The erosion plot method for direct evaluation in agriculture became necessary to (1) quantify soil erosion on cocoa, areca and oil palm, (2) determine the most effective soil conservation, and (3) calculate nutrient content in sediment. The experiment was treated with three conservation practices and the conventional treatment as control in a completely randomised block design. The results showed for the areca land use, that soil conservation with ridges + maize produced the lowest erosion (1.68 t/ha). For cocoa land use, the ridges + groundnut treatment produced the lowest erosion (8.2 t/ha). For oil palm land use, the cover crop of Mucuna bracteata had lowest erosion yield (12.2 t/ha). Soil conservation techniques significantly affected the levels of organic C and available P under the cocoa land use, where ridges + maize have the lowest content of organic C and available P in soil sediment (1.03% and 0.69 ppm). Soil conservation at areca land use also has a significant effect on the levels of organic C and available N, but it did not affect significantly the levels of available P and exchangeable K sediments, where ridges + groundnut have lowest organic C and available N in sediment (1.4% and 0.18%). Furthermore, soil conservation on the land use of oil palm showed a significant effect on the levels of available P, but did not significantly affect the levels of organic C, available N and exchangeable K sediments. Soil conservation with cover crops Mucuna bracteata showed the lowest available P in sediments (0.86 ppm).

Daerah Aliran Sungai (DAS) mengalami peningkatan kerusakan akibat hubungan dan interferensi manusia yang berdampak pada kesetimbangan hidrologi sehingga terjadi bencana. Bencana banjir yang merupakan bencana hidrologi rutin terjadi di DAS Jambo Aye. Penelitian ini bertujuan untuk menganalisa hubungan karakteristik hidrologi DAS Jambo Aye terhadap potensi dan kejadian banjir di wilayah DAS Jambo Aye. Karakeristik kemiringan lereng, pergerakan tanah, analisis kelompok hidrologi tanah (HSG), Antecedent Precipitation Index (API) dan kurva limpasan digunakan sebagai indikator hidrologi untuk mengidentifikasi potensi banjir yang terjadi di DAS Jambo Aye. Analisis menunjukkan DAS Jambo Aye termasuk wilayah yang berpotensi mengalami banjir. Potensi banjir genangan terdapat di wilayah hilir yang mempunyai karakteristik lereng landai (12%), kapasitas infiltrasi sangat lambat (37,95%), nilai kurva limpasan tinggi (17%) dan tingkat kebasahan yang tinggi (26%). Banjir bandang berpotensi terjadi di wilayah hulu yang mempunyai karakteristik lereng curam, adanya pergerakan tanah dan curah hujan yang tinggi. Pengelolaan DAS perlu dilakukan di DAS Jambo Aye mengingat kejadian banjir yang sering terjadi.

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.