center of each soil bin. A treatment without cover and tillage was used
as a control to simulate the standard local management practice (NC,
no cover and no natural vegetation). The other 4 treatments were:
(i) Full ground mulching (200 cm × 80 cm, 100%) with jujube branch
(BM), (ii) Strip (60 cm × 80 cm strip at both ends of the soil bin, 60%)
shallow tillage (ST) to 8–10 cm soil depth, (iii) Jujube branch mulch beneath
the tree canopy (80 cm × 80 cm around the jujube tree's trunk,
40%) + strip shallow tillage (BMT), (iv) Jujube branches mulch beneath
the tree canopy + strip white clover cover (BMWC). The detailed layouts
of the five treatments are shown in Fig. 2.
Three-year-old jujube trees from Qingjian County with a mean
initial height of 24.5 ± 4.4 cm were transplanted on November 20th,
2009. The mulch used consisted of jujube branches cut into 5–8 cm
long segments and uniformly applied to the soil surface to a thickness
of approximately 5 cm on May 1st, 2010. White clover (Trifolium repens
L.), widely planted on the Chinese Loess Plateau, was used as a cover
crop and seeded at a rate of 15 g m−2 on March 5th, 2011. White clover
was allowed to wither and die naturally without mowing, and the litter
remained on the soil surface. It would regenerate from roots in the next
growing season. Urea (55 g m−2
) was applied with water onto each plot
in June 2012. For the tillage management, a rake was used to manually
till the soil surfaces to a depth of around 8–10 cm every 2 rainfall events