*Section C1: Effects of fertilizers and age of oil palm on efficiencies of N uptake and use for biomass and yield production by alley crop species.*

The fertilizers exerted significant effects on nitrogen uptake for yield production of cassava, maize and pepper strip intercropped in the alleys of 3, 4 and 6 years oil palm plot (**Table 9**). Compared with the unmanure (PuO), application of fertilizers enhanced nitrogen contents, N uptake and N yields. NPK compound fertilizer


**Table 9.**

*Effects of fertilizers and intercrops on N content and uptake, crop yields and nitrogen harvest index (NHI).*

### *Oil Palm-Based Cropping Systems of the Humid Tropics: Addressing Production… DOI: http://dx.doi.org/10.5772/intechopen.98257*

enhanced the contents, uptake and yields of N compared with other fertilizer treatments while poultry manure had varied effects on nitrogen contents, N uptake and N yields of the intercrops. The effects of ferti plus organo mineral fertilizer on N uptake and N yields of the intercrops was similar to that of poultry manure (**Table 9**). in addition, uptake and yields of N were higher for the respective sole crops of cassava, maize and pepper compared with the strip intercrops. While N content was highest for fruits of pepper, highest N uptake and N yields were found for cassava leaves and tubers for which in addition, shoot biomass was heaviest. The interaction of intercrop and fertilizer types were significant for most of the indicators of nutrient uptake measured (**Table 9**). The biomass yields were heaviest for cassava, therefore, its N uptake and N yields were higher compared with maize and pepper under application of poultry manure (**Table 9**). Fertilizer application using NPK, fertiplus and poultry manure enhanced the nutrient uptake in cassava planted in in the alleys 3, 4 and 6 years old oil palm. However, NPK produced slight increases in N uptake of cassava under 4 and 6 years old oil palm compared with other fertilizers (NPK, Ferti Plus and poultry manure). The age of oil palm fields influenced the effects of fertilizers on the uptake of nitrogen for biomass production in cassava. Nitrogen uptake for tuber production in cassava was better under 3 years old field by NPK and 4 years old by poultry manure. The fertilizers and age of oil palm affected nutrient uptake in the leaf and seed of maize. NPK and Ferti plus significantly enhanced leaf and seed nutrient uptake of maize compared to poultry manure across the ages of oil palm. The least values for N uptake were however recorded for poultry manure and highest for 3 years old oil palm. Among fertilizer treatments, least decline in effect of age of oil palm was found for 6 years old. NPK and Poultry manure had no differences in values for 4 years old palm hence enhanced nutrient uptake in leaf production. 6 years old oil palm had the least value. Close values were found fertilizer effects on leaf and seed nutrient uptake and for 3 and 4 years old oil palm which recorded the greatest effects (**Table 9**). Ferti plus and NPK enhanced the nutrient uptake in pepper leaves and fruits transplanted into 3 years old palm. NPK fertilizer influenced nutrient uptake compared to poultry manure for 3 and 4 years oil palm. Lowest fertilizer efficiency was found for 6 years old oil palm for both leaf and fruits of pepper. Ferti plus enhanced N nutrient uptake in leaf and fruits of pepper compared with other fertilizers (**Table 9**).
