Dr Gaius Eu­dox­ie

Soils have been spot­light­ed for their cen­tral role in ad­dress­ing glob­al threats, in­clud­ing cli­mate change and food se­cu­ri­ty. Soils play an im­por­tant role in the cy­cling of el­e­ments es­sen­tial to life.

They sup­ply all plant es­sen­tial el­e­ments but the ba­sic macro el­e­ments Car­bon, Oxy­gen and Hy­dro­gen, fa­cil­i­tat­ing 95 per cent of glob­al food pro­duc­tion. How­ev­er, not all soils pro­vide all re­quired el­e­ments at all times. Mul­ti­ple threats to soils, such as ero­sion, acid­i­ty, and nu­tri­ent im­bal­ance, add lay­ers of com­plex­i­ty to main­tain­ing health, qual­i­ty and sup­port­ing func­tions in food pro­duc­tion and cli­mate re­silience.

Lo­cal soils have poor health, char­ac­terised main­ly by low or­gan­ic car­bon con­tent and acid pH. Tra­di­tion­al­ly, syn­thet­ic fer­tilis­ers and ma­nures have been used to im­prove pro­duc­tiv­i­ty.

While these ap­proach­es have mer­it, lit­tle at­ten­tion is placed on site con­di­tions and best prac­tices to op­ti­mise the ex­pect­ed pos­i­tive re­sponse. The large vari­abil­i­ty in soil prop­er­ties across the coun­try war­rants a more de­tailed analy­sis of spe­cif­ic farmer and com­mu­ni­ty grow­ing con­di­tions. The need for and use of soil test­ing is fun­da­men­tal.

Ar­guably, farm­ers are aware of the im­por­tance of test­ing to sup­port cul­ti­va­tion but are re­luc­tant to en­gage or are not con­fi­dent in the out­come. The re­sults are poor soil fer­til­i­ty prac­tices, low pro­duc­tiv­i­ty, low nu­tri­tion­al qual­i­ty, nu­tri­ent min­ing, en­vi­ron­men­tal pol­lu­tion and soil degra­da­tion. It is not un­usu­al to hear farm­ers com­plain of re­duced soil pro­duc­tiv­i­ty, even un­der in­tense fer­til­i­sa­tion.

Man­ag­ing soil fer­til­i­ty and, by ex­ten­sion, crop nu­tri­tion is com­plex and tech­ni­cal­ly chal­leng­ing for most farm­ers. Restor­ing con­fi­dence and en­sur­ing qual­i­ty in sup­port­ing in­sti­tu­tions is fun­da­men­tal to man­ag­ing soil for nu­tri­tion.

Ev­i­dence shows that av­er­age yields for many veg­etable and field crops are < 50 per cent of po­ten­tial yields even un­der high in­put lev­els. In­ad­e­quate soil fer­til­i­ty and crop nu­tri­tion man­age­ment con­tribute to low yields and nu­tri­tion­al­ly poor foods. Re­search at The UWI on cas­sa­va pro­duc­tion showed that rais­ing the soil pH to six re­sult­ed in a 100 per cent in­crease in yield. When com­bined with tar­get­ed nu­tri­ent man­age­ment (ap­pli­ca­tion of 100kg N/ha), the in­creased yield is ap­prox­i­mate­ly 2.5 times greater and has a longer shelf life.

Lim­ing is fun­da­men­tal to ad­dress­ing soil acid­i­ty and nu­tri­ent avail­abil­i­ty. With the larg­er por­tion of Trinida­di­an soils clas­si­fied as mod­er­ate­ly to strong­ly acid and not­ing the sug­ar cane plan­ta­tion his­to­ry, ame­lio­ra­tion should be as rou­tine as land prepa­ra­tion.

The 4Rs of nu­tri­ent stew­ard­ship in­clude right source, right rate, right fre­quen­cy and right place­ment and present a sim­ple frame­work for us­ing fer­tilis­ers and amend­ments. Source and rate con­sid­er­a­tions are linked to soil test­ing. The lo­cal norm is over-ap­pli­ca­tion (of­ten not mea­sured) of nu­tri­ents week­ly. This con­tributes to soil degra­da­tion and re­source pol­lu­tion. The tim­ing of nu­tri­ent in­puts should com­ple­ment crop de­mand to en­cour­age up­take and util­i­sa­tion. Nu­tri­ent up­take pat­terns have not been de­ter­mined for lo­cal crops, but the con­cept of “root­ing”, “grow­ing”, and “bear­ing” salts is in­ad­e­quate for op­ti­mis­ing yield.

Ad­just­ing fer­tilis­er place­ment is the eas­i­est win for farm­ers and per­haps the one with the great­est po­ten­tial im­pact. Un­der lo­cal con­di­tions, “top dress­ing” or oth­er vari­a­tions of fer­tilis­er place­ment on the soil sur­face is very in­ef­fi­cient, par­tic­u­lar­ly for phos­pho­rus and potas­si­um with low to mod­er­ate mo­bil­i­ty in soils. Deep place­ment (10 cm be­low the propag­ule as a basal ap­pli­ca­tion) or spot ap­pli­ca­tion with in­cor­po­ra­tion (buried five to ten cm next to the plant) is rec­om­mend­ed to en­cour­age ear­ly root es­tab­lish­ment and veg­e­ta­tive growth.

Or­gan­ic amend­ments have a spe­cial role in trop­i­cal soils, pro­vid­ing ben­e­fits be­yond nu­tri­ent sup­ply. Sta­ble or­gan­ic amend­ments (eg, com­posts) have the po­ten­tial to feed the crop as well as the soil. Nour­ish­ing the soil is im­por­tant, as trop­i­cal soils have poor health. Not on­ly do com­posts re­cy­cle nu­tri­ents and fa­cil­i­tate cir­cu­lar­i­ty, they al­so keep car­bon in the soil. Farm­ers pro­duce tons of bio­mass per sea­son that oth­er­wise is lost to the at­mos­phere and con­tributes to green­house gas emis­sions. Pro­grammes en­cour­ag­ing on-farm com­post­ing and bio­mass reuse are im­por­tant food and nu­tri­tion se­cu­ri­ty el­e­ments.    

The “one health” prin­ci­ple teach­es bet­ter soils for bet­ter plants for bet­ter an­i­mals with fi­nal stage ben­e­fits to hu­mans. The mantra recog­nis­es the mul­ti­di­men­sion­al na­ture of con­nect­ing liv­ing sys­tems. As the coun­try ex­pands its ef­forts at in­creas­ing food pro­duc­tion and en­sur­ing food and nu­tri­tion se­cu­ri­ty, the role of in­sti­tu­tions pro­vid­ing de­vel­op­ment sup­port must be cen­tre stage. A new mod­el of co­op­er­a­tive ex­ten­sion and tech­nol­o­gy trans­fer is need­ed to at­tain these goals. The Fac­ul­ty of Food and Agri­cul­ture at The UWI has re­spond­ed to the need for di­ag­nos­tic test­ing by es­tab­lish­ing the Agro-en­vi­ron­men­tal Ser­vices Unit and con­tin­ues to fo­cus on in­no­v­a­tive and re­silient soil man­age­ment.