2 February 1996

PLASTIC MULCHES SWELL PROFITS

Growing maize under plastic can speed establishment and maturity on marginal sites, as one Co Durham producer has discovered. Jonathan Riley reports

GROWING maize under plastic gains milk producer Gordon Tweddle a fortnights worth of growth. But he maintains that producing a consistent crop on a marginal site is also down to attention to detail.

Maize is normally grown in areas where Ontario maize heat units exceed 2200. But at Mr Tweddles Garthorne Farm, Darlington, Co Durham, heat units reached only 2200 for 1995 while in 1994 only 1800 units were achieved, the temperature held down by cold easterly winds.

Maize was first grown in 1990 as an experiment using LG2080 on our 6.5ha (16 acres) at Leyburn, North Yorkshire, when he had the option of reseeding a grass ley. The crop yielded 42t to 44t/ha (17t to 18t/acre) freshweight and was harvested at 30% dry matter (DM) after frost in late October.

"The next year we expanded the acreage, and also grew 15ha at Darlington, using an earlier maturing variety. We were faced with a completely different weather pattern that saw us harvest at 18% DM," says Mr Tweddle.

"The early variety needed heat which it didnt get. However, we had also drilled acre strips of Botanis and LG2080 which outperformed the early variety both in terms of maturity and DM yield.

"I would advise those considering maize to choose a main variety then put in strips of other varieties and make the choice that suits their farm," he says.

He has increased the maize area grown each year up to 100ha (250 acres) grown between the two farms in 1994 when plastic was first introduced. The cold spring and summer meant that there was a significant financial benefit from growing under plastic. This was supported by a Maize Growers Association/Nickerson Seeds study, based at Garthorne in 1994, which compared varieties grown under plastic and grown conventionally.

"I think that plastic increases the temperature around the plant enabling roots to develop during spring, even when it is cold.

Much of the 1995 maize crop was again planted under plastic.

"Under plastic we are not worried about the cold taking the plant, so we can drill earlier rather than later in mid April – but only when soil conditions are right," says Mr Tweddle.

Seed rates are below those for a more traditional maize growing site at 88,900/ha to 93,800 plants/ha (36,000 to 38,000 plants/acre) so that the establishing plant gets more light for earlier maturity.

Land is ploughed, subsoiled and two passes of the power harrow are made before a pre-emergence herbicide spray is worked in with the power harrow. Drilling then takes place when the soil temperature at a depth of 100mm (3.9in) reaches 10C.

"We need to get the seed deep enough so that it reaches the moisture level. In 1994 we drilled 4cm to 5cm deep in dry conditions under plastic and had good germination. On the advice of the drill manufacturer in 1995, we drilled shallower in good moist conditions, again under plastic. But we had poorer germination due to the seed striking and droughting off because of insufficient soil cover," he says.

While drought stress was a problem on some southern sites, cold temperatures until the end of May in Co Durham meant the crop started growing later.

In 1995 MGA/Nickerson Seeds repeated the study at Garthorne, and maize grown under plastic germinated a week after drilling. Without plastic, germination took two weeks. This early start gave a significant yield and quality advantage for plastic above conventionally grown maize.

"Even though the 1995 crop reached maturity at the same stage as in 1994, we lost two to three weeks growth at the start of the season which meant that yields were lower in 1995.

"Once the weather warmed up the plants under plastic grew quickly, whereas in bare ground it took a further 10 days to establish," says Mr Tweddle.

"But, because of the warm, dry summer, maize grown without plastic reached maturity at the same time and the benefit of using plastic does not appear to be as marked as the previous year.

"MGA members will have access to the full trial results to assess 1995 trial benefits for themselves.

"For 1996 we need to look at how we think the weather will go and whether to grow under plastic or not. A return to cooler summers will mean the benefits of plastic will increase," says Mr Tweddle.

"An emerging problem is the increased presence of black nightshade and fat hen. Because of the plastic, we rely on a pre-emergence spray of atrazine to control weeds."

Though they caused no problems in the 1995 maize crop, they may force Mr Tweddle to reduce the acreage under plastic this year to make use of post-emergence sprays. &#42