Look af­ter soil for sake of fu­ture gen­er­a­tions

Matamata Chronicle - - Rural Delivery - By BALA TIKKISETTY

Max­imis­ing eco­nomic ef­fi­ciency and pro­tect­ing the environment re­quires the sus­tain­able man­age­ment of our Waikato soils.

A good def­i­ni­tion of sus­tain­able re­source man­age­ment is meet­ing the needs of the present with­out com­pro­mis­ing the abil­ity to meet the needs of fu­ture gen­er­a­tions.

Soil man­age­ment is sus­tain­able when it lets us get what we need to­day with­out com­pro­mis­ing the ca­pac­ity of the soil to pro­vide for fu­ture needs.

Waikato Re­gional Coun­cil’s lat­est soil qual­ity sur­vey in­for­ma­tion has re­vealed sev­eral in­ter­est­ing is­sues in terms of the ex­tent and di­rec­tion of changes in soil con­di­tion.

The coun­cil mea­sured eight pri­mary prop­er­ties to as­sess soil qual­ity. Chem­i­cal and bi­o­log­i­cal char­ac­ter­is­tics were as­sessed by to­tal car­bon (C) con­tent, to­tal ni­tro­gen (N), po­ten­tially min­er­al­is­able N, phos­pho­rus (Olsen P), soil acid­ity (pH), ag­gre­gate sta­bil­ity and de­rived mea­sure­ments such as the C:N ra­tio.

Soil phys­i­cal con­di­tion was as­sessed us­ing dry bulk den­sity and macro­p­oros­ity (a mea­sure of pore spa­ces in soil).

These soil phys­i­cal mea­sure­ments pro­vided mea­sures of soil com­paction, the sta­bil­ity of soil ag­gre­gates, the amount of space be­tween soil ag­gre­gates (pores) and the den­sity of the soil.

In the past six years, in­clud­ing the lat­est 2010-11 re­sults, of 145 sites mon­i­tored by the coun­cil:

31 met all soil qual­ity tar­gets (21 per cent av­er­age over six years, down from an av­er­age of 26 per cent over the five years till 2009-10).

50 failed one tar­get (34 per cent av­er­age, the same as pre­vi­ous five years’ av­er­age)

64 sites failed two or more tar­gets (44 per cent av­er­age, up from the 40 per cent av­er­age of the pre­vi­ous five years).

Of the 30 sites sam­pled in 2010-11, 13 were on dairy soils, five on crop­ping and hor­ti­cul­ture soils, eight on dry­s­tock soils, three were on na­tive veg­e­ta­tion and one site was sup­port­ing plan­ta­tion forestry.

Com­paction on dairy and dry­s­tock sites in the Waikato re­mains a par­tic­u­lar con­cern.

Com­paction re­duces the num­ber and size of pores avail­able for water and gas move­ment in soil. It re­duces aer­a­tion, nu­tri­ent up­take, root growth and dis­tri­bu­tion, and po­ten­tially de­creases in­fil­tra­tion and in­creases runoff.

The most sen­si­tive in­di­ca­tor of com­paction is macro­p­oros­ity.

Pre­vi­ous re­search re­veals that macro­p­oros­ity be­low 10 per cent will in­hibit pas­ture growth.

While New Zealand’s pas­toral farm­ing sys­tems are very ef­fi­cient at gen­er­at­ing pro­duce, they can lead to nu­tri­ents, both ni­tro­gen and phos­pho­rus, de­grad­ing sur­face and ground­wa­ter qual­ity.

In the Waikato, overly high fer­til­ity (N and P) still re­mains an is­sue on dairy and some dry­s­tock sites.

Wise use of fer­tiliser in these sys­tems can in­crease agri­cul­tural yields and main­tain nu­tri­ent bal­ance. Ex­cess fer­tiliser use can lead to degra­da­tion of water and air qual­ity, bio­di­ver­sity, ecosys­tem ser­vices and hu­man health.

Sur­pris­ingly, about half the dry­s­tock sites were out­side tar­get ranges for macro­p­oros­ity (al­most all be­low the tar­get range).

Ad­di­tion­ally, about half of sites were out­side tar­get val­ues for to­tal N (above the tar­get ranges) and one-third of sites were out­side tar­get val­ues for Olsen P (gen­er­ally be­low the tar­get range).

There ap­pears to be a di­ver­gence in land-use man­age­ment of dry­s­tock sites as the fer­til­ity mea­sure­ments (to­tal N and Olsen P) in­di­cate some dry­s­tock sites are above tar­get val­ues (pre­sum­ably in­ten­sively man­aged sites) whereas oth­ers, prob­a­bly more mar­ginal sites, are be­low tar­get val­ues, par­tic­u­larly for Olsen P. Pro­duc­tion could be im­proved by ad­di­tions of phos­phatic fer­tiliser on land with low Olsen P but the cost of the fer­tiliser and spread­ing may be un­eco­nomic at this time.

High phos­pho­rus lev­els re­main an is­sue for crop­ping and hor­ti­cul­ture sites. While only a few sites are cur­rently be­low tar­get val­ues for soil C, loss of soil car­bon may be a more press­ing is­sue than high fer­til­ity.

The coun­cil plans to con­tinue to mon­i­tor closely the soil or­ganic mat­ter, which is a key at­tribute that af­fects many phys­i­cal, chem­i­cal and bi­o­log­i­cal prop­er­ties that con­trol soil pro­duc­tiv­ity and re­sis­tance to degra­da­tion.

A tech­ni­cal re­port on Soil Qual­ity in the Waikato Re­gion is on the coun­cil’s web­site (www.waika­tore­gion.govt.nz).

Nu­mer­ous man­age­ment prac­tices can threaten soil sus­tain­abil­ity. These in­clude over­cul­ti­va­tion, un­der or over­fer­til­i­sa­tion, in­dis­crim­i­nate use of pes­ti­cides and other agri­chem­i­cals, clear­ing nat­u­ral veg­e­ta­tion, in­ten­sive farm­ing prac­tices and, very im­por­tantly, fail­ure to main­tain soil or­ganic mat­ter lev­els. Also, prac­tices which con­trib­ute to ero­sion can nat­u­rally cause soil prob­lems.

The im­pacts of poor soil man­age­ment have some­times be­come so se­vere in many parts of the coun­try that the adop­tion of sus­tain­able soil man­age­ment prac­tices is of cru­cial im­por­tance for fu­ture gen­er­a­tions.

Also, farm­ers – par­tic­u­larly dairy farm­ers – face a new en­vi­ron­men­tal is­sue with re­cent re­search show­ing some dairy soils are los­ing more car­bon and ni­tro­gen than dry stock and hill coun­try ar­eas.

Dairy farms on cer­tain (non­al­lo­phanic) soils have lost an av­er­age of one tonne of soil car­bon per hectare a year in some parts of the coun­try. Bi­o­log­i­cally ac­tive car­bon is the most im­por­tant part of the soil car­bon and how it is dis­trib­uted through the soil pro­file is equally im­por­tant. Soil car­bon is found pri­mar­ily in or­ganic forms, which make up soil or­ganic mat­ter.

Man­age­ment prac­tices that in­crease in-soil or­ganic car­bon, such as re­duced tillage, use of more or­ganic amend­ments and greater use of mixed farm­ing, may help to im­prove soil bio-di­ver­sity as well as soil sus­tain­abil­ity.

The Ky­oto Pro­to­col might also in­flu­ence soil sus­tain­abil­ity in the near fu­ture.

Un­der the pro­to­col, agri­cul­tural soils are high­lighted for pos­si­ble fu­ture in­clu­sion as a bio­spheric sink for car­bon. If agri­cul­tural soils were to be used as car­bon sinks, there would be a greater need and re­spon­si­bil­ity by farm­ers and land man­agers to in­crease the soil or­ganic car­bon con­tent of their soils.

Car­bon con­cen­tra­tion in New Zealand ap­pears to be rang­ing from 100 to 200 tonnes/ha.

It has been es­ti­mated if soil car­bon in­creased by 0.2 per cent on the coun­try’s 14 mil­lion ha of graz­ing land that would rep­re­sent a car­bon trad­ing value of $5 bil­lion at $20 a tonne.

Soil or­ganic mat­ter helps to main­tain soil struc­ture, re­tain soil mois­ture, pre­vent ero­sion and can act as a reser­voir for nu­tri­ents and as a source or sink for car­bon.

The fur­ther de­vel­op­ment of sus­tain­able soil man­age­ment prac­tices in this coun­try clearly re­quires a mul­ti­dis­ci­plinary ap­proach to find the best so­lu­tions.

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