Abstract. Satriawan H, Fuady Z. 2019. Analysis of weed vegetation in immature and mature oil palm plantations. Biodiversitas 20: 3292-3298. The species of weeds which grow and dominate in palm oil areas depend on location, local climate, and the light received. This research aimed to determine the diversity of weeds in the planting of palm oil with a different age grown in 2012, 2013, 2014 and 2016. The sample slots measured uniformly at 1 m x 1 m totaling 25 plots. Vegetation analysis was conducted to the density (D), relative density (RD), frequency (F), relative frequency (RF), important value index (IVI), Summed Dominance Ratio (SDR), and Species Diversity Index (H’). Weed composition includes 21 families with 36 species, with the total number of each individual during the year of palm oil planting was 3540, 3148, 3731, and 2910. The relative density value of the highest weeds in the planting year group in 2012 and 2013 were Asystasia intrusa (20.22% and 21.05%), in 2014 were Eleusine indica (23.93%) and 2016 were Cynodon dactylon with 24. 49%. The importance value of weeds in four groups in planting year of oil palm was also in line with the relative density value. These were A. intrusa in 2012 and 2013, amounting to 27.41 and 27.95 and in 2014 and 2016, totaling to 23.72 and 37.64 was E. indica and C. dactylon. The value of the highest species diversity of 6.85 was found in the year 2014, followed by 2012 with 5.88.

In Indonesia, agricultural land for oil palm plantation is mostly placed on slope areas. Erosion carries down surface soil layers which are generally fertile and rich in organic matter and nutrients, causing the loss of plant nutrients. Cover crops provide protection against the destruction of soil aggregates by rain and runoff. This research aims to study the effectiveness of vegetation as soil conservation in controlling erosion and runoff. This study was a field experiment on erosion plots of 10 m × 5 m with 1-2-year-old oil palm trees planted on a 15-40% slope, which were arranged in a Split Plot Design with replications as blocks, consisting of a combination of two factors: the age of the oil palm and slope as the first factor, and conservation techniques as a second factor. The results showed that the soil conservation techniques in oil palm cultivation could reduce the rate of surface runoff, soil erosion and nutrient loss. Soil conservation with upland rice -soybean -Mucuna bracteata, in sequence (T3) in oil palm 7-25 months old and 15-25% slopes (P1) were most effective reduced runoff, increase the infiltration and preventing soil erosion and nutrient loss in all age of oil palm and slope of land.

Currently, many have been concerned with the oil palm cultivation since it may also put land resources in danger and bring about environmental damage. Poor practices in managing agricultural land very often occur due to the inadequate knowledge of soil conservation. Application of soil and water conservation is to maintain the productivity of the land and to prevent further damage by considering land capability classes. This research was aimed at obtaining soil and water conservation techniques which are the most appropriate and optimal for oil palm cultivation areas based on land capability classes which can support sustainable oil palm cultivation. Several soil conservation techniques had been treated to each different class III, IV, and VI of the studied area. These treatment had been performed by a standard plot erosion. The results showed for the land capability class III, Cover plants + Manure was able to control runoff, erosion and reduce leaching of N (LSD P≤0,05), in which soil conservation produced the lowest erosion (3,73t/ha), and N leaching (0,25%). On land capability class IV, Sediment Trap + cover plants+ manure was able to control runoff, erosion and reduce organic C and P leaching (LSD P≤0,05), in which soil conservation produced the lowest runoff (127,77 m 3 /ha), erosion (12,38t/ha), organic C leaching (1,14 %), and P leaching (1,28 ppm). On land capability class VI, there isn't significant effect of soil conservation, but Bench Terrace + cover plants +manure has the lowest runoff, erosion and soil nutrient leaching.

Abstract. Satriawan H, Fuady Z, Ernawita. 2020. The potential of Asystasia intrusa weed as a cover crop in oil palm plantations. Biodiversitas 21: 5711-5718. Weeds generally found in oil palm plantations, one of which is dominant is Asystasia intrusa. This weed has begun to be used as a cover crop on oil palm land because it is assumed to have a beneficial effect. The purpose of this research is to explore the potential of Asystasia intrusa in growing as a cover crop on oil palm plantations. The experimental arrangement used was split-plot design. Oil palm plan’s ages were used as the main plot, while the spacing plant (Asystasia intrusa) as the subplots. Experiments were done in triplicate. The results showed that Asystasia intrusa has the potential to be used as a cover crop in oil palm plantations, since it meets several requirements, such as quickly covering the land (12 WAP), fast decomposing (30-60 days), tolerance to shade. This was indicated by the growth percentage of 97.56%, containing nutrients N (1.65-1.77%), P (0.29%), and K (4.6-4.97%), as biomass (0.9 t C/ha/year) and soil carbon stocks (39.52-41.16 t/ha/year). The studied weed also has the ability to increase soil carbon stock up to 119%.

ABSTRACT

Abstract. Satriawan H, Fuady Z, Ernawita. 2021. The potential of Nephrolepis biserrata fern as ground cover vegetation in oil palm plantation. Biodiversitas 22: 4808-4817. Nuisance plants or weeds are commonly found in agricultural landscapes including in oil palm plantations. Despite being considered as weeds, several of them have the potential to be used as ground cover vegetation including Nephrolepis biserrata (Sw). Schott. This fern species exhibits beneficial characteristic as ground cover plant especially in terms of the contribution of organic matter and soil moisture through the prevention of evapotranspiration. The objective of this research is to explore the potential of N.biserrata as ground cover vegetation in oil palm plantations based on the assessment of its ecological characteristics regarding the growth and decomposition rate, tolerance to shade, organic contents and carbon accumulation. The split plot experimental design was used with the age of oil palm plants was used as main plot while in the sub-plots the spacing of N. biserrata was used at three varying distances 10x10cm, 20x20 cm, and 30x30 cm, each treatment had three replicates. Nine parameters observed were the percentage of growth, the percentage of ground cover, plant height, fronds number per plant, leaves number per plant, Leaf Area Index, dry weight (g), nutrient content in plant tissue, and potential carbon stock. Results showed that N. biserrata showed rapid growth in covering the ground surface (8-12 weeks after planting), had rapid decomposition rate (30-60 days), tolerant to shading which was characterized by the highest percentage of growth up to 81.16% and covering area up to 95.9%, accumulated organic contents of N (1.23-1.53%), P (0.18-0.22%), and K (1.4-1.67%), respectively. In addition, total dry weight biomass obtained was 27.1 ton/ha, accumulated carbon in plant of 0.9 tons C/ha/year, and amount of soil carbon stock 76.4-97.4 tonnes/ha/year. The results of this study suggest that Nephrolepis biserrata is a potential plant to be utilized as a ground cover plant in oil palm plantations.

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Large plantations such as oil palm plantations are usually covered by several weed species which occasionally function as a land cover. Soil samples were obtained through Simple Random Sampling on various types of ground cover weeds, e.g Asystasia intrusa, Eleusine indica, Cyperus kyllingia Endl. and Cyrtococcum oxyphyllum Stapf., in 7-year old oil palm stands, and Asystasia intrusa, Cyperus kyllingia Endl., Cyrtococcum oxyphyllum Stapf. and Cyperus rotundus, in 6-year old stands. Each sample was randomly obtained from each replicate plot at a depth of 0-20 cm (layer 1) and 20-50 cm (layer 2) at 5 points. Variables of soil chemical properties observed were N-total, P-available, K-total, C-organic and soil pH, while the physical properties observed were water content (%) and volume weight, using the gravimetric method. The results showed that the presence of weeds beneath the oil palm stands in plantation areas did not continuously have a negative effect on the growing environment. In this study, the presence of 4 (four) weed species under 6 and 7 years old were found around old oil palm stands and classified as dominant existences actually have a positive tendency to influence the quality of physical and chemical properties of soil under oil palm stands.