Between rape blos­som sea­son and ripen­ing – this is the cor­rect har­vest­ing peri­od for rapeseed

In the EU agri­cul­tur­al land for rape­seed in the EU has decreased to a marked degree in the last few years. Among oth­er fac­tors, the adverse weath­er con­di­tions and increas­ing pest pres­sure have result­ed in a sig­nif­i­cant reduc­tion in agri­cul­tur­al land. The record for the small­est area sown until now was achieved in Ger­many in 2018; in that year only 850,000 ha were sown. In France only 950,000 ha have been sown for this year’s har­vest. In 2020 1.1 mil­lion ha were sown. Con­verse­ly, in Poland the agri­cul­tur­al land for rape­seed cul­ti­va­tion has remained rel­a­tive­ly sta­ble in the last three years, at just under 900,000 ha. The low­est lev­el was reached in the EU for the 2019 har­vest, when the area was a scant 5 mil­lion t. The area of rape­seed for the 2021 har­vest is 5.2 mil­lion ha (exclud­ing the Unit­ed King­dom, cur­rent­ly with 330,000 ha).

Dif­fer­ing cli­mat­ic con­di­tions for the growth of rape­seed pre­vail in Europe; in addi­tion to the region­al weath­er con­di­tions, cli­mate affects the blos­som sea­son. The weath­er in France is influ­enced pre­dom­i­nant­ly by a mar­itime cli­mate. In Ger­many the mar­itime cli­mate is marked by con­ti­nen­tal influ­ences. In Poland the pre­vail­ing cli­mate is pre­dom­i­nant­ly con­ti­nen­tal. The har­vest sea­son also moves accord­ing­ly, i.e. as a rule France is the first to begin thresh­ing. In order to assess the devel­op­ment of the crops, it is pos­si­ble to, among oth­er things, analyse satel­lite images and in this way deter­mine the cor­rect period.

This year the field crops in Europe have come through the win­ter with var­ied suc­cess. In April France was hit by severe frosts; loss of rev­enue is to be expect­ed. Cur­rent esti­mates start from a crop yield of 2.9 mil­lion t (pre­vi­ous year 3.3 mil­lion t). As in the pre­vi­ous year, a yield of approx­i­mate­ly 3.5 mil­lion t is antic­i­pat­ed for Ger­many. Here, the crops are pre­dom­i­nant­ly in good con­di­tion. How­ev­er, by virtue of the cool months of April and May the over­all devel­op­ment of the plants is lag­ging behind by about two to three weeks. The fore­casts also antic­i­pate a har­vest like that of the pre­vi­ous year for Poland, at approx­i­mate­ly 2.7 mil­lion tons. In order to under­take an accu­rate analy­sis of the influ­ence of the weath­er, his­toric weath­er data from the respec­tive loca­tions are an advantage.

Achiev­ing steady ripen­ing for the rape­seed harvest

As well as the cor­rect har­vest peri­od, the influ­ence of the weath­er dur­ing the rosette stage is cru­cial for the yield, since the main shoots with numer­ous side shoots devel­op from the rosettes. The num­ber of pods is also an impor­tant cri­te­ri­on for the yield. As is gen­er­al­ly known, these ripen from above to below and thus are not all ready for har­vest­ing at the same time. In addi­tion, the har­vest­ing peri­od depends on the vari­ety select­ed. The pre­req­ui­sites for the cor­rect har­vest peri­od are the pro­por­tion of brown pods and black seeds, as well as a mois­ture con­tent of max. 11%. Rape­seed is fre­quent­ly har­vest­ed too ear­ly, in order to avoid work­load peaks in oth­er crops or because there is a fear of a high fail­ure rate. The cru­cial ele­ment for the yield here is how ripe the pods are in the mid­dle and low­er area of the plants. They make the great­est con­tri­bu­tion to a high yield. If the upper pods are burst­ing open, this is still not an indi­ca­tion that the pods in the low­er areas are also ready for har­vest­ing. As a rule, these pre-har­vest loss­es must be tak­en into account. More­over, ripen­ing at a stead­ier rate can be assist­ed by using growth reg­u­la­tors. They pro­mote the devel­op­ment of the lat­er­al shoots and lim­it growth in height. If ripen­ing is incon­sis­tent and there is heavy weed infes­ta­tion a chem­i­cal prod­uct for quick­er, more even ripen­ing can be used. In this case var­i­ous leaf her­bi­cides can be used. If thresh­ing is under­tak­en too ear­ly, this has a neg­a­tive result not only on the oil con­tent, but on the har­vest as a whole. In addi­tion, the unripe grains clog the com­bine har­vester engine, which impedes the har­vest­ing. There are var­i­ous Farm Man­age­ment Infor­ma­tion Sys­tems (FMIS), which allow you to view clear­ly and analyse the rel­e­vant data for the plan­ning, mon­i­tor­ing and analysing of the pro­ce­dures on the fields and pro­vide doc­u­men­ta­tion on the com­plete harvest.

Pre­vent­ing vol­un­teer rape

If the rape­seed seeds fall from the pods before or dur­ing har­vest­ing and ger­mi­nate again in the sub­se­quent crop, we talk about vol­un­teer rape. High pro­por­tions of vol­un­teer rape jeop­ar­dise the cul­ti­va­tion sta­bil­i­ty, cause high­er costs and can great­ly reduce the yield. The rule of thumb is that, if the pro­por­tion of vol­un­teer rape is approx­i­mate­ly 10%, the yield poten­tial of the main crop is impaired by at least 5%.

Soil cul­ti­va­tion, which should be under­tak­en imme­di­ate­ly after har­vest­ing, is cru­cial for the reduc­tion of vol­un­teer rape. The more time, which elaps­es between the har­vest peri­od and sub­se­quent cul­ti­va­tion, the more chances there are to con­trol vol­un­teer rape. The aim of soil cul­ti­va­tion is to stim­u­late the rape seeds to ger­mi­nate. It has been shown that shal­low tillage to a max­i­mum depth of 3–4 cm is the most suit­able sys­tem. If there is suf­fi­cient mois­ture in the soil the great­est part of the vol­un­teer rape sprouts of its own accord. Con­verse­ly, if the soil is tilled to a greater depth, the seeds are buried and become dor­mant. Then the seeds are able to sprout con­tin­u­ous­ly in the fol­low­ing year. Anoth­er method for reduc­ing the pro­por­tion of vol­un­teer rape involves a high­er sow­ing den­si­ty. With this method, the high­er sow­ing den­si­ty improves the sup­pres­sion of the com­pet­i­tive­ly more inhib­it­ed vol­un­teer rape.