), a similar concern of N immo- bilization was voiced by nursery growers (J. Altland, personal observations, unpublished). Effect of Rice Hull Mulch on Nutrient In a review of mulch use in urban landscapes, Chalker-Scott (2007) explained that high Concentration of Fertilized carbon to nitrogen ratio (C:N) is incorrectly assumed by many practitioners to immobilize Irrigation Water fertilizer N and thus deprive plants of suffi- cient nutrients. Chalker-Scott (2007) goes on James E. Altland1 to assert that mulches do not affect nutrition USDA-ARS, Application Technology Research Unit, 27 Horticultural Insects of landscape plants. There are numerous Research Lab., 1680 Madison Avenue, Wooster, OH 44691 experiments in field soils that support this assertion and show mulches do not adversely Jennifer K. Boldt affect nutrient uptake of field-grown crops USDA-ARS, Application Technology Research Unit, Greenhouse Production (Broschat, 2007; Ram et al., 2003; Trinka and Pritts, 1992). However, this generalization Research Group, 2801 W. Bancroft Street, Mail Stop 604, Toledo, OH 43606 about interactions between mulch and fertil- Additional index words. nitrate, phosphate, potassium, sunflower, plant nutrition izer in field crops might not be applicable to container crops. Altland and Lanthier (2007) Abstract. Parboiled rice hulls (PBH) have been shown to be an effective mulch for weed reported that container-grown hydrangea control in container crops. As with other mulch products, there is concern that PBH [Hydrangea macrophylla (Thunb.) Ser. mulch would interfere with nutrient delivery to the crop. The objective of this research ‘Fasan’] with controlled release fertilizer was to determine the effect of PBH mulch on nutrient concentration of fertilized (CRF) placed below the mulch were larger irrigation water as it passes through the mulch layer, and the subsequent effect on growth and had higher foliar N concentration com- and nutrition of container-grown sunflower (Helianthus annuus). Parboiled rice hull pared with those with CRF placed above the mulch was placed in Buchner funnels at a depth of 0, 0.63, 1.25, or 2.50 cm. Irrigation was mulch. The implication was that N from CRF applied with a water-soluble fertilizer (20N–4.4P–16.6K) injected at a concentration of placed above the mulch was partially immo- L 100 mg·L 1 N. Filtrates were collected after passing through the PBH in the Buchner bilized by the mulch layer. Likewise, Glenn funnels and analyzed for nutrient concentration. In a separate study, sunflower in no. 3 et al. (2000) showed that recycled paper containers were mulched with the same depths of PBH and irrigated with water fertilized mulch reduced petunia (Petunia floribunda similar to that in the funnel experiment. Parboiled rice hull mulch caused a temporary Hort. ‘Midnight Madness’ and P. grandiflora L + + and slight decrease in NO3 and NH4 concentration. Phosphate and K concentrations Hort. ‘Ultra Blue’) growth and leachate N generally increased with each irrigation event. Calcium and Mg exhibited an inverse when CRF was placed above the mulch layer. relationship where the PBH mulch decreased Ca and increased Mg concentrations in the The objective of this research was to de- filtrates. Despite these measured differences in the chemical properties of water passing termine specifically how PBH mulch affects through the mulch layer, there were no measurable differences in sunflower growth or the nutrient concentration of irrigation water physical appearance, and only minor and inconsequential differences in plant nutrient passing through the mulch layer, and sub- status. Rice hull mulches are likely to have very minor effects on container crop nutrition sequently how this affects substrate and plant with no adverse effect on plant growth over a 6 week production cycle as used in this nutrition. experiment. Materials and Methods Numerous mulch products have been silicicola (Small) E. Murray] and southern Direct measurement of filtrates. Two- evaluated for use in container crops. Pine magnolia (Magnolia grandiflora L.) provided piece, PVC Buchner funnels (13.1 cm i.d., bark nuggets have been shown to provide control of redroot pigweed (Amaranthus ret- 6.6 cm tall, Fisher Scientific, Waltham, MA) effective control of mulberry weed [Fatoua roflexus L.) and large crabgrass [Digitaria were randomly assigned to receive PBH villosa (Thunb.) Nakai] (Penny and Neal, sanguinalis (L.) Scop.]. (Riceland Foods, Inc., Stuttgart, AK) at 2003), prostrate spurge (Chamaesyce macu- Parboiled rice hulls have been shown to a depth of 0, 0.63, 1.25, or 2.50 cm. It was lata L.), eclipta (Eclipta alba L. Hassk) provide excellent control of flexuous bittercr- established that 2.5 cm depth of PBH (Cochran et al., 2009), bittercress (Card- ess (Cardamine flexuosa With.), liverwort weighed 44 g so that replicate funnels could amine spp.), and oxalis (Oxalis stricta L.) (Marchantia polymorpha L.) (Altland and be uniformly mulched by weighing 0, 11, 22, (Richardson et al., 2008). In each of the Krause, 2014), and creeping woodsorrel or 44 g of PBH for the 0, 0.63, 1.25, or 2.50 aforementioned studies, weed control was (Oxalis corniculata L.) (Altland et al., cm treatments, respectively. Funnels were shown to improve with increasing depth of 2016a). Parboiled rice hulls prevent establish- placed on a greenhouse bench equipped with pine bark mulch. Wilen et al. (1999) showed ment of new weed seed by drying quickly an overhead irrigation system and fixed that composted greenwaste, pecan [Carya following irrigation, resulting in insufficient pattern nozzles (Rain Bird 5H; Rain Bird illinoinensis (Wangenh.) K. Koch] shells, moisture to support germination and estab- Corp., Azusa, CA). Funnels received over- and pine (Pinus taeda L.) bark at a depth of lishment of new weeds. Parboiled rice hulls head irrigation consisting of city tap water 2.5 cm provided excellent control of creeping are less effective in preventing germination injected (D14MZ2; Dosatron International woodsorrel (Oxalis corniculata L.), northern of weed seed preexisting on the substrate Inc., Clearwater, FL) with a commercial willow herb (Epilobium ciliatum Raf.), and surface before mulch application. To prevent complete fertilizer with micronutrients common groundsel (Senecio vulgaris L.), but germination and establishment of preexisting (Jack’s 20N–4.4P–16.6K–0.15Mg–0.02B– only moderate to poor control of annual blue- weed seed, a sufficient mass must cover the 0.01Cu–0.1Fe–0.05Mn–0.01Mo–0.05Zn; JR grass (Poa annua L.). Ferguson et al. (2008) substrate surface to physically impede ger- Peters, Inc., Allentown, PA) at a concentra- showed that a 3.7 cm layer of wood chip mination (>500 g·m–2 or a depth of 1.25 cm) tion of 100 mg·L–1 N. Each funnel was placed mulches from southern redcedar [Juniperus (Altland et al., 2016). over a 400 mL glass jar (Fisher Scientific) so A common concern about organic that the fertilized irrigation water passing Received for publication 17 May 2017. Accepted mulches is that they impose nitrogen (N) through the mulch layer would collect in for publication 11 July 2017. deficiency on crops they surround. After the jar beneath, and furthermore, only water 1Corresponding author. E-mail: James.Altland@ initial reports on the utility of PBH for weed passing through the funnel (and no other ARS.USDA.GOV. control in container crops (Altland and extraneous irrigation water) would enter into 1288 HORTSCIENCE VOL. 52(9) SEPTEMBER 2017 the jar. The irrigation system was run for (N) was determined by measuring 2.5 mg Reverse osmosis (RO) water was added to 10 min per day, resulting in an application of of dry tissue into tin capsules (Costech the point of saturation. The substrate slurry 1.3 cm of water. About 30 min after Analytical, Valencia, CA) and analyzing was allowed to come to equilibrium for 24 h. irrigation ceased, the fertilized irrigation with a CHNS/O Perkin Elmer Elementar Afterward, the liquid phase of the slurry was water that filtered through the mulch was Analyzer (PerkinElmer, Waltham, MA). extracted by pouring over a PVC Buchner collected from the jars beneath each funnel. Other macronutrients and micronutrients funnel (13.1 cm i.d., 6.6 cm tall, Thermo Samples were filtered through GF/F binder- were determined by first processing sam- Fisher Scientific) fitted with a fiberglass free borosilicate glass fiber filter paper ples with microwave digestion (MARS 6; filter paper (G6, Thermo Fisher Scientific). (Whatman Ltd., Kent, UK) to remove parti- CEM Corp., Matthews, NC), then injection in The Buchner funnels were attached to an cles greater than 0.7 mm. The filtrate was an optical emission spectrometer (iCAP 6300 erlenmeyer flask and placed under vacuum poured into 5 mL autosampler vials, capped, Duo). The elemental content of PBH was also to facilitate extraction of the water from the and analyzed using ion chromatography (ICS determined by subjecting five unused samples substrate and through the filter paper. Solu- 1600 Ion Chromatography System; Dionex, to the same preparation and analyses as the tion pH was determined with a pH/ion Bannockburn, IL) for concentrations of ni- sunflower tissue samples. analyzer (MA 235; Metler Toledo, Colum- – + trate (NO3 ), ammonium (NH4 ), phosphate Immediately after leaf tissue harvests, bus, OH) and EC with a conductivity meter 3– (PO4 ), potassium (K), calcium (Ca), mag- shoot dry weight (SDW) was determined by (Fisher 06-662-61, Thermo Fisher Scien- 2– nesium (Mg), and sulfate (SO4 ). There were removing the aboveground portion of the tific). Samples were subsequently filtered six replications per mulch depth arranged on plant, oven drying at 55 °C for 3 d, and through GF/F binder-free borosilicate glass a single bench in a completely randomized weighing. Substrates were analyzed for pH, fiber filter paper (Whatman Ltd.) to remove design. Samples were collected daily for nine electrical conductivity (EC), and water ex- particles greater than 0.7 mm.