*2.1. Plant Material and Location of the Experiment*

The field experiment was carried out in the years 2006–2008 at Kruszyn Krajenski near Bydgoszcz (central Poland) on a sandy soil (Figure 1).

The soil was classified to Typic Hapludolls. The clay content in the topsoil was 7% and, in the subsoil, the clay content ranged from 3% to 5%. The average organic matter content was 1.19%. The water reserve to 1 m depth of soil at field capacity was 87 mm and the available water was 68 mm. The field experiment was conducted in a randomized block design of a 2-factorial "split-plot" system with 4 replications. The first factor was irrigation used in 2 variants: O–non-irrigated plots (control) and D–drip-irrigated plots. The second factor was 13 American's cultivars asparagus (*Asparagus officinalis* L.) including Jersey Giant, Jersey Knight, Jersey Supreme, Jersey Deluxe, Jersey King, Atlas, Grande, Apollo, Purple Passion, UC 157, NJ 953, UC 115, and JWC 1. The asparagus crowns were planted 10th of April 2003.

Terms of single irrigation treatments of asparagus were determined on the basis of tensiometer indications according to Horticultural Institut in Geisenheim (Germany) [17]. During the irrigation season, the soil water potential was not less than −50 kPa. The surface drip irrigation of asparagus plants performed done using 16 mm diameter linear drip line T-Tape, with a 20 cm distance between the emitters. The flow rate was5lm−<sup>1</sup> h<sup>−</sup>1.

**Figure 1.** Location of the Bydgoszcz region—within the Kuyavian-Pomeranian Province—in Poland and in Europe.

The standard growing techniques as recommended for asparagus under Polish conditions according to Knaflewski [1] were applied. The asparagus was cultivated for green spears. The plot area for harvest was 15.12 m2 (24 pcs × 35 cm × 180 cm). Green spears were daily collected for 9 (2007) or 10 weeks (2008) depending on the year of harvest. The observation included both summer stalks in the years 2006–2007 and green consuming spears in the years 2007–2008. The following evaluations were made: Height (cm), number, and diameter (mm) of summer stalks, as well as marketable yield (t·ha<sup>−</sup>1), weight (g), and number of green spears. The irrigation water use efficiency (IWUE) was also calculated, which is the quotient of the increase in yield obtained during irrigation and the seasonal dose of water used during irrigation. Irrigation water use efficiency (kg·ha−1·mm−1), which presents the effectiveness of water use, was calculated for a marketable yield of green spears using the following Equation (1):

$$\text{IWUE} = \frac{(\mathbf{y} - \mathbf{a})}{\mathbf{x}} , \tag{1}$$

where

y = yield after irrigation (kg),

a = yield without irrigation (kg),

x = seasonal dose of water used in irrigation (mm).

The experimental data height, number, and diameter of summer stalks, as well marketable yield, weight, and number of green spears were statistically processed by variation analysis. Mean values were verified with Tukey's test at a 5% level.
