Cover crops – Part 2 of 3: Elim­i­nate weeds and re­duce fer­tiliser use

Im­prov­ing and main­tain­ing soil health is not an overnight fix, but a life­long en­deav­our that re­quires patience and ex­per­i­men­ta­tion. In this sec­ond part of a three-part se­ries on cover crops and soil health, US farmer and cover crops coach Steve Groff shar

Farmer's Weekly (South Africa) - - Contents -

As­pi­rant and ex­ist­ing con­ser­va­tion agri­cul­ture farm­ers need to ap­pre­ci­ate that im­prov­ing and main­tain­ing good soil health is a never-end­ing process. Dur­ing this life­long jour­ney, there will be times when they ex­pe­ri­ence hur­dles and fail­ures in their con­ser­va­tion agri­cul­ture ac­tions. In­stead of throw­ing in the towel, they should un­der­stand that ev­ery set­back is tem­po­rary and, with re­search and per­sis­tence, can be over­come. So says US farmer and cover crops coach Steve Groff.

“I’ve been prac­tis­ing con­ser­va­tion agri­cul­ture for 35 years. It’s a long time. As long as I’m alive, I ex­pect to be con­stantly learning in my jour­ney of achiev­ing and main­tain­ing good soil health on my farm.

“Nowa­days, even if my farm has heavy rain, there’s very lit­tle run-off, no ero­sion, and high mois­ture in­fil­tra­tion. This is due to soil cover and the con­stant pres­ence of liv­ing plants on my fields. But when I first started with no-till and cover crops, it took me a num­ber of years to achieve th­ese ben­e­fits.”

Groff urges farm­ers to go out to their lands when it rains to per­son­ally ob­serve whether the soil is cap­tur­ing the rain­wa­ter rather than al­low­ing it to run off, tak­ing top­soil, nu­tri­ents and mois­ture with it.

her­bi­cide re­sis­tance

A pro­lif­er­a­tion of weeds re­sis­tant to her­bi­cides, par­tic­u­larly glyphosate-based prod­ucts, has been ob­served in many coun­tries, in­clud­ing South Africa. This wor­ry­ing phe­nom­e­non poses a threat to food se­cu­rity.

Fast Facts

• Im­prov­ing and main­tain­ing good soil health is a life­long learning process of both fail­ures and suc­cesses. • S horter-sea­son cash crop ge­net­ics can be used to ex­tend the cover crop pro­duc­tion sea­son and biomass. • Once the cover crop is dead, its residue on the soil sur­face will con­tinue to sup­press weed growth. Groff gives the as­sur­ance, how­ever, that, with good man­age­ment, cover crops can help rid crop­lands of her­bi­cidere­sis­tant weeds.

“Cover crops don’t nec­es­sar­ily elim­i­nate the need for her­bi­cides to con­trol weeds, although this is pos­si­ble. Cover crops and crop residues on the soil sur­face can, how­ever, sig­nif­i­cantly sup­press weed growth. The con­stant, longterm use of cover crops and crop residues leads to everdi­min­ish­ing num­bers of weeds, in­clud­ing her­bi­cidere­sis­tant types, that are able to ger­mi­nate and go to seed. This means that, even­tu­ally, any re­main­ing her­bi­cide-re­sis­tant weed ge­net­ics con­tinue to be sup­pressed in a land.”

In the US, stool­ing rye has proved highly ef­fec­tive at weed sup­pres­sion.

Some cover crops will need to be sprayed with glyphosate to en­sure they do not com­pete with the cash crop. But Groff stresses that her­bi­cides should be used strate­gi­cally like this only where nec­es­sary; the cover crop, ei­ther liv­ing or dead, should al­ways be used as the pri­mary weed sup­pres­sant.

One po­ten­tial op­tion to min­imise her­bi­cide use is to plant a frost-sus­cep­ti­ble cover crop as soon as the sum­mer cash crop is har­vested and be­fore win­ter sets in. The cover crop should then grow suf­fi­ciently be­fore be­ing killed off nat­u­rally by frost.

Dur­ing this growth pe­riod, it will have shaded out weeds. Once the cover crop is dead, its residue on the soil sur­face will con­tinue to sup­press fur­ther weed growth.

The cover crop should be planted as soon as pos­si­ble af­ter the cash crop has been har­vested. In all like­li­hood, residues of fer­tiliser and soil mois­ture from the cash crop in the soil will en­hance cover crop ger­mi­na­tion and growth. Th­ese nu­tri­ents will be re­cy­cled into the soil again once the cover crop is dead.

The de­vel­op­ment of shorter sea­son/faster ma­tur­ing maize and soya bean ge­net­ics of­fers an op­por­tu­nity for con­ser­va­tion agri­cul­ture farm­ers to gen­er­ate an in­come while max­imis­ing the ben­e­fits of in­ter-sea­son cover crops.

Groff points out that short­ersea­son ge­net­ics may not be suit­able for all crop farm­ers but it is worth plant­ing 5% to 10% of to­tal cash crop pro­duc­tion to th­ese ge­net­ics as a yield trial.

Farm­ers who con­duct their own on-farm re­search should repli­cate the trial at least three times on a land, and for at least three con­sec­u­tive sea­sons, then har­vest the trial crops at op­ti­mal ma­tu­rity to pro­vide ac­cu­rate yield data. Har­vest­ing a cash crop two to three weeks ear­lier than nor­mal will, in turn, al­low the farmer to plant a cover crop two to three weeks ear­lier.

“By the time the next cash crop plant­ing sea­son comes around, the cover crop will be two to three weeks older than in pre­vi­ous sea­sons. This means its biomass, as well as its ben­e­fits for soil health, sub­se­quent cash crops and farm prof­itabil­ity, will all be sig­nif­i­cantly greater,” says Groff.

In his own on-farm tri­als of shorter-sea­son maize and soya bean ge­net­ics, he found that their yields com­pared favourably with and some­times even out­per­formed longer-sea­son ge­net­ics. He adds, how­ever, that due to dif­fer­ences in soil types and cli­mate, this might not be the case for all farm­ers.

Cover crops slow run- off and help to in­crease wa­ter in­fil­tra­tion

the value of legumes

Groff points out that legu­mi­nous cash crops and cover crops cap­ture and use re­main­ing soil mois­ture, as well as cap­ture ni­tro­gen from the air and fix it in the soil for use. They also scav­enge any ni­tro­gen re­main­ing in the soil from pre­vi­ous crops. This can be as much as 30kg/ ha, so the farmer does not need to ap­ply as much costly in­or­ganic ni­tro­gen fer­tiliser to sub­se­quent cash crops.

“Us­ing a pre­ci­sion no-till planter to plant cover crops di­rectly into cash-crop residues straight be­hind the com­bine har­vester also saves on seed costs. With my pre­ci­sion planter, and with cer­tain cover crop va­ri­eties, I can get good ger­mi­na­tion and equiv­a­lent biomass with as lit­tle as half the seed rate I would need if I were us­ing a non­preci­sion no-till planter. This is a big cost sav­ing,” Groff says.

He sug­gests that South African grain farm­ers in­ves­ti­gate the fi­nan­cial fea­si­bil­ity of har­vest­ing their grain at 18% to 20% mois­ture con­tent, then hav­ing the grain ma­chine-dried to op­ti­mal stor­age and milling mois­ture con­tent in­stead of let­ting the grain dry on stand­ing crops.

Har­vest­ing grain crops two to three weeks ear­lier and ma­chine-dry­ing the grain will al­low th­ese farm­ers to plant their cover crops two to three weeks ear­lier, help­ing the cover crops to max­imise their growth and biomass, and hence soil health ben­e­fits.

An­other method of us­ing cover crops is biostrip-till­ing, where two va­ri­eties of cover crops, such as a legume and a high-biomass va­ri­ety, are planted in al­ter­nat­ing but closely spaced (say, 28cm) rows in the same land at the same time. Each will pro­vide dif­fer­ent ben­e­fits for soil health and sub­se­quent cash crops. A sub­se­quent cash crop could then be planted di­rectly into the row where the legume is grow­ing to ben­e­fit from the ni­tro­gen that the legume fixed into the soil. The residues of the high biomass cover crop va­ri­ety will shade out weeds in the cash crop in­ter-row while also pro­vid­ing ben­e­fi­cial or­ganic mat­ter to the soil.

With care­ful man­age­ment, biostrip-till­ing also en­ables a cover crop to be planted in the in­ter-rows of a cash crop. This helps shade out weeds and im­prove soil health.

less fer­tiliser needed

Be­tween his wheat and maize cash crops, Groff grows a di­verse multi-species cover crop that con­tains a sig­nif­i­cant pro­por­tion of ni­tro­gen-fix­ing legumes. This par­tic­u­lar cover crop pri­mar­ily com­prises radish, hairy vetch, sun­flower, common vetch, sweet blue lupin, sunn hemp, fenu­greek, Aus­trian win­ter pea, cal­en­dula, oats, phacelia, and fava bean.

“Once this multi-species cover crop is killed off by our cold win­ters, the earth­worms in the field go crazy on the residues,” he ex­plains. “In fact, the first time I tried this, the earth­worms ate so much that there was very lit­tle residue left. Now

I plant more sorghum in the mix to keep the soil sur­face cov­ered un­til plant­ing of the fol­low­ing cash crop.” Al­most the en­tire soil sur­face can be­come cov­ered with earth­worm cast­ings, which are an or­ganic fer­tiliser rich in ni­tro­gen.

“My sub­se­quent maize crops achieve prof­itable yields without my hav­ing to add in­or­ganic ni­tro­gen fer­tiliser.”

a cus­tomised mix

Groff cau­tions, how­ever, that this par­tic­u­lar multi-species cover crop is used on lands that are al­ready healthy af­ter many years of con­ser­va­tion agri­cul­ture prac­tices. He does not ad­vise novice con­ser­va­tion agri­cul­ture farm­ers to use his cover crop mix, and urges more ex­pe­ri­enced cover crop farm­ers to de­velop a pre-maize multi-species cover crop mix that works for their par­tic­u­lar pro­duc­tion en­vi­ron­ment.

• The next and fi­nal ar­ti­cle in this se­ries will focus on in­tro­duc­ing graz­ing live­stock to a con­ser­va­tion agri­cul­ture sys­tem, and the ben­e­fits this of­fers to soil health. • Email Steve Groff at [email protected]­er­crop­coach­, or visit cov­er­crop­coach­ • This pre­sen­ta­tion was given at the 2018 No-Till Con­fer­ence held from 4 to 6 Septem­ber in KwaZu­luNatal. Visit notill­

Steve Groff

ABOVE: Legu­mi­nous crops, such as th­ese beans, can re­duce the re­quire­ment for in­or­ganic ni­tro­gen fer­tiliser.

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