Twenty-Years of Hop Irrigation by Flooding the Inter-Row Did Not Cause a Gradient along the Row in Soil Properties, Plant Elemental Composition and Dry Matter Yield
In hops (Humulus lupulus L.), irrigation by flooding the inter-row can carry away suspended
particles and minerals, causing gradients in soil fertility. The effect of more than 20 years of flooding
irrigation on soil and plants was evaluated in two hop fields by measuring soil and plant variables
in multiple points along the rows. In a second experiment 1000 kg ha1 of lime was applied and
incorporated into the soil to assess whether liming could moderate any gradient created by the
irrigation. At different sampling points along the rows, significant differences were recorded in soil
properties, plant elemental composition and dry matter yield, but this was not found to exist over a
continuous gradient. The variations in cone yield were over 50% when different sampling points
were compared. However, this difference cannot be attributed to the effect of irrigation, but rather
to an erratic spatial variation in some of the soil constituents, such as sand, silt and clay. Flooding
irrigation and frequent soil tillage resulted in lower porosity and higher soil bulk density in the
0.0–0.10 m soil layer in comparison to the 0.10–0.20 m layer. In turn, porosity and bulk density were
respectively positively and negatively associated with crop productivity. Thus, irrigation and soil
tillage may have damaged the soil condition but did not create any gradient along the row. The
ridge appeared to provide an important pool of nutrients, probably caused by mass flow due to the
evaporation from it and a regular supply of irrigation water to the inter-row. Liming raised the soil
pH slightly, but had a relevant effect on neither soil nor plants, perhaps because of the small amounts
of lime applied.
The authors are grateful to the Foundation for Science and Technology (FCT, Portugal)
for financial support from national funds FCT/MCTES, to CIMO (UIDB/AGR/00690/2020) and for
Sandra Afonso’s doctoral scholarship (BD/116593/2016).
