Long-term mineral fertiliser use and maize residue incorporation do not compensate for carbon and nutrient losses from a Ferralsol under continuous maize?cotton cropping

KINTCHÉ, K.,; GUIBERT, H.,; SOGBEDJI, J.M; LEVÊQUE, J.,; BONFOH, B.,; TITTONELL, P.

FIELD CROPS RESEARCH

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2016 vol. 184 p. 192 - 200

0378-4290

It has been repeatedly argued that mineral fertiliser application combined with in situ retention of cropresidue biomass can sustain long-term productivity of West African soils. Using 20-year experimentaldata from southern Togo, a biannual rainfall area, we analysed the effect of two rates of mineral NPKfertiliser application to maize?cotton rotation on the long-term dynamics of soil C and nutrient contents,as compared with two control treatments. Mineral fertiliser treatments consisted of application to bothmaize (first season) and cotton (second season) the research-recommended NPK rates (Fertiliser-RR)and 1.5 times these rates (Fertiliser-1.5 RR). Control treatments consisted of cropping maize and cottonwithout fertiliser use (No-Fertiliser) and of double annual soil tillage (as done for planted treatments)without planting a crop (Tillage-NoCrop). Maize residue biomass was every year returned to the soil ofcrops planted treatments, whereas cotton stems were uprooted, piled and burnt on the experimentalplots as done locally for phyto-sanitary reasons. Treatment effects were analysed through a long-termchange in crop productivity, in soil C and nutrient contents. Our results indicate that productivity of maizeand notably of cotton cannot be sustained in this Ferralsol without nutrient inputs. On average, maizeyields without fertilisers decreased from 2 t ha−1after woodland clearing to 0.5 t ha−1after 10 years ofcultivation, while cotton yields decreased from 1.5 to 0.5 t ha−1only after 5 years. In spite of the need ofmineral fertiliser use to sustain productivity of this soil, there was little justification to increase inputs ofmineral fertiliser over the research recommended rate. Over 20-year experiment, both maize and cottonwhile received N, P and K inputs at the research-recommended rates produced virtually the same yields aswhen these rates were increased by 50%. Although C inputs to soil under RR and 1.5 RR were greater than inthe No-Fertiliser control (nil for Tillage-NoCrop), and the N input was more favourable for 1.5RR, the ratesin which contents of soil C and N decreased over time did not differ substantially between treatments.Soil available P decreased for all treatments, while exchangeable K concentration increased under RRand 1.5 RR and decreased in unfertilised treatments (No-Fertiliser and Tillage-NoCrop). In fertilised plotsand in tillage no-planted plots, soil pH decreased more than in No-Fertiliser plots. A decline of soil pHwas associated with a decline of exchangeable Ca and Mg, which were on average 20 and 40% higherin fertilised plots than in No-Fertiliser plots. We conclude that soil C and N decline in this Ferralsol wasmore determined by a change in soil conditions due to woodland clearance and continuous tillage thanby the quantities of C or N inputs added annually.