Soil health for sugar

New sugar cane varieties increase yield, but the long-term impact on the soil is untested. Richard Cole started leaving crop residue on the soil nine years ago and so far yield is higher and he’s avoiding eldana infestations. Robyn Joubert reports.

- Advertisement -

New sugar cane varieties increase yield, but the long-term impact on the soil is untested. Richard Cole started leaving crop residue on the soil nine years ago and so far yield is higher and he’s avoiding eldana infestations. Robyn Joubert reports.

About nine years ago Hibberdene cane farmer Richard Cole found himself with his back against a wall. He was faced with declining yields, eldana infestations and unhealthy soil. At the same time sugar prices were low and input costs were rising, stripping his farm of profitability. And in a classic case of fight or flight, Richard came out of his corner boxing.

Along with three other farmers in the area, John Grant, Peter Richards and Rod Norton, he came to the conclusion that the soil had been impoverished by long-term monoculture and had little organic matter, trace elements or microbial activity left. “We looked at the burning versus trashing issue and decided to take the huge step of moving to green cane harvesting – no more burning before harvesting. Our aim was to maximise yield in a sustainable manner and produce healthy sugarcane with a high sucrose content, ” he says.

- Advertisement -

To help ease the transition for the cutters from burnt to green cane Richard built in a productivity coefficient. “The cutters would be cutting less green cane than the burnt cane they had been cutting, so I was prepared to pay a slight premium. At the end of the day they needed to earn roughly the same, if not more than they were earning before,” he says. Richard has a very stable workforce who cut and stacked on average 3,2t/worker/day during the last season. “The top guys cut an average of over 4t. About a third of the cutters achieve above 3,5t/worker and a third between 3t and 3,5t. The weak cutters are below that level,” he says.

The trash blanket

Since leaving crop residue (a trash blanket) on the soil, Richard has noticed increased soil organic content, increased microorganism activity and increased numbers of earthworms. He has also reduced his herbicide use. “The trash blanket does a lot to suppress weeds. As the organic matter levels built up I used less herbicide,” he explains. he trash blanket mulch is worth an extra 100mm of rainfall per annum in terms of moisture retention (9t/ha yield benefit). “During this drought period, the cane stresses two weeks later than on the burnt fields. The trash blanket also protects the soil from raindrop spatter, making more effective use of rainfall as it filters through the trash into the soil rather than running off,” he explains.

CMS and lime

While trashing is at the heart of Richard’s drive to improve soil health and yield, he’s using a multi-faceted approach. Five years ago he stopped using Limestone Ammonium Nitrate (LAN) in favour of Condensed Molasses Stillage (CMS). CMS is high in nutrients, particularly potassium, and can be applied to cane fields as a liquid fertiliser. “We’re very happy with the results and are experimenting with potassium (K), phosphorus (P), and nitrogen (N) levels. But it’s all long-term stuff,” he says. Richard keeps application rates constant at 2 600ℓ of CMS/ha – but spikes it or orders specific ratios of N:P:K to suit individual fields. “We buy the CMS field-ready. From a practical point of view, the crews get into a routine and you want to keep the application rate constant,” he explains.

Another change was to correct the soil pH by using a liming programme. “The big challenge for me was to get the lime down into the subsoil in a way that will disturb the soil as little as possible. Gypsum is the best medium, but we don’t have the equipment to handle it, so we use pool agricultural lime. Our terrain is not suitable for a lot of infield work with machines,” he explains. Doing their bit to get the lime down to the subsoil where it’s needed, are the fat glistening earthworms.

“Earthworms are my ploughs,” says Richard. “They turn the land over by burrowing into the soil and creating channels. When it rains, the water runs through the channels taking the stool roots deeper and the lime down to the subsoil.” The liming programme is a long-term one with application rates for all fields ranging from 2t/ha to 4t/ha depending on recommendations of the soil analysis. This year Richard plans to go back and resample the subsoil of the fields he planted five years ago to see how far down the soil profile the lime has travelled.

Managing eldana through nitrogen

Richard wanted to manage his eldana problem with better soil health rather than with chemicals. “If you look at the big picture, with healthier soil you will have healthier plants that are less susceptible to disease,” he says. According to his records in November 2002 he had an average of 15 eldana per 100 stalks. In October 2005 it was 22,3 eldana per 100 stalks and 18,5 eldana per 100 stalks in November 2006. By December 2007 eldana populations had plummeted to 3,8 eldana per 100 stalks and kept on dropping. “Right now eldana levels are very low. We attribute this to the climate and we’ve also lowered the amount of nitrogen we put down. The flip side of lower nitrogen is that you get lower yields, but this is somewhat compensated for by the new cane varieties that bump up sucrose levels. It is a balancing act,” he says.

Dirk McElligott, South African Sugar Research Institute extension officer says that over the past few years there has been a decline in eldana infestation in the Hibberdene coastal ward area. He says it averages to about 5,63 eldana per 100 stalks, with Richard’s Ashbrook farm at about 2,91 eldana per 100 stalks for the 2007 season. Since Richard started his “green” approach to replenishing the soil, he has had good years and bad, but generally his yield has been in the mid 80t/ha over a 12-month to 14-month ratoon cycle. “We haven’t dropped below 80t/ha and have been above 90t/ha once. Our best year was 2002 with 92t/ha and that after only two or three years into the new programme. In 2003 the average yield was 81t/ha, in 2004 and 2005 it was 87t/ha, in 2006 it was 85t/ha and in 2007 it was 81t/ha. That’s just how it goes,” he says.

Above the curve

When farming for profit, growers look at the recoverable value (RV) yield. This is worked out in terms of tons of sucrose that can be produced per hectare. Since 2000 Richard has achieved an average of 9,3t RV per hectare. “Growers in the Hibberdene North area are averaging 9,2t RV per hectare. The average RV yields for the Sezela coastal growers since 2000 amounts to about 7,48t RV per hectare. Richard is achieving 1,82t RV per hectare more than the average coastal grower. At the current RV price of R1 691,12/ton RV, Richard is grossing R3 077,83/ha more than the average coastal growers,” says Dirk.

Richard describes his method of farming as a hybrid approach. “We take a soft approach to the land where it’s feasible. There is no getting around using herbicides and fertiliser, but we try to use soft herbicides at lower rates and don’t spray full cover spray, rather part cover where it’s necessary. That is why our herbicides costs are lower,” says Richard. The path he’s treading isn’t easy or cheap. “But there is no comparison between the condition of the soil now and when we started. It smells so good you want to eat it,” he says. Contact Richard Cole on 039 699 3191 or e-mail [email protected]

A sunn hemp and trash blanket trial

When Farmer’s Weekly interviewed Richard in 2004 he was running trials with sunn hemp as a green manure rotational crop in fallow fields prior to replanting sugarcane. For two years now he has been running another trial growing sunn hemp when the field is fallow and then leaving a trash blanket after he replanted sugarcane. Sunn hemp grows rapidly in a relatively short growing season and increases soil organic matter, fixes large amounts of nitrogen and reduces nematode infestation. “We originally planted dry beans in the fallow field for a few years,” Richard recalls. “Then we planted sunn hemp for a few years.”

While Richard had good results with sunn hemp, he was put off by the increased traffic through the field. “Planting and harvesting sunn hemp means a lot more machines through the field. We had to disc the field, plant the sunn hemp, roll it, and then either slash it down or disc it again when it was at 60% flowering stage,” he says. “We’re trying to have as little traffic and work the soil as little as possible to minimise compaction.” The crop is cut and the trash blanket left intact on the field and the old crop killed with Roundup. “The problem is that because we aren’t working the soil, the lime is sitting on top. Where the terrain allows I might disc it once, which also cuts up the trash blanket,” he says.

Managing eldana

Climate is one of the major factors influencing eldana populations. The drier the conditions, the more stressed the cane and the higher the eldana infestation. “To control eldana at acceptable levels, an integrated pest management programme (IPM) needs to be implemented,” says South African Sugar Research Institute extension officer Dirk McElligott. “Moisture stress should be minimised with conservation practices such as trashing and implementing surface-water management plans. One also needs to retain wetland and flood plain areas in their natural state, allowing the eldana to move back into its natural sedge habitats,” he says. Dirk says farmers should also plant “push-pull” crops such as Melinis grass that “pushes” eldana away from the sugarcane and back to the sedges, and “pull” crops such as Bt1 Maize or buckwheat, which can be planted in waterways to attract predators that feed off eldana.

“Part of the IPM programme is to reduce the harvesting age of cane, as eldana levels increase dramatically in ratoon cane older than 15 months. Planting the right varieties of cane according to specific soil types will also minimise eldana infection. Nitrogen management is also very important,” says Dirk. While a healthy plant is less vulnerable to pests and disease, a healthy plant with high nitrogen levels will still attract eldana. “Although not practiced widely on the South Coast, spraying the pesticide Fastac is one of the management practices used in the IPM programme. Unfortunately to control eldana in an area, all growers need to adopt an IPM programme as one farm could harbour the pest, which will then always be a threat to neighbouring growers,” says Dirk.