2.2 | Experimental treatments and field management
This field experiment began in
2008. The site had a long history (> 40 year) of wheat and
maize double cropping rotation under the same managements before the
study, and the typical rotation of wheat (cv. Mianyang 26) and maize
(cv. Nonghua 50) was also chosen for this study. A randomized complete
block design experiment using 12.5-m-wide and 56-m-long plots was
managed over 8 years with four replicates. Three tillage methods
[control with no-tillage and straw removal (CK),
no-tillage with straw stubbles
30–40 cm in height (NT), and rotary tillage with straw incorporation
(RT)] were applied before maize planting, and two straw treatments
[straw return (SR) and no straw return (SR0)] were applied after
maize harvest. Thus, there were totally 24 plots with four replicates
for each treatment(CK-SR, CK-SR0,
NT-SR, NT-SR0, RT-SR, and RT-SR0).Both wheat and maize were harvested
using combine-harvesters.Wheat straw was manually removed from the
farmland in CK, but was remained with straw stubbles 30–40 cm in height
in NT, and was chopped into about 10 cm pieces and incorporated into the
top 10 cm soil layer immediately after harvest with ~
2-3 times of rotary tillage in RT. Maize straw was chopped into about 10
cm pieces and incorporated into the top 20 cm soil layer immediately
after harvest with ~ 2-3 times of rotary tillage in SR,
and was manually removed from theSR0 plots.
The wheat was sown at a rate of 210–225 kg ha-1yr-1 with a row spacing of 15 cm, and the maize was
planted at a density of approximately 63,000 plants
ha−1 yr-1 with a row and plant
spacing of 60 and 25 cm, respectively. The basal fertilization rates
were 120 kg N ha−1 yr-1 and 102 kg
P2O5ha−1yr−1for wheat production, and were
67.5 kg N ha−1 yr−1 and 22.5 kg
P2O5 ha−1yr−1for maize production, respectively. A rate of 120
kg N ha−1 yr−1 was also applied at
the tasseling stage of maize. Urea and diammonium phosphate provided the
required N and P2O5 in all treatments.
Before sowing wheat, ~ 2-3 times of rotary tillage were
applied at a depth of 20 cm in all the plots for the convenience of
wheat seeding. Irrigation and pesticide management practices were in
keeping with local agronomic practices.