Judul: Consistency and Shrink-Swell Soils in Shallot Field, Brebes Regency, Central Java
Abstrak: Bawang merah merupakan salah satu komoditas yang sangat dibutuhkan dalam kehidupan sehari-hari. Sentra produsen bawang merah terbesar di Indonesia adalah Kabupaten Brebes. Namun pada kenyataannya produktivitas bawang merah di Kabupaten Brebes mengalami penurunan. Salah satu upaya untuk meningkatkan produktivitas bawang merah yaitu dengan melakukan pengolahan tanah yang baik, misalnya dengan mengkaji konsistensi tanah di lahan tersebut. Kemampuan mengembang dan mengerut tanah yang tinggi dapat beresiko terhadap pertumbuhan umbi bawang merah. Resiko tersebut dapat diminimalisir dengan cara memperhatikan nilai COLE (Coeficient Of Linear Extensibility) yang merupakan indikator dalam penetapan sifat mengembang dan mengerut tanah. Penelitian ini bertujuan menganalisis konsistensi dan nilai COLE serta kaitannya dengan sifat fisik dan kimia tanah pada lahan bawang merah di Kabupaten Brebes, Jawa Tengah. Hasil penelitian menunjukkan bahwa Konsistensi dan Nilai COLE tanah berbeda antar jenis tanah. Indeks plastisitas, jangka olah, dan nilai COLE memiliki korelasi terhadap kadar klei dan bahan organik. Ketiga jenis tanah memiliki Indeks plastisitas yang tinggi, jangka olah yang sempit, dan nilai COLE yang baik. Hal ini menunjukkan kualitas tanah pada lahan ini masih perlu diperbaiki untuk memperoleh kondisi yang lebih baik bagi pertumbuhan bawang merah., Shallots are one of the commodities needed in everyday life. The largest shallot producing center in Indonesia is Brebes Regency. But in reality, shallot productivity in Brebes Regency has decreased. One of the efforts to increase shallot productivity is by doing good tillage, for example by assessing the consistency of the soil. The high ability of soil to swell and shrink can be a risk to the growth of shallot bulbs. This risk can be minimized by paying attention to the COLE (Coeficient Of Linear Extensibility) value which is an indicator in determining the soil swelling and shrinking. This study aims to analyze the consistency and value of shrink-swell soil and its relation to the soil physical and chemical properties on shallot fields in Brebes Regency, Central Java. The results showed that soil consistency and shrink-swell value were different among soil types. Plasticity index, tillage period, and shrink-swell value have a correlation with clay and organic matter content. All three soil types have high plasticity index, narrow tillage period, and good shrink-swell value. This shows that the quality of the soil on this land still needs to be improved to obtain better conditions for the growth of shallots.
Keyword: gleisol, cambisol, mediteran, productivity

Judul: Critical Limit Phosphorus of Shallot Plants on Soil in Brebes Regency, Central Java
Abstrak: Intensifikasi pemupukan yang berimbang merupakan salah satu cara untuk meningkatkan mutu bawang merah dan produksi guna memenuhi permintaan pasar. Guna mencapai hasil panen yang optimal, ketersediaan fosfor (P) tanah harus berada di atas tingkat kritis. Penelitian ini bertujuan menentukan batas kritis hara P di tanah-tanah Brebes untuk bawang merah, menentukan pengekstrak terbaik untuk bawang merah dan mengevaluasi pengaruh pemupukan P terhadap pertumbuhan dan produksi tanaman. Penentuan batas kritis P di tanah dilakukan dengan mengekstrak P tanah dari 16 lokasi yang tersebar di Kabupaten Brebes. Pemupukan P dilakukan dengan pemberian larutan KH2PO4 sebanyak 0, ½X, X, dan 2X dimana X adalah dosis pupuk P anjuran dalam bentuk P2O5 sebesar 120 kg ha-1. Tanaman dipanen biomasanya berumur enam minggu setelah tanam. Batas kritis P tanah ditetapkan menggunakan metode Cate dan Nelson. Hasil penelitian menunjukkan bahwa tiap ekstraksi P memiliki nilai koefisien korelasi berbeda yang dipengaruhi oleh pengekstraknya. Koefisien korelasi antara kandungan hara P tanah yang diekstrak menggunakan metode Bray 1, Olsen, Mehlich I, dan HCl 25% dengan bobot kering tanaman berturut-turut adalah 0,630, 0,341, 0,821, dan -0.089. Nilai korelasi untuk metode Bray 1 dan Mehlich 1 dengan bobot kering tanaman secara statistik berturut-turut nyata dan sangat nyata. Batas kritis kandungan P tanah untuk mencapai 90% produksi relatif bawang merah di kabupaten Brebes tersebut berdasarkan metode Bray I, dan Mehlich I 40 ppm P. Pengekstrak P tanah di Brebes yang paling baik adalah Mehlich 1. Pemupukan disarankan pada tanah-tanah dengan kadar P tanah kurang atau sama dengan 40 ppm P, Intensification of balanced fertilization is one way to improve shallot quality and production to meet market demand. In order to achieve optimal crop yields, soil phosphorus (P) availability must be above a critical level. This study aimed to determine the critical level of P in Brebes soils for shallots, determine the best extractant for shallots and evaluate the effect of P fertilisation on plant growth and production. Determination of the critical level of P in the soil was determined by extracting soil P from 16 locations spread across Brebes Regency. P fertilisation was carried out by applying KH2PO4 solution as much as 0, ½X, X, and 2X where X is the recommended dose of P fertiliser in the form of P2O5 of 120 kg ha-1. The plants were harvested six weeks after planting. The critical level of soil P is determined using the Cate and Nelson method. The results showed that each P extraction had different correlation coefficient values influenced by the type of extractants. The correlation coefficients between soil P nutrient content extracted by Bray 1, Olsen, Mehlich I, and HCl 25% methods and plant dry weight were 0.630, 0.341, 0.821, and -0.089, respectively. The correlation values for Bray 1 and Mehlich 1 methods with plant dry weight were statistically significant and highly significant, respectively. The critical limit of soil P content to achieve 90% of relative yield of shallots in Brebes district based on Bray I, and Mehlich I methods were 40 ppm P. The best soil P extractant in Brebes was Mehlich 1. Fertilisation was recommended on soils with soil P content
Keyword: Biomass, Cate and Nelson, Correlation, Relative yield

Judul: Comparison of HIV Model with and without Time Delay
Abstrak: Acquired immunodeficiency syndrome (AIDS) is the reduction of the human immune system. AIDS is caused by human immunodeficiency virus (HIV). No medicine has been found for this desease until recently. An AIDS therapy is usually performed with highly active antiretroviral therapy, namely reverse transcriptase inhibitors, protease inhibitors and combination of both. Various models have been developed to explain the immune system of patients with AIDS, namely the HIV, response and the time delay model. This paper discusses the comparison between the dynamics of the HIV virus, the dynamic response of protease inhibitors and dynamics of time delay. The dynamics model of HIV is influenced by the level of white blood cells produced and the rate of its death. Dynamics of protease inhibitors on the response and the time delay model is influenced by the death rate of infected white blood cells and the failure rate of treatment.
Keyword: