Plant nutri­ents, the gold of the soil

Nutri­ent man­age­ment is of cen­tral impor­tance when it comes to crop pro­duc­tion. For metab­o­lism and bio­mass pro­duc­tion, plants require min­er­als and plant nutri­ents in addi­tion to light and water. These are absorbed when they are released in the ground­wa­ter as ions. If they are present in a bal­anced quan­ti­ty and in the right ratio to one anoth­er, plants can grow opti­mal­ly. The under-sup­ply of just one nutri­ent leads to loss­es in yield and quality.

As ear­ly as 1828, the agri­cul­tur­al sci­en­tist Carl Spren­gel iden­ti­fied twelve impor­tant nutri­ents for the first time. Jus­tus von Liebig also showed that plants absorb nutri­ents from the soil. In 1855, he devel­oped his “law of the min­i­mum”, in which growth and yield were deter­mined by the nutri­ent present in the least amount, mea­sured against the plant’s requirements.

As we know today, plants require 14 min­er­als, which can­not be replaced by oth­er sub­stances. This is dif­fer­en­ti­at­ed accord­ing to main nutri­ents and trace nutrients.

Plant nutri­ents and the impact on soil fertility

Trace nutri­ents – chlo­rine, iron, man­ganese, boron, zinc, cop­per, molyb­de­num and nick­el sup­port meta­bol­ic process­es and pho­to­syn­the­sis. In addi­tion, they improve resis­tance and ger­mi­na­tion capac­i­ty. In com­par­i­son to main nutri­ents, trace nutri­ents are required by plants in low­er quan­ti­ties (about 5–500 g/ha). Main nutri­ents – nitro­gen, potas­si­um, cal­ci­um, mag­ne­sium, phos­pho­rus and sul­phur – are there­fore required in larg­er quan­ti­ties (20–250 kg/ha).

The indi­vid­ual main nutri­ents have dif­fer­ent func­tions and modes of action:

• Nitro­gen ensures the growth of shoots and leaves and is a build­ing block for pro­tein and chloro­phyll. A defi­cien­cy leads to growth retar­da­tion, light leaves and death. An excess caus­es mass growth at the expense of the crop. The plants are also more sus­cep­ti­ble to disease.
• Potas­si­um reg­u­lates the water bal­ance, increas­es sta­bil­i­ty and fibre qual­i­ty and improves resis­tance to the cold. A defi­cien­cy dis­rupts the water bal­ance, so that the leaves wilt. In addi­tion, this caus­es an increased sus­cep­ti­bil­i­ty to dis­ease. The shelf life and taste of the veg­eta­bles is worse and the vit­a­min con­tent decreas­es. On the oth­er hand, plants can eas­i­ly process any excess.
• Cal­ci­um also reg­u­lates the water bal­ance, sta­bilis­es the plant tis­sue and improves the qual­i­ty of the crop. Any defi­cien­cy caus­es chloro­sis in young shoots and imped­ed growth. An excess does not cause any sig­nif­i­cant damage.
• Mag­ne­sium is essen­tial for the for­ma­tion of the green coloura­tion of the leaf (chloro­phyll). It is required for the cre­ation of car­bo­hy­drates, fats and pro­teins. A defi­cien­cy leads to meta­bol­ic dis­or­ders with bleach­ing of the leaves and growth inhi­bi­tion. Excess is rel­a­tive­ly rare.
• Phos­pho­rus pro­motes flower and fruit for­ma­tion, encour­ages root growth, improves win­ter har­di­ness and is indis­pens­able for ener­gy metab­o­lism. A phos­phate defi­cien­cy can be iden­ti­fied from growth inhi­bi­tion. Any defi­cien­cy over a longer peri­od of time leads to a red­dish coloura­tion of the leaves, which final­ly die. An excess gen­er­al­ly has no neg­a­tive consequences.
• Sul­phur is required for the cre­ation of pro­teins and vit­a­mins. It also pro­motes the effect of nitro­gen. Sul­phur defi­cien­cy hin­ders growth due to a reduced for­ma­tion of chloro­plas­ts and chloro­phyll, which leads to yel­low­ing. An excess of sul­phur does not cause any direct dam­age, but can result in the acid­i­fi­ca­tion of the soil.

Sources of plant nutri­ents and losses

Every growth cycle removes nutri­ents from the soil. The nutri­ents must be replaced by fer­tilis­ers so that the soil does not become impov­er­ished and thus inhib­it plant growth. The type, quan­ti­ty and tim­ing are based on plant require­ments and nutri­ent con­tent of the soil.

The most impor­tant min­er­al fer­tilis­ers are nitro­gen, phos­phate, potas­si­um and cal­ci­um. They con­tain the same nutri­ents that are found in nature. Accord­ing to stud­ies, the soil remains fer­tile even with min­er­al fer­til­i­sa­tion alone. Min­er­al fer­tilis­ers con­tain nutri­ent quan­ti­ties that are avail­able regard­less of the sea­son. They allow low-loss fer­til­i­sa­tion and can be spread even­ly. In addi­tion, min­er­al fer­tilis­ers can reduce the cost of the pro­duc­tion of food, as the yield per field increas­es. On the oth­er hand, min­er­al fer­tilis­ers favour con­cen­tra­tion on a few types of crops, and nitro­gen-col­lect­ing legumes are less favoured. If only min­er­al fer­tilis­ers are used, mea­sures for main­tain­ing the humus con­tent are required. Inten­sive min­er­al fer­til­i­sa­tion also pro­motes the growth of high-qual­i­ty feed grass in pas­ture­land. Less com­pet­i­tive species are left behind and diver­si­ty decreases.

In the case of farm­yard manure, a nutri­ent cycle is cre­at­ed, which is both eco­log­i­cal­ly and eco­nom­i­cal­ly sen­si­ble. There­fore, the recy­cling of the organ­ic nutri­ents in your oper­a­tion has always had pri­or­i­ty. The organ­ic sub­stance also con­tributes to sta­bil­is­ing the humus con­tent of the soil. How­ev­er, the nutri­ent con­tent fluc­tu­ates con­sid­er­ably, and exact fer­tilis­er plan­ning is dif­fi­cult to use, espe­cial­ly since the nutri­ents are not always avail­able in a time­ly and a quan­ti­ty-ori­ent­ed man­ner. The imple­men­ta­tion in the soil is like­wise dif­fi­cult to cal­cu­late; the nutri­ent effect can­not be reli­ably pre­dict­ed. The envi­ron­ment is con­t­a­m­i­nat­ed by releas­ing the nutri­ents and through the escape of ammo­nia. Since farm­yard manure can only be sen­si­bly used at cer­tain times of the year, it must be stored in a low-loss man­ner. How­ev­er, stor­age space is often lim­it­ed. There­fore, there is a risk that it is used at times that are not opti­mal for plant nutri­tion. In addi­tion, over-use of fer­tilis­er often occurs, since farm­yard manure is gen­er­al­ly eas­i­er to apply to near­by fields.

Despite need-based fer­tilis­er appli­ca­tion, nutri­ent loss can­not be com­plete­ly avoid­ed. Here, in par­tic­u­lar, phos­phate and water eutroph­i­ca­tion, nitro­gen washout in the ground­wa­ter and in sur­face water, ammo­nia volatil­i­sa­tion and nitro­gen loss in the form of nitrous oxide must be tak­en into account.

Use of fer­tilis­er accord­ing to good spe­cial­ist prac­tice can min­imise nutri­ent loss­es and achieve high yields for the long term. In addi­tion, the har­vest qual­i­ty can be improved through this, plant pro­tec­tion and resis­tance can be favourably influ­enced and the soil fer­til­i­ty can be preserved.