Citric acid is an organic acid naturally present in fruits, one of the ingredients that can be used as a retarder in a concrete mixture. As retarder serves to slow the timing of concrete hardening. In the implication the use of this material affects the time of hardening and compressive strength, therefore need a better control to get the optimal value. The test sample used was 36 with variation of addition of citric acid 0%, 0.15%, 0.3%, 0.45% for the weight of cement. The results obtained the greater the addition of citric acid the longer the hardening of concrete and the greater workability of concrete. The maximum value of compressive strength of concrete is in the addition of 0.15% citric acid with an increase in compressive strength of 82.2% of the nominal concrete.

The use of Information and Communication Technologies (ICT) in a variety of educational activities creates lots of conveniences, increases effectiveness and efficiency. It is believed that the use of ICT in the educational process makes learning more interesting, enables explaining the concept more clearly, foster creativity, collaborative skills and many more. Due to the fact that the students are millennial generation, who is quite familiar with ICT in their daily life, the use of ICT is important. In learning mathematics, GeoGebra which is dynamic open source software can be used as a teaching and learning tool for mathematics. However, some are still unaware of the benefits of using GeoGebra to learn mathematics. This article discusses the various benefits of using GeoGebra in mathematics teaching and learning, and several studies that support it. The advantages of using GeoGebra in mathematics teaching and learning are as follows: GeoGebra might be used to demonstrate or visualize mathematical concepts, as well as a means of constructing mathematical concepts. The use of GeoGebra in mathematics learning can foster mathematical reasoning, creativity, support collaboration, involve students more in the learning process. And, the more involved, more effective and efficient the learning is.

The conversion of peat soils to agricultural uses has been thought to increase CO2 emission due to several factors, including fertilization. However, evidence on the effect of fertilization on CO2emissionsfrompeat soils is rareand often inconsistence. We measured the effects of different types of fertilizer, including N, P and K sources, and clay as an ameliorant on CO2 emission from a bare peat soil in Lubuk Ogong, Riau Province. Nutrients were added in the following combinations: 0 (unfertilized plot), N source (urea), slow-release N (slow release urea), N and Psource (Urea+SP-36), N, P and K sources (urea+SP-36+KCl) and combined NPK-Clay. Fertilization resulted in a decreasein CO2 emissions compared to that prior to fertilization except when slow-release urea was applied. Decreasing of CO2 emissions was probably due to pH-related effects because the pH in the N treatment was lower than in both the control and the unfertilized plot. A decreasein the level of CO2 emissions among the treatments followed the order NPK-Clay>NP>NPK>urea>slow-release urea. Covariance analyses showed that the difference in CO2 emissions prior to treatment was not significant. The application of individual and combined treatments of N, P, K and NPK mixed with 5 Mg ha-1 clay led to significantly reduced CO2 emissions from bare peat soil in Lubuk Ogong, Riau Province. In addition to fertilization, the water table depth was the only parameter that significantly affected the CO2 emissions (P<0.05). We conclude that the application of nutrient combinations, including N, P, K and clay, could reduce CO2 emissions because these treatments maintain a balanced nutritional condition in the soil with respect to the microbial activity.Keywords: Amelioration, CO2 emission, fertilization, tropical peat soils

Aflatoxin is secondary metabolite produced by Aspergillus flavus and A. paraciticus that grow on the seed coat (testa) of groundnut. This toxin is a serious food safety issue throughout the world. The availability of resistant genotype to A. flavus infection and/or aflatoxin contamination urgently needed. The experiment found one genotype had aflatoxin contamination under the safe level (≤ 10 ppb), with <15% of seed number infected by A. flavus. Recently, the biggest peanut industry, where the main production is roasted-peanut (in shell) produced from fresh pods, grows and develops that variety.

No abstract

Penelitian pelindian dan serapan logam berat oleh tanaman jagung yang dipupuk dengan pupuk gambut (Pugam) dilakukan dalam bentuk percobaan pot di rumah kaca. Penelitian bertujuan untuk menguji laju pelindian dan serapan logam berat oleh tanaman jagung yang dipupuk dengan Pugam pada tanah gambut. Penelitian menggunakan rancangan acak kelompok dengan lima perlakuan yaitu kontrol, NPK konvensional, dan dosis Pugam 15 g pot -1 , 30 g pot -1 , dan 45 g pot -1 atau setara dengan 500 kg, 1000 kg, dan 1500 kg ha -1 . Jumlah logam berat yang terlindi dapat dideteksi dari konsentrasi logam pada air licit (leachate) yang diambil secara reguler dari dasar pot, sedangkan serapan logam berat diukur melalui analisis tanaman. Hasil penelitian menunjukkan bahwa Pugam mengandung sejumlah logam berat yaitu Cr, Pb, dan Cd dalam konsentrasi yang rendah, yaitu berturut-turut 96; 17,3; dan 1,6 mg kg -1 . Sebagian dari logam berat tersebut terdeteksi pada air licit dari tanah gambut yang diberi perlakuan Pugam, namun konsentrasinya di bawah nilai ambang batas konsentrasi logam berat untuk tanaman pertanian seperti yang tercantum pada lampiran PP. 82/2001 tentang kualitas air. Logam berat Cr dan Cu cukup banyak terdeteksi pada pupuk Pugam, yaitu masing masing 96 mg kg -1 dan 1546 mg kg -1 , tetapi tidak terdeteksi pada air licit, karena kedua logam berat ini memiliki afinitas yang tinggi untuk berikatan dengan ligan organik. Logam berat Pb, As, Se, dan Zn mengalami pelindian yang terdeteksi melalui air licit, tetapi konsentrasinya berada di bawah nilai ambang batas kualitas air (PP No. 82/2001) dan tidak berkorelasi dengan perlakuan pupuk Pugam. Bobot masa akar dan biomas pada perlakuan Pugam 500 kg ha -1 meningkat masing-masing 58 kali dan 45 kali lipat dibandingkan dengan perlakuan NPK karena Pugam bila larut melepaskan kation polivalen yang mampu menetralisir asam fenolat yang beracun bagi tanaman. Perlakuan Pugam tidak meningkatkan konsentrasi dan serapan logam berat oleh tanaman jagung. Kisaran konsentrasi logam berat adalah (mg kg -1 ) 1,95-2,79 Pb; 0,2-0,3 As; 1,45 -2,83 Cr; 0,05 Co, sedangkan Cd, Hg, dan Ni tidak terdeteksi. Semua kisaran konsentrasi logam berat tersebut jauh di bawah nilai ambang batas konsentrasi yang membahayakan.