Competencies

04.01.2016
Hermann Limbers

Why is frost so important for black peat?

Our raw mate­ri­als

Black peat is an important raw mate­ri­al for the pro­duc­tion of gro­wing media. It con­fers ide­al pro­per­ties for the cul­ti­va­ti­on of young vege­ta­ble plants, and also forms an inte­gral part of substrates used for gro­wing bed­ding and pot plants. Black peat is also an important com­po­nent of con­tai­ner substrates for lon­ger-rota­ti­on crops, and is indis­pensable for com­mer­ci­al hor­ti­cul­tu­re.

Win­ter is the cru­ci­al sea­son when it comes to opti­mi­sing the qua­li­ty of black peat. Pro­lon­ged peri­ods of frost are ide­al­ly con­du­ci­ve to gene­ra­ting the desi­red pro­per­ties for this raw mate­ri­al. It needs to be fro­zen right through to ensu­re the necessa­ry phy­si­cal para­me­ters and to activa­te growth-pro­mo­ting humic acids. Why is this? And what hap­pens to the black peat when it free­zes?

As soon as the black peat has been extrac­ted using an exca­va­tor, the tur­ves, satu­ra­ted with water, are laid out on the bog sur­face. In frost con­di­ti­ons, when the black peat free­zes tho­rough­ly, its struc­tu­re and pro­per­ties alter: the water in the peat beco­mes ice, a pro­cess asso­cia­ted with phy­si­cal expan­si­on. When fro­zen, the black peat’s volu­me expands by around 9%, resul­ting in two advan­ta­ges: the air capa­ci­ty impro­ves from 5 to 10% by volu­me, and the water sto­rage capa­ci­ty increa­ses to > 400 g/100 g of dry mat­ter (> 65% by volu­me). High water and air capa­ci­ty are key cri­te­ria for high-qua­li­ty gro­wing media, as they have a high­ly posi­ti­ve impact on plant growth. The struc­tu­ral chan­ge cau­sed by free­zing is per­ma­nent, with the frost pre­ven­ting irrever­si­ble shrinkage of the black peat.

Frost also cau­ses the humic acids in black peat to decom­po­se. They have a high cati­on exchan­ge capa­ci­ty, bin­ding nut­ri­ents and spe­ci­fi­cal­ly making them avail­ab­le to plants during their growth pha­se. Humic acids also sti­mu­la­te root growth. The­se cha­rac­te­ris­tics make black peat an extre­me­ly important sub­stra­te ingre­dient, with frost play­ing the cru­ci­al role.

Howe­ver, in view of the increa­singly mild wea­ther con­di­ti­ons during the cold sea­son, the ques­ti­on ari­ses: can it be ensu­red that black peat will inde­ed con­ti­nue to free­ze over the long term? Bert von Seg­gern, Head of the Land Use Divi­si­on, is con­fi­dent that Klasmann-Deilmann is well pre­pa­red: “We always make pro­vi­si­on to have several years’ worth of black peat sup­plies in sto­rage, so that we can cope well with occa­sio­nal frost-free win­ters.” The com­pa­ny is also rea­dy to face more fre­quent mild win­ters: “We are now able to pro­vi­de an excel­lent black peat, which has com­pa­ra­ble pro­per­ties, even wit­hout suf­fi­ci­ent frost peri­ods. Admit­ted­ly, though, the extrac­tion pro­cess is more input-inten­si­ve and the raw mate­ri­al more expen­si­ve. So it’s good to know that addi­tio­nal resour­ces are avail­ab­le to us from the Bal­tic regi­on, whe­re frost is gua­ran­te­ed.”