A cur­mud­geon takes on fi­nan­gling

Al­ter­na­tive ap­proaches to soil fer­til­ity have been chal­lenged.

NZ Grower - - Agronomist -

In Au­gust Dr Ants Roberts, the chief sci­en­tific of­fi­cer for Ravens­down Fer­tiliser Co-op­er­a­tive, gave three lec­tures, the first at Massey Uni­ver­sity, the se­cond at Ruakura Re­search Cen­tre and the fi­nal one at Lin­coln Uni­ver­sity, which is the cus­tom for the re­cip­i­ent of the Ray Brougham Tro­phy. It’s awarded each year by the New Zealand Grass­lands Trust to some­body who has made a sig­nif­i­cant con­tri­bu­tion to pas­toral agri­cul­ture in New Zealand.

Roberts talk was en­ti­tled Soil Fer­til­ity Fi­nan­gling: A Cur­mud­geons View and he ex­plained fi­nan­gling as the use of trick­ery or crafti­ness to achieve ones aim, and cur­mud­geon as a crusty, ill­tem­pered,

He be­gan with a quote from the Re­gen­er­a­tion In­ter­na­tional web­site where pro­po­nents of ‘re­gen­er­a­tive agri­cul­ture’ are crit­i­cal of con­ven­tional agri­cul­ture claim­ing it to be de­gen­er­a­tive agri­cul­ture. The quote stated, “The key to re­gen­er­a­tive agri­cul­ture is that it not only ‘does no harm’ to the land but ac­tu­ally im­proves it, us­ing tech­nolo­gies that re­gen­er­ate and re­vi­talise the soil and the en­vi­ron­ment. Re­gen­er­a­tive agri­cul­ture leads to healthy soil, ca­pa­ble of pro­duc­ing high qual­ity, nu­tri­ent dense food while si­mul­ta­ne­ously im­prov­ing, rather than de­grad­ing land, and ul­ti­mately lead­ing to pro­duc­tive farms and healthy com­mu­ni­ties and economies.’”

In the past cou­ple of decades there have been a num­ber of ar­ti­cles in the pop­u­lar press and farm­ing me­dia on sus­tain­able and re­gen­er­a­tive agri­cul­tural prac­tices by self­pro­claimed ex­perts who are crit­i­cal of con­ven­tional fer­tiliser prac­tices in re­la­tion to soil science which have worked well for many decades. In his talk Roberts dis­cussed a num­ber of these al­ter­na­tive ap­proaches to soil fer­til­ity, yet which have failed to show merit when put through sci­en­tific rigour. His crit­i­cisms in­cluded Fine Par­ti­cle Ap­pli­ca­tion (FPA) or liquifi­ca­tion of main­stream fer­tilis­ers such as urea and DAP, Base Sat­u­ra­tion Ca­tion Ra­tio (BCSR) the­ory, some­times re­ferred to as Al­brecht the­ory, the use of hu­mates to build soil or­ganic mat­ter lev­els, and di­cal­cium phos­phate com­pared with us­ing su­per­phos­phate and lime.

With FPA or ap­ply­ing fer­tilis­ers in liq­uid form he re­ferred to trial work which has shown that whether a prod­uct is sprayed on or ap­plied in dry gran­u­lar form, there’s no dif­fer­ence in over­all pro­duc­tion.It’s the quan­tity of nu­tri­ent ap­plied which de­ter­mines the re­sponse. Farm­ers and grow­ers how­ever who spray on sol­u­ble fer­tilis­ers and are also ap­ply­ing a plant growth hor­mone such as gib­berel­lic acid may see ex­tra pro­duc­tion ben­e­fits, and ob­vi­ously if one is in­clud­ing chem­i­cal sprays such as her­bi­cides, pes­ti­cides or fungi­cides, so long as these are com­pat­i­ble with the fer­tiliser ma­te­rial, then there may be merit in fer­til­is­ing and spray­ing these to­gether in a sin­gle pass.

FPA has his­tor­i­cally been pro­moted as need­ing less over­all fer­tiliser ma­te­rial to achieve the same amount of pro­duc­tion and Roberts’ talk showed this not to be the case.

The BCSR the­ory was first pro­moted by Amer­i­can soil sci­en­tists Drs Beare and Toth and later re­fined by Dr Wil­liam Al­brecht from Mis­souri State Uni­ver­sity in the 1940s and 1950s. The the­ory is that there is an ideal ra­tio of the pos­i­tive el­e­ments (cations) cal­cium, mag­ne­sium, potas­sium and sodium which are at­tached to the neg­a­tively charged soil par­ti­cles where cal­cium should make up 60-75 per­cent, mag­ne­sium 10-20 per­cent, potas­sium twoto five per­cent and sodium from 0.5 to five per­cent of the ex­change sites of the soil’s Ca­tion Ex­change Ca­pac­ity (CEC).

Later work by one of Al­brecht’s own stu­dents, McLean, and oth­ers showed there is no ideal ra­tio, but that these el­e­ments should be ap­plied to the soil based on whether they were de­fi­cient or not which is com­monly re­ferred to as the Suf­fi­ciency Level of Avail­able Nu­tri­ents (SLAN) the­ory. We use this in New Zealand where it’s bet­ter known as MAF Units for cal­cium, mag­ne­sium, potas­sium and sodium. Their re­search showed that suf­fi­ciency lev­els are a bet­ter pre­dic­tor of crop re­sponses than us­ing base sat­u­ra­tion ra­tios.

Af­ter Roberts’ talk in Hamil­ton I men­tioned to him some re­cent

re­search done by Dr Tim Rein­bott of Mis­souri State Uni­ver­sity which he pre­sented at the Amer­i­can So­ci­ety of Agronomy and Soil Science So­ci­ety of Amer­ica an­nual con­fer­ence last year. This re­search showed that us­ing the Al­brecht sys­tem gave im­proved yields in corn and soya bean crops and that there were some soil health im­prove­ments us­ing the Al­brecht ap­proach com­pared with a con­ven­tional fer­tiliser in­put ap­proach.

For me per­son­ally when ad­vis­ing farm­ers and grow­ers I con­sider both base sat­u­ra­tion ra­tios and suf­fi­ciency lev­els as I think there is some over­lap in terms of pro­duc­tion and qual­ity and in the case of live­stock, par­tic­u­larly dairy cows, that hav­ing cor­rect cal­cium:potas­sium and mag­ne­sium:potas­sium ra­tios can im­prove an­i­mal health. For hor­ti­cul­tural clients, hav­ing suf­fi­cient cal­cium and mag­ne­sium is vi­tal in terms of shelf life and keep­ing qual­ity in some fruit and veg­etable crops.

When it came to the topic of hu­mates which are prod­ucts ex­tracted from lig­nite and leonardite coal, Roberts showed that most of our soils al­ready have large quan­ti­ties of or­ganic mat­ter and soil car­bon. Adding a small amount of hu­mate prod­ucts (hu­mic acid, ful­vic acid and humin) would make very lit­tle dif­fer­ence. He stressed the im­por­tance of try­ing to main­tain good or­ganic mat­ter lev­els, and although this can be done with per­ma­nent pas­ture when it comes to con­tin­u­ous crop­ping, pul­veris­ing the soil to a pulp and thereby de­stroy­ing soil struc­ture and de­plet­ing the soil of valu­able or­ganic mat­ter (car­bon) lessens the soil qual­ity and pro­duc­tive ca­pac­ity.

Or­ganic mat­ter in the soil pro­vides so many ben­e­fits in­clud­ing im­proved mois­ture and nu­tri­ent re­ten­tion, re­duc­ing soil com­paction and sur­face crust­ing, im­prov­ing wa­ter in­fil­tra­tion, pro­vid­ing food and a valu­able home for im­por­tant soil mi­cro-or­gan­isms and earth­worms, prevent­ing soil ero­sion and nu­tri­ent run-off and im­prov­ing the macro and mi­cro poros­ity of the soil.

As for re­verted and di­cal­cium phos­phate fer­tilis­ers which are blends of su­per­phos­phate and lime ma­te­ri­als which are wet­ted and left to re­act and go hard, then crushed and re-screened, Roberts showed there was no greater value in us­ing these com­pared with ap­ply­ing lime and su­per­phos­phate sep­a­rately. Di­cal­cium phos­phate prod­ucts are less avail­able to plants on ap­pli­ca­tion com­pared with mono­cal­cium phos­phate (su­per­phos­phate) fer­tilis­ers, and that the only ex­cep­tions where di­cal­cium phos­phate prod­ucts could be more ben­e­fi­cial than su­per­phos­phate are the pak­ihi sand soils of the West Coast and the pod­sol soils of North­land where the Anion Stor­age Ca­pac­ity (ASC), some­times re­ferred to as phos­phate re­ten­tion per­cent­age is very low. Con­se­quently phos­pho­rus is prone to leach­ing out, so hav­ing less sol­u­ble forms of phos­phate might be ad­van­ta­geous.

Dr Ants Roberts’ talk can be viewed on-line at http://www.youtube.com/watch?v=4eCnFZ9Tros

Robin Boom / CPAg, Mem­ber of the In­sti­tute of Pro­fes­sional Soil Sci­en­tists

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