Integrated double-cropping maize technology is mature, and the North China Plain can now grow it

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On July 13, harvesting began on the 200-mu double-cropping maize demonstration plot in Lianzhu Village, Henan Tuan Town, Quzhou County, Hebei Province. "This is the earliest-harvested spring maize in Hebei Province and even in the North China region," said Chen Xinping, professor at the College of Resources and Environmental Sciences of China Agricultural University and head of the "Double-Cropping Maize Experimental Demonstration Project."

Because spring temperatures are low, spring maize in Hebei Province is generally sown in late April or early May and harvested in late August. "In recent years, as the climate has warmed, the accumulated temperature in spring in the Hebei region has increased by 260 degrees C. On this basis, we used film-mulched sowing technology to advance the sowing time of spring maize to mid-March, so that it can be harvested in mid-July," Chen Xinping explained.

　　Double-cropping maize can save 30%-50% of water

In 2012, the High-Yield and High-Efficiency Modern Agriculture Research Base (Quzhou) of China Agricultural University began conducting double-cropping maize trials, that is, exploring the replacement of the traditional "winter wheat-summer maize" planting model with "spring maize-summer maize." This trial focused on the improvement and adjustment of future planting structures in the North China region under changing climate and resource-environment conditions, and explored the establishment of an ecological conservation-oriented agriculture that can both increase yields and save water and fertilizer while allowing land to lie fallow.

The biggest problem in agricultural production in the North China region is the lack of water. Winter wheat, from sowing to harvest, must be irrigated at least three times and at most four or five times, consuming large amounts of groundwater. Some counties and districts in Hengshui City have already provided subsidies to encourage farmers to give up growing wheat and switch to other crops, in order to avoid continued groundwater overextraction. "Replacing winter wheat with spring maize requires only one to two irrigations, and summer maize sown in the rainy season in July generally needs no irrigation, so over the whole year two irrigations can be saved, and water savings can reach 30%-50%," compared Cui Zhenling, associate professor at the College of Resources and Environmental Sciences of China Agricultural University.

However, the spring maize variety in the double-cropping maize model cannot be chosen arbitrarily. After many trials, the double-cropping maize experimental demonstration project team selected the spring maize variety "Demeiya," which is widely planted in the high-latitude regions of Northeast China. This spring maize is cold-tolerant and has a short growth period; sown in mid-March and harvested in mid-July, it allows the second-season summer maize to be sown by the latest deadline in mid-July (in the Hebei region) and to mature in mid-November.

Double-cropping maize can provide a 4-month fallow period

In the traditional planting model, because the amount of summer maize straw is large, handling it is rather troublesome. In order to rush the planting of winter wheat, farmers often harvest summer maize before it is fully mature; the straw is still green and difficult to return to the field mechanically. With double-cropping maize, the amount of straw doubles, so would it not be even harder to handle?

"The double-cropping maize model can easily achieve full return of maize straw to the field," Cui Zhenling said. The spring maize "Demeiya" is suitable for dense planting, and its straw is thin and dries easily, so it can be directly mechanically crushed and returned to the field at harvest without affecting summer maize sowing; summer maize matures in mid-November, and because there is no longer a need to rush the farming season, harvest and straw return operations can wait until the straw is completely dry.

It should be noted that after the second-season maize straw is crushed, it is not plowed under but directly left as surface mulch. This is because there are 4 months of idle time after summer maize harvest and before spring maize sowing the following year. If the soil were left bare, it would cause problems such as loss of organic matter in the topsoil, reduced soil moisture, and dust. More importantly, during winter, when land productivity is at its lowest, a 4-month fallow period is achieved, restoring soil fertility on the one hand and optimizing land use on the other.

Under the double-cropping maize model, straw, which "everyone finds annoying," is transformed into an indispensable treasure for covering the soil surface and protecting farmland.

Double-cropping maize can reduce potassium fertilizer use by 50 kg K2O/hm2

Full return of double-cropping maize straw to the field can also greatly reduce potassium fertilizer use. In the Huang-Huai-Hai region, potassium fertilizer use can be reduced by 50 kg K2O/hm2, and maintaining 90 kg K2O/hm2 for the two seasons in one year is sufficient. This is because potassium in maize plants is mainly concentrated in the stalks, and straw buried in the soil can release most of the potassium in a very short time.

Reducing potassium fertilizer is of particular significance to China. "China's potassium fertilizer reserves account for only 1.6% of the global total, while its use accounts for 20% of the global total. Fluctuations in imported potassium fertilizer prices have become an important factor affecting China's fertilizer market. Full return of double-cropping maize straw to the field is an efficient potassium fertilizer substitution technology. If promoted on a large scale in the Huang-Huai-Hai region, it will help ease China's dependence on imported potassium fertilizer," said Guo Qiang, deputy general manager of the Potassium Fertilizer Business Department of Sinochem Fertilizer Co., Ltd.

Double-cropping maize can increase yield by 20%-30%

Double-cropping maize can save water, save fertilizer, and allow fallow periods, but what about its yield? Trial data from 2012-2014 at the China Agricultural University Quzhou "Double-High Base" show that under conventional water and fertilizer management, double-cropping maize yields reached as high as 1.5 tons per mu, 12% higher than high-yield farmers growing winter wheat-summer maize and 20%-30% higher than ordinary farmers.

The 200-mu double-cropping maize demonstration plot used the contracted land of Fan Changyong, Party branch secretary of Lianzhu Village. He told reporters: "This year the drought was severe, and our village's wheat harvest was not very good. But the spring maize on the demonstration plot did fairly well, yielding 650 kg per mu. Summer maize has now been sown, and the rainfall has been good these past few days, so this season's yield will be even higher."

Through processes such as film-mulched sowing to capture accumulated temperature, short-growth-period spring maize to fit the crop rotation window, crushing and mulching summer maize straw on the soil surface, and spring plowing and land preparation with deep plowing of straw, the project team achieved a clever combination in time and space of factors including water resources, climatic conditions, variety selection, mechanized operations, and conservation tillage technology, completing the technical integration of the entire double-cropping maize model. "It can be said that the double-cropping maize model is already mature and has the conditions for large-scale promotion in the North China Plain," Chen Xinping said with great confidence.

　　Reporter's Notes

Four Questions About "Double-Cropping Maize"

Each technology in the double-cropping maize planting model looks very ordinary, with nothing special about it. However, when these conventional technologies are combined scientifically and ingeniously, they create a planting model of breakthrough significance. It truly is a case of "what seems most ordinary is most extraordinary; what seems easy was in fact arduous." But after the interview, the reporter still had some points of confusion, which fortunately were explained in detail by the relevant experts.