Evaluating stratified substrates effect on containerized crop growth under varied irrigation strategies

Authors: CRISCIONE, KRISTOPHER - Louisiana State University Agcenter; FIELDS, JEB - Louisiana State University Agcenter; Owen Jr, James - Jim; FULTZ, LISA - Louisiana State University Agcenter; BUSH, EDWARD - Louisiana State University

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2021
Publication Date: 2/1/2022
Citation: Criscione, K.S., Fields, J.S., Owen Jr, J.S., Fultz, L., Bush, E. 2022. Evaluating stratified substrates effect on containerized crop growth under varied irrigation strategies. HortScience. 57(3):400-413. https://doi.org/10.21273/hortsci16288-21.
DOI: https://doi.org/10.21273/hortsci16288-21

Interpretive Summary: Traditional bark-based substrates utilized in open-air production of horticultural crops have low water holding capacity which can lead to non-uniform rewetting patterns and inefficient usage of water resources. By stratifying the substrate, laying fine or fiber (i.e., coir or peat) amended bark over a coarse bark, producers can reallocate water within the container while still maximizing aeration to ensure healthy root development. Research herein demonstrated that stratified substrates could enhance crop quality and growth by allowing more available water to plant roots in the upper strata. The traditional soilless substrate commonly used by plant nurseries was incapable of maintaining adequate substrate moisture for plant roots until the next subsequent irrigation which resulted in severe water stresses and death. Plant shoot quality was enhanced by substrate stratification. There were little differences observed in microbial communities across substrate treatments with exception of sphagnum peat amended bark, which contained greater proportions of actinomycetes. The results show that with the stratified system, water sensitive crops such as the Loropetalum can be rescued under drought conditions during the fragile establishment period, when compared to using traditional pine bark.

Technical Abstract: Growers rely on soilless substrates to provide sufficient water and nutrients to containerized crops. Traditional bark-based substrates tend to have relatively low water holding capabilities which can lead to non-uniform rewetting patterns and inefficient usage of water resources. Engineering substrates to redistribute water dynamics and maximize aeration within the container may improve water resource efficiencies. The goal of this study was to evaluate whether more efficient irrigation schedules can be utilized when stratifying unique substrates within a container for added crop water and nutrient efficiency. Loropetalum chinense ‘Ruby’ liners were planted utilizing either a conventional pine bark or one of three stratified substrate treatments, including either a bark:peat, bark:coir, or fine bark layered on top of a coarse bark. The crops were grown under four different irrigation schedules including single daily application, single application at deficit levels, cyclic application, or cyclic deficit schedules. Stratified substrates improved crop growth, quality, and yield when compared to plants grown in conventional bark in the single application irrigation treatment. Upon final harvest, substrates positively influenced plant growth index (P<0.0001) whereas irrigation scheduling alone had no effect (P=0.6321). There was a strong interaction between substrate and irrigation schedules on ' growth index (P=0.0141). There were strong substrate effects on shoot dry weight (P=0.0060), root dry weight (P=0.0342), and growth index (P=0.0040). The stratified bark:coir treatment outgrew all other substrate treatments. Additionally, within all irrigation treatments, plants grown with the stratified bark:coir substrate had the highest survival ratings among the other substrate treatments, whereas the conventional bark had the lowest survival rates. Substrate and irrigation had an effect on nitrogen and potassium leachate concentrations (P=0.0107 and P=0.0004, respectively). Evaluation of microbial communities showed that substrate (P=0.0010) and the stratified layer (P=0.0010) had strong infleunces on the type of community present and the relative abundance in the treatments used herein this study. Speficailly, within cyclic scheduling, bark:peat actinomycete populations were significantly greater than other substrate treatments. Furthermore, under deficit irrigation, stratified substrate systems were able to mitigate crop water stress. The results indicate that with the stratified system, crops such as the Loropetalum can be rescued under drought conditions during the fragile establishment period, when compared to using traditional bark-based substrates.