Lysimeter results

Note that this page will be updated periodically as results come to hand. Last update 19/5/2015.

In October and November 2014, twelve lysimeters were collected from the golf course in Duvauchelle and six from farmland near Akaroa. The lysimeters were installed at the Lincoln University lysimeter facility in December 2014. During the summer 2014-2015, the lysimeters were irrigated to gradually increase their water content to field capacity - i.e. the point when any further irrigation leads to drainage from the lysimeter. This "wetting up" of the lysimeters needs to be done slowly to minimise rapid drainage though large pores (preferential flow) caused by unnaturally high loadings of water. During this time any mineral nitrogen that is released due to soil disturbance during installation is leached out of the system. The treatments were started on the 28th of April 2015. The chemistry of the effluent is shown in the table below.

pH9.4
NH4+ (mg/L)0.72 (0.00)
NO3- (mg/L)34 (0)
NO2- (mg/L)0.86 (0.05)
Ca (mg/L)34 (1)
K (mg/L)16 (0)
Mg (mg/L)15 (0)
Na (mg/L)92 (1)
P (mg/L)6.1 (0.4)
S (mg/L)13 (0)

Of note are the elevated concentrations of nitrate (NO3-) phosphorous (P) and sulphur (S). These are beneficial plant nutrients, but can also be problematic if they enter waterways. We will monitor the drainage for these elements, particularly nitrate, which is most likely to leach. The concentrations of heavy metals in the effluent are all below the New Zealand drinking water standards (data not shown). The Salt Accumulation Ratio (SAR) for the leachate is 18, which indicates that continual irrigation may lead to aggregate instability unless gypsum is added occasionally.

The drainage from the lysimeters is shown in the figure below. Initial results indicate no problems with infiltration or drainage of the effluents, even at the highest application rate (2000 mm / year). However, we anticipate that this high rate will result in aggregate instability and infiltration problems at some point in the two-year experiment.

Lysimeter data
Cumulative drainage from the lysimeters taken from Banks Peninsula. Each point represents the average of three lysimeters. The error bars represent the standard error of the mean.