We used a space for time substitution approach (chronosequence) to quantify the long-term impacts on biomass and soil properties, including changes in SOC stocks and soil chemical fertility characteristics, following pasture conversion into OP plantations. As we aimed to study the long-term effects of OP cultivation on soil properties, OP plots with palm stands passing by the first rotation cycle (up to 30 years) and the second rotation cycle (new palms transplanted after the first cycle) were considered. We selected six OP plots that range from 12 to 56 years after pasture conversion and three reference pasture sites. All OP plots were part of a large-scale OP plantation. This large-scale OP farm could have the longest history of OP cultivation in the whole Llanos region, and its management is representative of the typical management of OP plantations in this region of Colombia. The reference sites were cattle ranching farms that were adjacent to the sampled OP farm. The primary criterion for selecting OP plots was the existence of pastures as the sole preceding land-use. This information was obtained by direct communication with the personnel in charge of both the OP farm operation and the neighboring cattle ranching farms. In addition, in the plot selection process, sites with steep slopes, inundated parts, or located on floodplains and with distinct management to the general farm practices were excluded. OP plots were planted in a triangular design 9 m apart, which resulted in a density of 143 palms ha−1. All OP plots, except the recently replanted 32-year plot, presented four well distinct management zones: (i) the frond piles located in between palms and where pruned OP fronds are accumulated; (ii) the harvest path, which is the area of traffic for mechanized operation, i.e., fruit harvesting, in between parallel palm lines; (iii) weeded circle, which is an area around the palm trunk of about 5 m in diameter where most fertilizer inputs are placed up until 5 to 6 years; and (iv) the interrow where almost no field operations takes place and scattered understory vegetation, i.e., weeds, grows. Land was prepared prior plantation establishment by chisel plow to a depth of 10 to 15 cm. Dolomitic lime was added to increase soil pH. Fertilization practices were the typically recommended ones for the region and were done periodically every year in two applications on the weeded circle at young ages or broadcasted all over the plantation except the harvest path in mature plantations (over 5-year plantations). Nitrogen (N), phosphorus (P), and potassium (K) fertilization of 150 to 725 kg ha−1 year−1 were applied depending on palm stand age, i.e., 725-kg NPK-complete fertilizer applied to plantation aging more than 10 years. Other nutrients including boron and magnesium were also applied regularly every year.

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