2.2. Experimental design and treatments
A field experiment was conducted at the experimental station of the
Department of Agricultural and Environmental Chemistry, University of
Agriculture in Krakow (50°04′ N, 19°51′ E, 280 m a.s.l.) in the period
from 2014‑2018. The climate of the experimental site, which is situated
in southern Poland, is considered temperate. The average annual
temperature during the study period was 9.7 °C, and the average annual
precipitation was 639 mm (Figure 1). The soil in the experimental field
was a Eutric Cambisol (loamy sand) (IUSS Working Group WRB, 2015). Table
2 lists the soil characteristics based on the samples collected in 2014
before the start of the trial.
The straw and biochar were applied on March 2014. The soil amendments
were mixed with the soil using a rotary harrow at a depth of 10 cm.
After the amendment application, the seeds of the red clover/grass
mixture were sown at a seeding rate of 60 kg ha-1; the
mixture included perennial ryegrass (L. perenne L.) cv. Victorian
(with a 20% rate in mixture) and cv. Solen (20%), timothy
(Phleum pratense L.) cv. Erecta (15%), meadow fescue
(Festuca pratensis Huds.) cv. Ardeinia (10%), tall fescue
(F. arundinacea Schreb.) cv. Alix (10%), Italian ryegrass
(L. multiflorum L.) cv. Gaza (10%), Westerwolds ryegrass
(L. westerwoldicum Breakw.) cv. Mowester (10%), and red clover
(Trifolium pratense L.) cv. Dajana (5%).
The field experiment consisted of 24 plots areas of 1
m2. The experiment was established as a randomized
block design with three replications. The following treatments were
applied: wheat straw at a rate of 5 t ha-1 (WS),
miscanthus straw at a rate of 5 t ha-1 (MS), wheat
biochar at a rate of 5 t ha-1 (WBH), wheat biochar at
a rate of 2.25 t ha-1 (WBL), miscanthus biochar at a
rate of 5 t ha-1 (MBH), and miscanthus biochar at a
rate of 2.25 t ha-1 (MBL). A treatment with mineral
fertilizer but without organic amendments (MCTR) was used, and a control
treatment (CTR) without mineral fertilizer and without any amendments
was also tested. The mineral fertilizer was applied every year at rates
of 100 kg N ha-1, 40 kg P ha-1 and
120 kg K ha-1.