Several acres of hazelnuts have been established at NWREC to evaluate the effect of different irrigation rates and application methods on young, newly planted hazelnut trees, and to investigate how supplemental water affects growth and yield as the trees age. Oregon hazelnuts have historically been farmed without irrigation, but as the climate trends towards hotter, drier summers, it appears that irrigation benefits trees, particularly during the first couple of years. Adequate water helps young trees develop stronger root structures and reduce stress, which can lower the attraction of certain pests including Pacific flatheaded borer. We are currently testing different rates of irrigation applied using drip, microsprinklers, and subsurface drip and thus far it appears that tree growth and yield benefit from water.
Stem water potential is similar to measuring a tree’s blood pressure. It is a measurement of how much pressure is required to force water up through the stem of the leaf. Higher numbers indicate more pressure is required to push water out of the stem, which means greater water stress. Recommended stem water potential numbers have not yet been developed for the new varieties of hazelnuts being planted. By accurately applying the optimum amount of water to enhance tree growth while minimizing waste, growers will be able to fine-tune their irrigation regime to maximize yields while minimizing the use and cost of water. We evaluated water stress of trees that differ in variety, age and irrigation management from 2016-20, and are planning to use the data to generate guidelines for Oregon hazelnut growers soon.
We have found that there is a significant effect of irrigation on yield when they begin bearing after about 4 years. While drip irrigation did not perform as well in our trials, the wetted area from our 2 emitters is much smaller compared with the industry standard drip tape, which will wet a larger area. Still, this research does show that trees do benefit from having the total root area irrigated, which can be achieved by full coverage microsprinklers. We also found that high and medium irrigation rates resulted in similar yields within drip and microsprinkler plots. The high rate of irrigation (150% Eto) should in most weeks be excessive, whereas low (50% Eto) would be deficit irrigation.
When we looked at cross sectional area of trees (diameter of tree trunks) there is a very clear trend with increased irrigation resulting in an increase in size.
This work will examine the best combination of mulch and irrigation to optimize hazelnut tree growth and yield while minimizing water waste. Our mulches include sawdust, yard compost, mint compost and biochar. Preliminary data indicate that sawdust mulch made trees less vigorous.
Berms are beneficial for tree growth in poorly drained, wet soils. They raise the roots and surrounding soil above ground level. Crops, such as blueberries, are regularly grown on berms. We will be evaluating the effects of berms on hazelnut tree growth.