6.1. Kesimpulan
Hasil percobaan di laboratorium menunjukkan bahwa pola dan laju pelepasan atau mineralisasi N dalam tanah tergenang sangat tergantung pada tingkat dekomposisi bahan organik (jerami segar atau kompos). Selama masa inkubasi tanah-bahan organik, nitrogen yang dilepaskan dalam tanah tergenang yang diberi potongan-potongan jerami se gar jauh lebih tinggi dibandingkan dengan yang diberi kompos jerami. Pemberian urea yang dikombinasikan dengan kompos mampu meningkatkan ketersediaan N dalam tanah serta mengurangi potensi imobilisasi N dalam tanah. Dengan kata lain, untuk jangka pendek jerami segar merupakan sumber N tanaman yang lebih baik dibandingkan dengan kompos. Selanjutnya pemberian potongan-potongan jerami segar (N ~ 0,9%) dengan takaran yang setara dengan 92 kg N ha-1 atau setara dengan 8,5 ton BK jerami per hektar merupakan sumber N yang baik bagi tanaman padi dan memberikan pengaruh yang sama baiknya dengan urea (dengan takaran N yang sama) terhadap serapan N, jumlah anakan, dan bobot kering tanaman padi. Selain itu, pemberian potongan-potongan jerami padi ke dalam tanah dengan kondisi tergenang dapat meningkatkan aktivitas enzim nitrogenase dari bakteri penambat N2, yang selanjutnya menjadi sumber N yang dapat digunakan oleh tanaman padi
pada stadia pertumbuhan generatif (the later stages of growth). Dengan demikian, pemberian jerami padi ke dalam tanah sawah dapat menjadi salah satu cara pengelolaan suplai N dalam budidaya padi sawah. Pemberian jerami juga dapat meningkatkan efisiensi pemanfaatan N pupuk oleh tanaman padi dan menurunkan emisi gas N2O.
6.2. Saran
Potongan-potongan jerami padi sebaiknya diberikan tanpa dikomposkan lebih dulu dan diberikan ke dalam tanah satu hari sebelum tanah digenangi. Selanjutnya jerami padi tersebut diinkubasi selama tiga minggu dalam kondisi tergenang sebelum penanaman bibit padi. Dengan cara ini diharapkan N-NO3-
akan diimobilisasi oleh jasad renik tanah, dan selanjutnya dilepaskan kembali ke dalam tanah saat lahan disawahkan sehingga tersedia bagi tanaman padi.
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Lampiran 1. Cara Penghitungan Serapan N dan N dari Bahan Organik dan Urea
Perlakuan :
A. Kontrol, 0 N (tanpa bahan organik dan urea)
50 mg 15N-ZA
B. Bahan organik tidak bertanda (Jo, J4, atau J8)
50 mg 15N-ZA
C. Urea tidak bertanda (U)
50 mg 15N-ZA
D. Bahan Organik dan Urea tidak bertanda (JoU, J4U, atau
J8U)
50 mg 15N-ZA
Perlakuan %15N a.e.* %15N tnm yang berasal dari ZA **
Kontrol 1,094 (1,094/9,633) x 100% = 11,357
Bahan Organik 0,614 (0,614/9,633) x 100% = 6,374
Urea 0,862 (0,862/9,633) x 100% = 8,948
Bahan Organik + Urea 0,679 (0,679/9,633) x 100% = 7,049
* Hasil analisis contoh tanaman dari percobaan pot
%15N a.e. dalam pupuk ZA yang diberikan ke dalam tanah = (10-0,367)% = 9,633%
** %15N dalam tanaman yang berasal dari pupuk ZA = (%15N a.e. dalam contoh tanaman / %15N a.e. dalam pupuk ZA) x 100%
Nitrogen Tersedia (A-value) Berdasarkan Me tode Pengenceran Isotop N oleh Tanaman :
A. Kontrol (tanpa Bahan Organik dan Urea) :
%N yang berasal dari pupuk ZA %N yang berasal dari tanah =
Takaran N dari pupuk ZA yang diberikan Atanah
(Sumber N hanya berasal dari pupuk ZA dan tanah)
11,357 100 – 11,357
= Atanah = 390,257 mg N setara
50 Atanah dengan pupuk ZA
B. Bahan Organik:
6,374 100 – 6,374 Atanah+bhn organik = 734,44
= Abhn organik = 734,44 – 390,257
50 Atanah+bhn organik = 344,18 mg N setara
dengan pupuk ZA C. Urea:
8,945 100 – 8,945 Atanah+urea = 508,78
= Aurea = 508,78 – 390,257
50 Atanah+urea = 118,53 mg N setara dengan
pupuk ZA
D. Bahan Organik dan Urea:
7,049 100 – 7,049 Atanah+bo+urea = 659,32
= Abo+urea = 659,32 – 390,257
50 Atanah+bo+urea = 269,06 mg N setara dengan
pupuk ZA Persentase N dalam tanaman yang berasal dari:
1. N-tanah :
%Ntanah %15N %Ntanah = (11,357 / 50) x 390,257
= = 88,643%
Atanah 50
2. N-bahan organik:
%Nbahan organik %15N %Nbahan organik = (6,374 / 50) x 344,18
= = 43,88%
Tabel Lampiran 2. Komposisi Kimia dari Sereal dan Jerami Padi (www.fiberfutures.org)
Sifat Kimia Sereal Jerami Padi Kayu Keras
(Hardwood) Selulosa (%) 45 – 55 43 – 49 57 Hemiselulosa (%) 26 – 32 23 – 28 23 Lignin (%) 16 – 21 12 – 16 25 Abu (%) 2 – 9 15 – 20 1 Silika (%) 2 – 8 9 – 14 0,5
Tabel Lampiran 3. Sidik Ragam pH Tanah Akibat Pemberian Jerami Padi, Kompos, Urea dan Kombinasinya pada Inkubasi Tanah di Laboratorium Sumber Keragaman Derajat Bebas (Db) Jumlah Kuadrat Kuadrat Tengah F-hitung P Hari ke - 1 Perlakuan 6 0,59039 0,0984 10,53 0 ** Galat 14 0,13087 0,00935 Total 20 0,72126 Hari ke -7 Perlakuan 6 0,59039 0,0984 10,53 0 ** Galat 14 0,13087 0,00935 Total 20 0,72126 Hari ke -14 Perlakuan 6 1,39538 0,23256 38,04 0 ** Galat 14 0,08560 0,00611 Total 20 1,48098 Hari ke -21 Perlakuan 7 1,1387 0,1627 15,25 0 ** Galat 16 0,1707 0,0107 Total 23 1,3094 Hari ke -47 Perlakuan 7 0,90646 0,12949 37,26 0 ** Galat 16 0,05560 0,00347 Total 23 0,96206
Lanjutan Tabel Lampiran 3 Sumber Keragaman Derajat Bebas (Db) Jumlah Kuadrat Kuadrat Tengah F-hitung P Hari ke -70 Perlakuan 7 1,11113 0,15873 30,92 0 ** Galat 16 0,08213 0,00513 Total 23 1,19326 Hari ke -96 Perlakuan 7 0,5101 0,0729 0,75 0,636 Galat 16 1,5581 0,0974 Total 23 2,0682 Hari ke-120 Perlakuan 7 0,8774 0,1253 4,03 0,01 * Galat 16 0,4979 0,0311 Total 23 1,3753
Tabel Lampiran 4. Sidik Ragam Konsentrasi N-NH4+ Tanah (mg kg-1) Akibat
Pemberian Jerami Padi, Kompos, Urea dan Kombinasinya pada Setiap Stadia Pertumbuhan Tanaman Padi
Sumber Keragaman Derajat Bebas (Db) Jumlah Kuadrat Kuadrat Tengah F-hitung P Pindah Tanam Perlakuan 7 409,1 58,4 1,44 0,256 Galat 16 648,3 40,5 Total 23 1057,4 Pembentukan Anakan Pe rlakuan 7 674,8 96,4 1,27 0,326 Galat 16 1217,4 76,1 Total 23 1892,2
Awal Pembentukan Malai
Perlakuan 7 24,27 3,47 1,1 0,406 Galat 16 50,20 3,14
Total 23 74,47
Pengisian Bulir Padi
Perlakuan 7 64,17 9,17 6,04 0,001 ** Galat 16 24,29 1,52 Total 23 88,46 Panen Perlakuan 7 8,35 1,19 0,67 0,691 Galat 16 28,31 1,77 Total 23 36,66
Tabel Lampiran 5. Sidik Ragam Jumlah Anakan per P ot Akibat Pemberian Jerami Padi, Kompos, Urea dan Kombinasinya pada Setiap Stadia Pertumbuhan Tanaman Padi Sumber Keragaman Derajat Bebas (Db) Jumlah Kuadrat Kuadrat Tengah F-hitung P Pembentukan Anakan Perlakuan 7 10 1,43 0,34 0,926 Galat 16 68 4,25 Total 23 78
Awal Pembentukan Malai
Perlakuan 7 294,7 42,1 1,66 0,191 Galat
16 406,7 25,4 Total 23 701,4
Pengisian Bulir Padi
Perlakuan 7 459,6 65,7 6,25 0,001 ** Galat 16 168 10,5
Tabel Lampiran 6. Sidik Ragam Bobot Kering Tanaman Padi (g per pot) Akibat Pemberian Jerami Padi, Kompos, Urea dan Kombinasinya pa da Setiap Stadia Pertumbuhan Tanaman Padi Sumber Keragaman Derajat Bebas (Db) Jumlah Kuadrat Kuadrat Tengah F-hitung P Pembentukan Anakan Perlakuan 7 3,234 0,462 0,77 0,62 Galat 16 9,595 0,6 Total 23 12,829
Awal Pembentukan Malai
Perlakuan 7 49,46 7,07 1,07 0,428 Galat
16 106,04 6,63 Total 23 155,5
Pengisian Bulir Padi
Perlakuan 7 2579,9 368,6 17,69 0 ** Galat 16 333,3 20,8 Total 23 2913,2 Saat Panen Perlakuan 7 163,2 23,3 0,76 0,626 Galat 16 489,5 30,6 Total 23 652,7
Tabel Lampiran 7. Sidik Ragam Serapan 15N (mg per pot) Tanaman Padi Akibat Pemberian Jerami Padi, Kompos, Urea dan Kombinasinya pada Setiap Stadia Pertumbuhan Tanaman Padi Sumber Keragaman Derajat Bebas (Db) Jumlah Kuadrat Kuadrat Tengah F-hitung P Pembentukan Anakan Perlakuan 7 32,63 4,66 1,16 0,377 Galat 16 64,23 4,01 Total 23 96,86
Awal Pembentukan Malai
Perlakuan 7 214,9 30,7 9,78 0 ** Galat
16 50,2 3,14 Total 23 265,1
Pengisian Bulir Padi
Perlakuan 7 13882308 1983187 7,8 0 ** Galat 16 4067753 254235 Total 23 17950061 Panen Perlakuan 7 13216 1888 18,78 0 ** Galat 16 1608 101 Total 23 14824
Tabel Lampiran 8. Sidik Ragam Serapan N yang Berasal dari Tanah (mg per pot) Akibat Pemberian Jerami Padi, Kompos, Urea dan Kombinasinya pada Setiap Stadia Pertumbuhan Tanaman Padi Sumber Keragaman Derajat Bebas (Db) Jumlah Kuadrat Kuadrat Tengah F-hitung P Pembentukan Anakan Perlakuan 7 1826 261 1,23 0,342 Galat 16 3388 212 Total 23 5214
Awal Pembentukan Malai
Perlakuan 7 22518 3217 11,14 0 ** Galat
16 4621 289 Total 23 27139
Pengisian Bulir Padi
Perlakuan 7 430170285 61452898 6,04 0,001 ** Galat 16 162707270 10169204 Total 23 592877555 Panen Perlakuan 7 73398 10485 16,46 0 ** Galat 16 10194 637 Total 23 83592
Tabel Lampiran 9. Sidik Ragam Serapan N yang Berasal dari Pupuk (mg per pot) Akibat Pemberian Jerami Padi, Kompos, Urea dan Kombi-nasinya pada Setiap Stadia Pertumbuhan Tanaman Padi * Sumber Keragaman Derajat Bebas (Db) Jumlah Kuadrat Kuadrat Tengah F-hitung P Pembentukan Anakan Perlakuan 6 1412 235 2,05 0,125 Galat 14 1605 115 Total 20 3017
Awal Pembentukan Malai
Perlakuan 6 22635 3772 5,89 0,003 ** Galat
14 8968 641 Total 20 31603
Pengisian Bulir Padi
Perlakuan 6 77702 12950 8 0,001 ** Galat 14 22670 1619 Total 20 100372 Panen Perlakuan 6 36099 6017 1,65 0,207 Galat 14 51144 3653 Total 20 87243
Tabel Lampiran 10. Sidik Ragam Efisiensi Penggunaan N Pupuk (%) oleh Tanaman Padi Akibat Pemberian Jerami Padi, Kompos, Urea dan Kombinasinya pada Setiap Stadia Pertumbuhan Tanaman Padi Sumber Keragaman Derajat Bebas (Db) Jumlah Kuadrat Kuadrat Tengah F-hitung P Pembentukan Anakan Perlakuan 6 66,74 11,12 2,05 0,126 Galat 14 75,88 5,42