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Weeds were not a major problem during the entire growing season of the experiment except in H5 after the winter season. These were winter weeds, which were influenced by the combined effects of both the main and the sub treatments over time. Lanyon and Griffith (1988), and Douglas (1986) expressed concerns that high applications of N and lime on lucerne stands may promote weed growth. Nevetheless, the weed compostion on the +N and limed plots were less in this experiment compared with the 0N and LPS plots. This could have been the result of no grazing during the winter period because it was a cut-and-carry system. Moot et al. (2003) state that grazing lucerne stands in winter controls weeds. However, further research could be needed in this area, especillay during wet seasons as this experiment was conducted during a mild winter. Also most weeds came from the control plots in this experiment, contradicting literature report concerns of Douglas (1986), and Lanyon and Griffith (1988).

4.10.3 Climate

4.10.3.1 Rainfall and temperature

Compared with the long term average rainfall and temperature ranges, this experimental year was conducive for high lucerne growth and productivity. The experimental period (15 months) received a total rainfall of 1070 mm, compared with the long term total annual mean rainfall of 633 mm. This 1070 mm was a result of a total monthly rainfall range of 25-250 mm over the experimental year whereas the long term yearly mean monthly rainfall range was 40-60 mm. This implies that some of the months were fairly dry with a mean daily rainfall distribution of 1- 8 mm during the project. The drier days observed were from December 2012 to February 2013 and then from July to September 2013. The highest total monthly rainfall of around 250 mm was experienced in June followed by 125 mm in May 2013. The total daily rainfall during the two springs (2012/2013) of the experimental period ranged at 25-90 mm. The temperature of the experimental period was slightly warmer. For example, the maximum temperature range during the winter period of the experiment was 14-21 °C while the overall long term mean was 11-20

°C. Thus, this was a mild winter and a mild year in general. Wynn-Williams (1982) stated that such temperature ranges of around 14-25 °C are usually experienced during spring for optimum seed germination and plant growth in NZ. Douglas et al. (1987) add that lucerne survives and produces well in drier environments with an annual rainfall range of 300-800 mm. The higher yields observed on the dryland lucerne stand in this study could be the result of the warmer year with the total rainfall of 1070 mm over the experimental period.

4.10.3.2 Soil moisture and soil water

The soil moisture % was 15-34% at 0-25cm soil depth, while it was 8-26% at 25-185 cm. They were lower than 17-54% soil moisture recorded at deeper soil profiles (185-225 cm). The overall soil moisture range was equivalent to a total soil water range of 309-644 mm. There could have been a band of gravel materials at the middle layer of the soil (25-185 cm). This could have led to higher drainage and low soil water at that depth. The opposite could have been true for the lower layer compared with the upper layers. In other words, the deeper profile could have been consist of clay pans, with high soil water compared with the upper soil depths. Lucerne, being deep tap rooted could have drawn water from that depth. Generally the moisture levels from 0-25 and 180-225 cm were at optimum to high (15-40%), whereas the moisture levels fell to as low as 8% at 25-180 cm between March and December 2013. However, the soil water levels of the individual plots in this experiment could have been variable because this data were collected from the adjacent larger lucerne plots from around 2-8 soil moisture probe tubes.

Wynn-Williams (1982) states that soil moisture levels of around 15-24% are usually experienced during spring, which are optimum for plant growth and productivity. Thus, the moisture level at the top 0-25 cm depth was adequate for lucerne growth and production. However, it was difficult to understand the soil moisture status of the soil from September 2012 and February 2013 because no soil moisture readings were taken during this period of the experiment. The daily rainfall range during this period was around 1-8 mm and a soil moisture deficit stress was obvious on the lucerne and the weeds. It was observed that the lucerne plants turned darker to paler green regardless of the 0/+ N treatments. Consequently, they started flowering at 15-20 cm height in January 2013. Even the fibrous and shallow rooted weeds on the weed plot wilted and

died while those deeper tap-rooted plants such as dandelion and dock survived during this time of the year (Figure 4.9).

Fig. 4.9 Only deep rooted weeds survived on the weed plot (left) while lucerne were already flowering at 15-20 cm heights (right) in January 2013 because of soil moisture deficit stress

Therefore, such soil moisture and the mild year could have triggered the higher yields from this experiment as lucerne thrives under such harsh conditions. Lucerne thrives well under drier conditions, but high soil moisture resulting from prolonged wet season causes a decline in growth and production (Dunbier et al., 1982). Brown et al. (2005) supported that lucerne persistency was 94% on dryland and was reduced by 49% on irrigated fields in the sixth year of their experiment in the Canterbury Plains of NZ. Thus, findings of this experiment signifies that

the dryland lucerne can perform exceptionally well, resulting in high DM yields than expected when the right environmental conditions strike. This was similar to that seen by Brown et al.

(2000) and could be a habit of dryland lucerne. D. Moot (pers. comm., October 20, 2014) further explained that when the site soil was totally full during winter, it had around 650 mm of soil water. Around 50% of this was freely available so it could have been drying out during summer and autumn when the total soil water was 325 mm, but not completely dry. He further explained that around April 2013, the soil was at its driest, which was about the lower limit of soil water. The lucerne stand might have got water stressed towards the end of their growth during this time. After April, it rained so the water recharged back to the drained upper limit of around 650 mm and the lucerne stands were picking up their growth again. Therefore, at no stage, soil water was limiting growth in the second spring because the soil water only dropped to about 580 mm. He concludes that the soil water shows the crop was actively growing most of the time, resulting in the high yields.