Pupuk organik penting untuk memperbaiki sifat kimia, fisika, dan biologi tanah. Penelitian ini dilakukan untuk mempelajari peran pupuk kandang sapi dalam menyumbangkan nitrogen (N) pada tanaman padi sawah dengan teknik isotop 15N. Penelitian dilakukan di tanah sawah Jayamukti, Karawang Jawa Barat. Penelitian ini menggunakan rancangan acak lengkap dengan 6 perlakuan dan 3 ulangan. Perlakuan yang diberikan adalah pupuk kandang dengan dosis 0 t ha-1, 0 t ha-1 + 300 kg N ha-1, 5 t ha-1 + 300 kg N ha-1, 10 t ha-1 + 300 kg N ha-1, 15 t ha-1 + 300 kg N ha-1, 20 t ha-1 + 300 kg N ha-1. Hasil penelitian menunjukkan bahwa aplikasi pupuk organik dengan dosis 20 t/ha disertai dengan urea 300 kg N ha-1 dapat meningkatkan hasil berat kering gabah secara nyata sebanyak 64,75% dari perlakuan kontrol tanpa pupuk kandang dan tanpa N. Aplikasi pupuk kandang sebesar 15 t ha-1 ditambah N rekomendasi berpengaruh nyata dalam meningkatkan sumbangan N berasal dari tanah pada jerami sebesar 19,98% dari perlakuan tanpa pupuk kandang + N. Penelitian ini menunjukkan bahwa pemberian pupuk kandang mampu meningkatkan sumbangan atau kontribusi hara terutama N yang berasal dari tanah pada tanaman padi sawah.

Utilization of marginal soil plays important role in improving soybean production in Indonesia. Soybean breeding program targeting high yielding varieties and tolerant to acid soils is estimated to be more cost-effective and environmentally friendly approach in improving plant productivity on acid soil. The aim of this research was to study plant response under acid soil stress and to identify tolerant and sensitive genotype which might be useful for further breeding program. The experiment was conducted using 28 soybean varieties as genetic material. The experiment was carried out in two parts, including seedling evaluation in hydroponics and plant growth evaluation in polybag using acid soil. The first experiment was arranged in factorial randomized block design, consisting of genotype, pH, and AlCl3 treatment as the factors with 5 replications. The second experiment was conducted using randomized complete block design with 5 replications to identify the plant growth in different genotype and acid soil conditions. The results showed that the low pH and high Al inhibits seedlings root growth of soybean genotypes. The estimation of STI from root and shoot dry weight suggests Detam 1 as the most tolerant genotype followed by other varieties with lower level of tolerance. Plant response was different each genotype to both seedling evaluation in hydroponics and plant growth evaluation using acid soil.

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The carrying capacity of rice plants to meet national food demand is inseparable from effective and efficient cultivation techniques. The need of rice plants for fertilizer is a recurring problem, due to the farmers' tendency to apply fertilizer, especially urea, at the excessive doses. Balanced fertilizer practice is currently a trend encouraged by the government, because the lands that receive intensive chemical fertilization rate decreased in its fertility and health. It is indicated by the low soil acidity value (tends to be acidic to acidic) and the low soil organic carbon (SOC) content (<1%). This case happens in most areas of intensive rice cultivation in Indonesia. The principle of balanced fertilization is to provide a number of nutrients in accordance with the amount of plant needs. Determining the nutrients needed by plants can be done in several ways, including by knowing the efficiency level of plants in utilizing the nutrients that are given or added to the soil. The research objective was to determine the fertilizer dosage with the optimum efficiency level for lowland rice plants. The experiment was carried out in the rice fields of Muara Experimental Station, Bogor, using Batan's mutant rice variety and mutant line, and national rice variety as a comparison. Randomized Complete Block Design in factorial pattern was using in the experiment. As the first factor is rice variety, consisting of 3 levels factors: 1). Sidenuk mutant rice; 2). mutant line rice; and 3). Ciherang national rice variety. While the dose of urea as second factor consists of 4 levels: 1). no urea fertilizer; 2). urea at a dose of 100 kg N / ha; 3). urea at a dose of 200 kg N / ha; and 4). urea at a dose of 300 kg N / ha. Stable isotope techniques 15 N is used to determine the efficiency of nitrogen uptake by rice plants. The results showed that the highest nitrogen use efficiency of rice varieties owned by Sidenuk amounted to 22.76%; Ciherang variety was 22.30%; and the mutant lines were 17.19%. This efficiency was obtained from the application of urea fertilizer at a dose of 100 kg N / ha (Sidenuk and Ciherang) and 200 kg N / ha (mutant lines).