Response of maize yield and soil nitrate to deep plowing and straw return in saline-alkali soil

Objectives Saline alkali soil is important farmland resource in our country. To search for suitable tillage and amount of straw return in order to improve soil fertility and maize yield in saline-alkali soil.

Methods A field experiment was conducted for 4 consecutive years from 2014 to 2017 in Wudi County, Binzhou City, Shandong Province. Saline-alkali soil was common in this region, and summer maize was the test crop. The main treatment factor was tillage: only rotary tillage at 15 cm deep in summer (R) in half of the experimental plot, and further loosing 35 cm deep after rotary tillage (S) in the other half part. The sub treatments were two winter wheat straw returning amounts: half and full of the wheat straws (3350 and 6700 kg/hm²) were returned into soil before sowing of maize (B and Q), and no straw returning was used as the control. The total nutrients inputs of all treatments were the same. Plant dry matter and nitrate reductase in ear leaves were measured every 10 days from anthesis to harvest stage. At V9, flowering and harvest stages of maize, soil samples were taken in 0–100 cm layer with intervals of 10 cm, and nitrate nitrogen content was measured.

Results There was no significant difference in dry matter accumulation and yield between the two tillage treatments in all growth stages with the same straw returning. Compared with the half straw returning, the dry matter accumulation under full straw return was less before flowering stage, but caught up at the flowering stage, and became significantly higher at harvest, with an increase of 8.6%–9.7% in four years (P < 0.05). The four years’dry matter accumulation in SQ treatment was increased by 2.5%–7.3%, 1.6%–4.2% and 7.6%–20.3%, compared with SB, RQ and RB (P < 0.05). There was a significant and positive interaction between the deep tillage and the full straw returning, and the combination of the full straw returning and the deep tillage was conducive to the improvement of grain yield, which was significantly different from other treatments (P < 0.05). In the four years, the average nitrate nitrogen contents in the RQ and SQ were lower than those in the SB and RB at V9 stage, and similar at flowering stage, significantly lower at harvest, with the average nitrate nitrogen accumulation decreased by 17.9% (P < 0.05). In 4 years, the average nitrate nitrogen accumulation of subsoiling treatments in 0–100 cm layer was 8.9% lower than those of mere rotary tillage treatments(P < 0.05).

Conclusions In the saline-alkali soil, the combination of straw returning and subsoil plowing has a positive interaction on yield increasing of maize. The effect of full straw return combined with shallow rotary and subsoiling could further improve the maize yield and decrease the accumulation of nitrate nitrogen in the soil.