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This experiment was conducted to characterise broom seed germination once dormancy wears off by sowing seeds treated with various scarification methods at several depths in the field. The results obtained from these experiments were used to design the seed- sowing experiments presented later (Chapters 3 and 4).

Seed collection and processing

The broom seeds used for this experiment were collected in November 2007 from soil samples from a broom-invaded Eucalyptus spp. plantation (40°23'S and 175°37'E) at the

soil samples were stored in a cool room at 5oC for several days, extracted, and stored as before.

Laboratory experiment

This experiment was conducted to assess the germinability of broom seeds under various scarification treatments to see how well the seeds germinate once the seed coat has been broken. The experiment involved the following seed treatments (Fig. 2.3): (1)Hand scarification: seeds were stored moist in a growth chamber at 15°C overnight

to soften the seed coat followed by nicking each seed with a scalpel.

(2) Mechanical scarification: seeds were abraded with P100 grade sandpaper placed in

the drum of a Forsberg scarifier and rotated for 20 seconds. The rotating time used here was selected as it had previously been shown to give the highest number of germinated seeds in a pilot study testing the effects of time of scarification (0, 5, 10, 15, 20, 25 and 30 seconds) on seed germination (data not shown).

(3) Untreated control: seeds were left unscarified as controls.

Following the treatment, the seeds were placed in plastic boxes (17 cm × 12 cm wide and 5 cm deep) on a 25-grid double-layer filter paper and moistened with distilled water. Each box contained 50 seeds (two seeds per cell) with four replicates for each treatment (200 seeds per treatment). The boxes were kept in a growth chamber that maintained 16 hours light at 30°C and 8 hours darkness at 20°C (Don 2006). Distilled water was added regularly (daily) to simulate the periodic wetting and drying experienced by seeds in the field.

Seed germination was monitored weekly and the number of germinants counted and their condition recorded as normal or abnormal and then they were removed from the boxes. Germination was recorded when the radical was 2 mm in length or had perforated the teguments. Mouldy seeds were recorded as dead and removed. Final counts were made after 42 days when all remaining ungerminated seeds were classified as being dead, hard or fresh but ungerminated.

A

B

Figure 2.3. Methods of scarification applied for broom seeds: (A) hand scarification and (B) Forsberg scarifier.

Field experiment

Based on the results of the laboratory experiment, a seedling emergence field experiment was conducted to determine the effect of scarification and burial depth on broom seedling emergence. A pasture plot with no history of broom invasion was established at the Fruit Crop Unit (40°23'S, 175°36'E), Massey University, Palmerston North on 29 January 2008 in which seeds were planted at varied depths.

Average monthly temperature and rainfall during the time of the experiment (collected by the Grasslands AgResearch weather station approximately 0.5 km away from the study site) are shown in Fig. 2.4. The maximum daily temperature ranged from 22.6°C in January to 11.8°C in June.

Aug 07 Sep 07 Oct 07 Nov

07

Dec

07

Jan 08 Feb 08 Mar 08 Apr 08 May 08 Jun 08 Jul 08 Aug 08 Sep 08 Oct 08 Nov

08

Dec

08

Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jun 09 Jul 09 Aug 09 Sep 09 Oct 09

Rainfall (mm) 0 50 100 150 200 250 Temperature (°C) 0 5 10 15 20 25 Rainfall Tmax Tmin

Figure 2.4.Mean total monthly rainfall (mm) and mean monthly maximum (Tmax) and minimum (Tmin) temperature (°C) over the duration of the two experiments. The arrows show the time when each experiment started in January 2008 (Experiment 2.2.2) and September 2007 (Experiment 2.2.3).

The soil was a Manawatu fine sandy loam and samples taken from the trial site had an average pH of 6.1. Olsen-P was measured at 56 μg mL–1 and the Na, Mg, K and Ca levels averaged 0.15, 1.14, 0.77 and 8.9 me 100 g–1, respectively. Soil organic matter averaged 5.3% and average CEC was 14 me 100 g–1.

Before the start of the experiment, the site was tilled and any residual vegetation removed using glyphosate (Roundup Transorb at 7 ml L–1). The broom seeds (50 seeds per treatment) used were from the same source as the laboratory experiment. Two factors varied: (1) seed scarification (three groups: hand-scarified, Forsberg machine- scarified (for 20 seconds) and non-scarified); and (2) sowing depth (three levels: at soil surface, 1 and 2 cm underground). A total of nine (3 × 3) combinations were tested in five replicate blocks (250 seeds per treatment). The experimental units consisted of galvanised steel cylinders (15 cm diameter; 10 cm height) buried 8 cm in the soil to preventing the seeds being lost from water flooding (Figs. 2.5 and 2.6), each of which contained 50 seeds. A fine chicken-wire mesh cage covered with a bird nest was placed on each block (Fig. 2.6). After sowing, the soil was irrigated regularly over the first several weeks to ensure germinating seedlings were not water stressed.

Data collection

The broom seedlings that emerged in each treatment were removed and recorded weekly for the first couple of months and later every two weeks. A 20™20 cm acetate sheet was used to record the position of each seedling (Fig. 2.6). The experiment ran for 18 months during which all vegetation presented in the subplots was regularly removed using scissors.

U0 S0 H1 S2 C U1 H0 S1 H2 U2 Block 5 Block 1 Block 2 Block 4 Block 3

H – Hand-scarified seeds U – Unscarified seeds

S – Forsberg scarifier seeds C – Control (unsown subplot) 0, 1, 2 – Sowing depths (cm) – Cage covered with bird nets