Tillage: Erad­i­cate weeds and vol­un­teer cere­als through stub­ble cultivation

Loose, clump-free, crumbly and recon­sol­i­dat­ed – these are the opti­mum char­ac­ter­is­tics of cul­ti­vat­ed soils. Tillage is becom­ing increas­ing­ly impor­tant in achiev­ing this, par­tic­u­lar­ly in view of fer­tilis­er reg­u­la­tions and the restrict­ed use of plant pro­tec­tion prod­ucts. The main options for till­ing are stub­ble cul­ti­va­tion, pri­ma­ry tillage and seedbed prepa­ra­tion. In gen­er­al, as with all field work but espe­cial­ly tillage, it is impor­tant to avoid dam­age from soil com­paction. In this con­text, stub­ble cul­ti­va­tion becomes high­ly significant.

Goals of stub­ble cultivation

The pri­ma­ry goal of stub­ble cul­ti­va­tion is to reduce the amount of resid­ual seeds in the soil, and to encour­age weed seeds and vol­un­teer cere­als to ger­mi­nate by incor­po­rat­ing them just below the sur­face. This involves incor­po­rat­ing the organ­ic mat­ter into the soil at a shal­low depth and dis­rupt­ing cap­il­lary action in the soil, which pre­vents ris­ing water from evap­o­rat­ing. It usu­al­ly requires at least two pass­es. The first pass is shal­low and the sec­ond is at a medi­um depth, which enables the crop residues to be dis­trib­uted with­in the soil. To opti­mise the mix­ing effect and to break up tyre tracks, it is rec­om­mend­ed to work at a 15-degree angle to the direc­tion of the stub­ble dur­ing cul­ti­va­tion (around two thresh­ing widths). The tim­ing of stub­ble cul­ti­va­tion is high­ly weath­er-depen­dent. There should ide­al­ly be no rain­fall between the first, very shal­low cul­ti­va­tion pass and the fol­low­ing, deep­er cul­ti­va­tion pass. If the cul­ti­va­tor is set too deep dur­ing the first pass, the incor­po­rat­ed soil hori­zon can dry out, caus­ing the oppo­site effect. On the oth­er hand, to retain as much ground water as pos­si­ble, the ground should be tilled prompt­ly after harvesting.

Any resid­ual seeds from weeds or the pre­vi­ous crop can be erad­i­cat­ed either mechan­i­cal­ly or chem­i­cal­ly before sow­ing the next crop. This requires them to ger­mi­nate even­ly. Shal­low cul­ti­va­tion has addi­tion­al pos­i­tive effects, such pro­mot­ing a crumbly, well-con­sol­i­dat­ed soil tex­ture. When con­trol­ling weeds and unwant­ed plants mechan­i­cal­ly, the weath­er should be dry – includ­ing on the sub­se­quent days – to pre­vent the plants that are pulled out from con­tin­u­ing to grow. Con­trol­ling some par­tic­u­lar weeds, how­ev­er, requires mul­ti­ple pass­es of deep cul­ti­va­tion to bring their sub­ter­ranean rhi­zomes up to the sur­face. Tillage encour­ages the organ­ic mat­ter in the soil to rot. By mix­ing soil into the crop residues, it facil­i­tates their con­ver­sion, which pre­vents pathogens from being trans­ferred to the new crop.

Stub­ble cul­ti­va­tion process

Dur­ing the first pass of stub­ble cul­ti­va­tion, the soil under­neath the stub­ble should be bro­ken at the shal­low­est depth pos­si­ble (max. 5 cm) to avoid fall­en seeds from vol­un­teer cere­als and weeds from pen­e­trat­ing the deep­er soil lay­ers where they can­not ful­ly ger­mi­nate. Fur­ther­more, cul­ti­vat­ing the deep­er soil lay­ers con­sumes more ener­gy because a larg­er vol­ume of earth needs to be shift­ed. To suf­fi­cient­ly cap­ture root-prop­a­gat­ed and ger­mi­nat­ed weeds, the soil should be cul­ti­vat­ed at max­i­mum width. Wing share cul­ti­va­tors or disc har­rows are well suit­ed to this. Sev­en to ten days after the first pass of stub­ble cul­ti­va­tion, a sec­ond should fol­low depend­ing on the weath­er. Dur­ing the sec­ond pass, a work­ing depth of 10–12 cm should be main­tained. On com­pressed areas of soil, the work­ing depth should be adjust­ed as necessary.

The tools avail­able for shal­low stub­ble cul­ti­va­tion are duck­foot shares and discs (ser­rat­ed or smooth). Nar­row line spac­ing is advan­ta­geous. Wing shares, on the oth­er hand, are pri­mar­i­ly used for deep­er cul­ti­va­tion. An impor­tant cri­te­ri­on for suc­cess­ful stub­ble cul­ti­va­tion is the har­vest­ing qual­i­ty of the pre­vi­ous crop. If the straw is poor­ly dis­trib­uted or the stub­ble is too long, this can have a neg­a­tive effect on stub­ble cul­ti­va­tion. On the oth­er hand, to accel­er­ate micro­bial degra­da­tion, the straw needs to be chopped at a short­er length and with a high­er degree of splic­ing. This requires the use of a well-main­tained set of knives on the harvester.

How the seedbed is then pre­pared for seed sow­ing all depends on the sub­se­quent crop that is to be grown. If the seeds are small and require min­i­mal ener­gy for ger­mi­na­tion, such as sug­ar beet or oilseed rape, it is best to pre­pare a shal­low seedbed with a fine tex­ture. Where­as for cere­als with larg­er seeds that require more ener­gy to ger­mi­nate, a deep­er seedbed should be prepared.