[00:00.00]如果您也喜欢 恒星英语学习网 www.hxen.com 请与您的朋友分享 This is the VOA Special English [00:02.70]Agriculture Report. [00:04.65]Some trees can survive [00:07.09]a long time without water. [00:09.68]Think of trees [00:11.03]that grow in the desert. [00:12.24]But other trees may need [00:14.49]more moisture than they can get [00:16.68]from rainfall or from the air - [00:19.19]- from, say, coastal or mountain fog. [00:22.77]The soil stores moisture [00:25.71]during cooler weather. [00:26.96]But most of that moisture [00:29.30]is gone by the middle [00:31.09]or end of the hottest [00:33.08]months of the year. [00:34.52]Trees and other plants [00:37.36]can look thirsty. [00:38.46]Leaves can become droopy [00:40.79]and hang downward. [00:42.56]They can also turn yellow. [00:45.24]Yellowing can be a sign [00:47.83]of too much water. [00:49.23]But it can also be a warning [00:52.36]sign of too little water. [00:54.90]The Vacaville Tree Foundation [00:57.88]is a volunteer community group [01:00.17]in California. [01:01.27]It has advice for watering [01:03.61]newly planted trees [01:05.70]and established trees. [01:08.19]With a newly planted tree, [01:11.47]the roots have not yet spread [01:14.08]out from the root ball. [01:15.87]The root ball can become dry [01:18.42]faster than the dirt around it. [01:21.10]So put water on the area [01:23.94]of the root ball [01:25.33]and the surrounding soil [01:27.33]until the roots become established. [01:30.36]Once a tree is well established, [01:33.80]water deeply instead of often. [01:37.38]The amount of water needed [01:40.19]depends on the tree and the soil. [01:43.12]Clay soils hold water [01:46.06]for longer periods [01:47.60]while sandy soils hold less water. [01:51.59]During the hottest season, [01:54.48]a deep watering [01:56.02]may satisfy a tree for anywhere [01:59.21]from ten days to four weeks. [02:02.51]Part of skilled watering [02:05.36]is knowing to stop [02:07.30]when the soil needs a little time [02:09.70]to absorb the water. [02:11.74]Otherwise the water runs off [02:14.92]the surface and gets wasted. [02:17.21]Ted Swiecki is a plant scientist [02:21.24]in California with [02:22.73]the Phytosphere Research company [02:25.57]and the Vacaville Tree Foundation. [02:28.11]He says people should not water [02:31.85]established trees [02:33.20]at the base of the trunk. [02:35.14]This can harm the tree. [02:37.87]Too much water in the soil [02:40.61]at the base of a tree can lead [02:43.42]to the growth of fungi. [02:45.31]If the area is too wet, [02:48.29]harmful organisms have a better chance [02:51.48]to invade the tree and cause disease. [02:54.42]Mr. Swiecki says this is true [02:58.30]especially in Mediterranean [03:00.59]and semi-dry climates. [03:02.78]Many trees in these climates [03:06.00]have adapted to having a dry area [03:08.70]near their base [03:09.89]during the hottest season. [03:11.73]TED SWIECKI: "Water displaces air [03:13.18]in the soil. [03:14.12]And roots are aerobic; [03:17.16]they require oxygen (for the soil) [03:20.03]to function properly. [03:21.28]So if you keep the soil saturated [03:24.31]and there's no air there, [03:25.86]and then you are basically [03:27.25]starving the roots for oxygen." [03:29.20]And that's the VOA Special English [03:31.84]Agriculture Report, [03:33.70]written by Jerilyn Watson. [03:35.64]For more growing advice, [03:38.63]and to learn English, [03:40.91]go to www.hxen.com. [03:45.20]You can also find us on Facebook, [03:48.10]Twitter and YouTube [03:50.39]at VOA Learning English. [03:53.87]I'm Bob Doughty.如果您也喜欢 恒星英语学习网 www.hxen.com 请与您的朋友分享