Evaluation of the Potential of Diquat (1,1′-Ethylene-2,2′-bipyridyl) to Assist Maize Mechanical Harvesting As a Desiccant

The proportion of maize mechanical harvesting in China is still at a low level although mechanical harvesting has been widely used in the cultivation of other crops. A major reason is that the moisture content of maize kernels at the harvest stage is often too high for mechanical harvesting due to a short dehydration time window, which is caused by a wide use of double- or even multiple-cropping systems in many areas. To investigate whether diquat (1,1′-ethylene-2,2′-bipyridyl) could be used in assisting maize mechanical harvesting as a crop desiccant, a two-year field experiment was conducted in 2016 and 2017 at the Wuqiao Experimental Station of China Agricultural University by using maize hybrids, Zhengdan 958 (ZD958) and Xianyu 335 (XY335), both widely cultivated in China. Four concentrations of diquat at 0, 100, 200, and 400 mg kg–1 (equivalent to 45, 90, and 180 g a.i. ha–1) were applied at the R5 (kernel dent) stage, and the effects of diquat on kernel dehydration dynamics, grain yield, grain nutrient quality, and the residues were analyzed. The results showed that diquat at all concentrations accelerated maize dehydration. Kernel moisture content was reduced by 2.37%, 2.01%, and 2.44%, respectively. The kernel moisture loss curve follows an "S"-shaped curve and could be simulated by a logistic equation. After diquat application, grain yield, yield components, starch contents, protein contents, and oil contents were not changed (P < 0.05). The residues of diquat in maize kernels treated with the three concentrations all met the China and EU residue limits. The results indicated that diquat concentration from 100 to 200 mg kg–1 could be used to accelerate maize dehydration efficiently and safely. The parameters derived from the logistic equations of moisture loss could well-indicate the character of dehydration dynamics and could be used to accurately evaluate or compare the dehydration effects of chemicals.