The root hole of a toppled tree is one such source.

倾倒的树木的树根洞就是这样一个地方。

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By extending the planting hole and improving the soil, soil is humificated from root around to all orchard and then these are the base for increasing the orange quality and tree vigor.

通过扩穴改土，由根际局部熟化到全园熟化，同时增施磷钾肥，可为提高柑桔品质，加快形成丰产稳产的强健树势打下良好的基础。

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The bored hole conduced the new root bourgeoning and vegetating.

钻孔孔隙有助于萌发新根，促进根尖生长；

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One morning in September 1940, a boy called Marcel Ravidat was exploring the hills above Montignac when his dog, Robot, uncovered a hole beneath a tree root leading to a cave.

BBC: The perfect trip: Dordogne