Fer­til­i­sa­tion accord­ing to plan 

The end of one har­vest is the begin­ning of anoth­er. After all, the next crop is already in the ground by autumn. The main chal­lenge that they face is rein­tro­duc­ing the extract­ed nutri­ents into the soil to ensure opti­mal grow­ing con­di­tions. In our arti­cle “Accu­rate­ly adjust­ing soil nutri­ents”, we dis­cussed soil para­me­ters and the con­se­quences they have on fer­til­i­sa­tion in detail.
Before tar­get­ed fer­til­i­sa­tion can be car­ried out, a thor­ough inves­ti­ga­tion into the nutri­ent require­ments must be under­tak­en as a pri­or­i­ty. There are sev­er­al par­tial­ly com­ple­men­tary ways of achiev­ing this. Field and pot exper­i­ments, chem­i­cal crop analy­ses and defi­cien­cy symp­tom diag­noses pro­vide ini­tial indi­ca­tions of the type and extent of fer­til­i­sa­tion required. These meth­ods look at the prop­er­ties of the crops, their chem­i­cal com­po­si­tion and the fac­tors influ­enc­ing their health. Defi­cien­cy symp­toms indi­cate an insuf­fi­cient sup­ply of nutri­ents to the crops.

Soil test­ing pro­vides even more pre­cise infor­ma­tion about the state of sup­ply in arable fields. For chem­i­cal analy­sis, sam­ples are usu­al­ly tak­en from the top­soil up to a depth of 60 cen­time­tres, after the pre­ced­ing main crop has been har­vest­ed in autumn or spring. How­ev­er, there should also be a gap of at least six weeks between sam­pling and the last pass of tillage or fer­til­i­sa­tion. On larg­er areas with het­ero­ge­neous sec­tions, the fields must be split into yield zones. The pre­ci­sion farm­ing sec­tor has pro­duced a range of dig­i­tal tools to help iden­ti­fy these sec­tions. The Crop View com­po­nent from 365FarmNet also enables the yield poten­tial of crops to be deter­mined. The com­po­nent uses his­toric satel­lite data to analyse crops from mul­ti­ple years. The results can then be used to cre­ate a sam­pling plan. Mul­ti­ple indi­vid­ual sam­ples are tak­en from the field sec­tions and com­bined to make mixed sam­ples for lab­o­ra­to­ry analy­sis. Extrac­tion process­es in com­bi­na­tion with dif­fer­ent sol­vents then deter­mine the avail­able nutri­ents and the pH val­ue of the soil. If the soil con­tains a high pro­por­tion of organ­ic mat­ter, the nutri­ent con­tents are giv­en per vol­ume unit of soil. As such, the vol­u­met­ric weight (or bulk den­si­ty) of the soil must also be cal­cu­lat­ed. All this infor­ma­tion can help to improve the cor­re­la­tion between the soil tests and the actu­al nutri­ent sup­ply as the root pen­e­tra­tion can be tak­en into account.

Fer­til­i­sa­tion balancing

Prop­er fer­til­i­sa­tion accord­ing to good pro­fes­sion­al prac­tice should pro­vide crops with all the nutri­ents they need. At the same time, exces­sive fer­tilis­er dos­es and the asso­ci­at­ed soil, water and air pol­lu­tion caused by nutri­ent loss­es should be avoid­ed. To deter­mine the fer­til­i­sa­tion require­ment, the fer­tilis­er com­po­si­tion, nutri­ent extrac­tion by the plants, tar­get­ed yields, soil reserves, replen­ish­ment poten­tial and nutri­ent inputs must all be tak­en into account. Indus­tri­al­ly man­u­fac­tured fer­tilis­ers come with pre­cise infor­ma­tion about their com­po­si­tion. This enables the quan­ti­ty of dis­trib­uted ele­ments to be pre­cise­ly deter­mined. For organ­ic fer­tilis­ers pro­duced on a farm, the nutri­ent con­cen­tra­tions are exam­ined in a lab­o­ra­to­ry. The nutri­ent reserves and poten­tial of the soil and the lev­el of nutri­ent extrac­tion by the crops are also analysed in a lab­o­ra­to­ry using the meth­ods men­tioned. Nutri­ent inputs are most­ly pro­vid­ed by means of organ­ic and inor­gan­ic fer­til­i­sa­tion, which is car­ried out with­in the strict lim­i­ta­tions of applic­a­ble fer­tilis­er reg­u­la­tions, such as the Ger­man Fer­tilis­er Appli­ca­tion Ordinance.

A range of soft­ware solu­tions are avail­able to help with fer­til­i­sa­tion man­age­ment. They deter­mine the dead­lines, bound­aries and excep­tions for spe­cif­ic farms, bring­ing struc­ture and sim­plic­i­ty to fer­til­i­sa­tion mea­sures. One exam­ple is the DELOS Nutri­ent Man­age­ment com­po­nent from 365FarmNet. It con­tains all the lat­est reg­u­la­tions from the indi­vid­ual fed­er­al states in Ger­many to enable fer­tilis­er require­ments to be cal­cu­lat­ed reli­ably and pre­cise­ly.
Inputs that enter the soil through wet and dry depo­si­tion are also impor­tant for main­tain­ing the nutri­ent bal­ance dur­ing fer­til­i­sa­tion.. In the case of wet depo­si­tion, sub­stances that are dis­solved in rain or mist accu­mu­late in the soil. This type of input can be deter­mined by col­lect­ing pre­cip­i­ta­tion in spe­cial bulk col­lec­tion tanks. Experts refer to dry depo­si­tion when sol­id or gaseous par­ti­cles that are present in the air and deposit­ed in the soil. The larg­er the field sur­face the sub­stance has to set­tle on, the high­er the lev­el of depo­si­tion. There­fore, the val­ues detect­ed on veg­e­tat­ed areas are high­er than those on unveg­e­tat­ed arable land. Both effects dif­fer in their localised man­i­fes­ta­tion. In this con­text, high nitro­gen inputs com­mon­ly occur in areas with large cat­tle pop­u­la­tions and their asso­ci­at­ed NH³ emis­sions. Like­wise, high­er lev­els of sul­phur are often found in crops grow­ing near indus­tri­al or urban areas. In areas neigh­bour­ing bod­ies of salt­wa­ter, high­er con­cen­tra­tions of sodi­um and mag­ne­sium are often detect­ed in the soil. These cor­re­la­tions must be con­sid­ered dur­ing the fer­til­i­sa­tion in order to avoid any over­sup­ply of the areas.

Sig­nif­i­cant nutri­ent out­puts main­ly occur as a result of nutri­ent extrac­tion by crops and field clear­ing after har­vest. The lev­el of nutri­ents extract­ed by crops depends on the crop type, vari­ety and yield. Any crop residues remain­ing in the field are classed as nutri­ent inputs and must be suit­ably account­ed for dur­ing fer­til­i­sa­tion. Fur­ther nutri­ent loss­es result from sur­face runoff, par­tic­u­lar­ly on high­ly com­pact­ed field sec­tions. How­ev­er, nutri­ents are not only lost via the sur­face, but also as a result of runoff in inter­me­di­ate and ground­wa­ter, or via drains. These nutri­ent out­puts depend on the type and struc­ture of the soil. Gaseous loss­es, par­tic­u­lar­ly of nitro­gen com­pounds, must also be tak­en into account for fertilisation.

Impor­tant nutri­ents for fertilisation 

For effec­tive fer­til­i­sa­tion, all the required nutri­ents must be har­monised. The lim­it­ing fac­tor here is the ele­ment that is least present in the soil solu­tion (Liebig’s law of the min­i­mum). The main nutri­ent ele­ments include – in decreas­ing order of occur­rence in plant mat­ter – nitro­gen, potas­si­um, cal­ci­um, mag­ne­sium, phos­pho­rus and sul­phur. In addi­tion, sil­i­con and sodi­um are also impor­tant for cer­tain crop species. 

In terms of quan­ti­ty, nitro­gen is the most com­mon­ly occur­ring. As such, it is one of the core ele­ments of crop nutri­tion and an impor­tant build­ing block for microor­gan­isms. It is also a com­po­nent of many organ­ic com­pounds, such as amino acids, vit­a­mins and chloro­phyll. As is only rarely found in par­ent rock and min­er­al soil mat­ter, nitro­gen has to be added to arable land via suit­able fer­tilis­ers. The nitro­gen sup­ply of crops is fre­quent­ly a yield-lim­it­ing fac­tor. As such, an ade­quate dose usu­al­ly results in a high yield. 

Potas­si­um is respon­si­ble for the osmot­ic pres­sure in crops and there­fore for reg­u­lat­ing the water bal­ance. Sim­i­lar to mag­ne­sium, it is also nec­es­sary for the acti­va­tion of cer­tain enzymes. A good sup­ply of potas­si­um increas­es drought and frost resis­tance. A defi­cien­cy, on the oth­er hand, can cause increased leaf wilt, par­tic­u­lar­ly around the edges of the leaves. This in turn can cause chloro­sis and necro­sis in crops.

Phos­pho­rus is present in the Earth’s crust and is an impor­tant ele­ment for all liv­ing things. As part of the food chain, it makes its way via the soil to plants, ani­mals and ulti­mate­ly humans. Phos­pho­rus is respon­si­ble for sup­ply­ing cells with ener­gy (ADP, ATP syn­the­sis), and is used as a cell build­ing block and in the for­ma­tion of organ­ic sub­stances. A lack of phos­pho­rus in soil has a neg­a­tive effect on crop growth, par­tic­u­lar­ly in the form of defi­cien­cy symp­toms such as necro­sis and chlorosis.

Sul­phur is a com­po­nent of many plant con­stituents, such as amino acids, enzymes and vit­a­mins. A lack of sul­phur dis­rupts the syn­the­sis of pro­tein and chloro­phyll, which caus­es yel­low­ing, ini­tial­ly in young leaves then lat­er all leaves. In rape­seed, a sul­phur defi­cien­cy can result in a com­plete yield loss. A suf­fi­cient sul­phur sup­ply is there­fore incred­i­bly impor­tant for the pro­duc­tion of high-qual­i­ty food.

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