POSISI CONTOH DAUN UNTUK ANALISIS STATUS FOSFOR (P) PADA BIBIT JARAK PAGAR (Jatropha curcas L.) DAN KADAR P TERSEDIA PADA DAERAH PERAKARANNYA
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Pusat Penelitian dan Pengembangan Perkebunan
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ABSTRAKStatus P pada tanaman dapat diduga dengan menganalisis kadar Ppada daun, karena daun merupakan suatu bagian tanaman yang sangataktif. Untuk itu, diperlukan informasi posisi daun yang sesuai untukdijadikan contoh daun untuk analisis status P tanaman. Percobaan inibertujuan untuk menentukan posisi daun yang sesuai untuk analisis statusP dan mempelajari perbedaan antara kadar P tersedia di tanah dan dirhizosphere, serta hubungannya dengan kadar P daun bibit jarak pagar.Percobaan dilakukan di rumah kaca Balai Penelitian Tanaman Rempahdan Aneka Tanaman Industri (Balittri) Pakuwon, Sukabumi, Jawa Barat,pada September 2006 sampai dengan Juli 2007, disusun dalam rancanganacak lengkap (RAL) dengan 3 (tiga) ulangan. Setiap unit percobaan terdiriatas 20 tanaman. Perlakuan yang diuji adalah: (a) daun ke-1 atau daunyang terletak tepat di bawah kuncup daun yang belum mekar sempurna,(b) daun ke-2 atau daun yang terletak setelah/di bawah daun ke-1, (c) daunke-3, dan (d) daun ke-4. Parameter yang diamati adalah kadar P daun (%),kadar P tersedia di tanah dan rhizosphere yang diukur dengan metodeBray-1 P. Hasil penelitian menunjukkan bahwa daun ke-2 adalah posisidaun yang sesuai sebagai contoh daun untuk analisis status P pada bibitjarak pagar (Jatropha curcas L.). Kadar P di rhizosphere lebih rendahdaripada kadar P di tanah (Bray-1P) yang jauh dari akar jarak pagar. Padadaun ke-2, keeratan hubungan yang ditunjukkan oleh koefisien regresi (R2)antara kadar Bray-1 P di rhizosphere dan kadar P daun jarak pagar (R2 =0.394) lebih tinggi daripada hubungan antara kadar Bray-1 P di tanah dankadar P daun (R2 = 0.371), sehingga untuk keperluan menggambarkanketersediaan P tanah atau untuk melihat hubungan P tanah tersedia dengankadar ataupun serapan P tanaman jarak pagar, akan lebih tepat bila contohtanah yang diambil berasal dari rhizosphere akar tanaman.Kata kunci: Jarak pagar (Jatropha curcas L.), posisi daun, status P, Ptanah tersediaABSTRACTDetermination of leaf sample position for analysis of Pstatus in physic nut (Jatropha curcas L.) seedlings andthe available P in the root zoneStatus of P in plants can be quantified by analyzing concentrationsof the nutrient in leaf as the leaf is the most active plant part. For this,information on appropriate leaf position as samples for analysis of P statusin the plants is needed. A research was conducted with aims to determinean appropriate leaf position of physic nut seedlings and to studydifferences between the concentrations of available P (Bray-1 P) in thebulk soil and the rhizosphere, along with their relationships with theconcentrations of leaf P. The experiment was carried out in a glasshouse ofIndonesian Spices and Other Industrial Crops Research Institute,Sukabumi, West Java, from September 2006 to July 2007. The experimentwas arranged in a completely randomized design with three replications.Each experimental unit consisted of 20 plants. The treatments were: (a) 1stleaf or a leaf located exactly below the shoot, (b) 2nd leaf or a leaf locatedbelow the 1st leaf, (c) 3rd leaf, and (d) 4th leaf. All the leaves were takenfrom the primary branch of the plants. Parameters measured were Pconcentrations in the leaf, P concentrations in the bulk soil and therhizosphere (Bray-1 P). The results showed that the 2nd leaf position wasthe appropriate leaf position to be taken as samples for the leaf analysis ofP status in physic nut (Jatropha curcas L.) seedlings. The concentrationsof Bray-1 P in the rhizosphere were lower than that in the bulk soil, whichis further away from the roots. The R2 values for the relationships betweenthe Bray-1 P concentrations in the rhizosphere and the the 2nd leaf Pconcentrations were higher than that between the Bray-1 P concentrationsin the bulk soil and the 2nd leaf P concentrations, hence, for the objectivesto show the soil P availability or to show the relationships between theavailable soil P and the concentrations or the P uptake by the physic nut, itwill be more accurate if the soil samples are taken from the rhizosphere.Key words: Physic nut (Jatropha curcas L.), leaf position, P status,available soil P