SUMMARY
Penelitian yang bertujuan untuk mendapatkan informasi tentang pemupukan N dan frekuensi pemangkasan tajuk yang tepat pada tanaman ubi jalar (Ipomoea batatas (L.) Lam.). penelitian dilakukan di Kebun Percobaan Universitas Brawijaya, di Desa Jatikerto, Malang. Rancangan perlakuan yang digunakan adalah Petak Terbagi, dosis pupuk N ditempatkan pada petak utama, terdiri dari 4 taraf : (1) tanpa dipupuk N, (2) dipupuk 67,5 kg N ha-1, (3) dipupuk 135 kg N ha-1 dan (4) dipupuk 202,5 kg N ha-1. Pemangkasan tajuk ditempatkan pada anak petak, terdiri dari 4 macam : (1) tanpa dipangkas, (2) dipangkas 1 kali, (3) dipangkas 2 kali dan (4) dipangkas 3 kali. Pengumpulan data dilakukan secara destruktif meliputi luas daun, masa luas daun, panjang umbi, diameter umbi, bobot umbi per tanaman dan indeks pembagian. Uji F taraf 5% digunakan untuk menguji pengaruh perlakuan, sedangkan perbedaan diantara perlakuan didasarkan pada nilai Duncan taraf 5%. Hasil penelitian menunjukkan terjadi interaksi nyata pada luas daun, masa luas daun dan bobot umbi per tanaman. Luas daun dan masa luas daun tertinggi umumnya didapatkan pada pemupukan N dosis 202,5 kg N ha-1 dengan tanpa maupun dengan pemangkasan tajuk 1 kali. Bobot umbi per tanaman tertinggi didapatkan pada tanaman yang diberi pupuk N dengan dosis 135 kg N ha-1 dan pemangkasan tajuk 1 kali. A field reaserch that aimed to get the appropriate of N application and frequency of topping was conducted in the experimental field of Brawijaya University, located in Jatikerto village, Malang. The experimental treatments consist of four levels of N (0 ; 67.5 kg N ha-1, 135 kg N ha-1 and 202.5 kg N ha-1) and four levels frequency of topping (without topping, 1, 2, and 3 of topping). These treatments were arranged in a split plot design; N application in the main plot and frequency of topping in the subplot with three replications. Data was collected destructively including component of growth, component of yield and plant growth analysis. F test at 5% is used to determine the effect of treatments, while the average difference between treatments was referred to Duncan value at 5%. The result showed there were significantly interaction between N application and frequency of topping on component of growth and weight of tuber per plant. Combination of N application dosage 202.5 kg ha-1 and non or once topped had resulted the highest of leaf area and leaf area duration. While the highest of weight tuber per plant was obtained on N dosage 135 kg ha-1 and topping one times.