Abstract
An indicator needed for estimating the presence of response of cocoa (Theobroma cacao) trees to nitrogen (N) fertilizer has been well understood, however there is still little progress on the work on identification of organic N fraction which regulates the response of cocoa to N fertilizer. The objective of this study is to identify a fraction of soil organic N which is very closely related with degree of cocoa response to N fertilizer. Hydrolyses were performed on soil samples derived from 23 sites of cocoa plantations distributed both in Banyuwangi district (12 sites) and in Jember district (11 sites). Analysis of organic N fractions consisted of total hydrolysable N, ammonium N, amino sugar N, amino acid N and combinations of those fractions. To investigate the level of cocoa plants response to N fertilizer, seedlings of cocoa were planted in plastic pots treated with and without urea as source of N. Degree of response of cocoa plants to N fertilizer was measured based on growth parameters, such as plant height, leaf number, stem girth, fresh weight of stem, leaf and shoot; and dry weight of stem, leaf and shoot. Results of this study showed that biggest response of cocoa was shown by dry weight of leaf at the level of 29,22% (in the range of -17,43% – 95,98%), whereas the smallest response was shown by stem dry weight at the level of -1,04 (in the range of -26,16 – 47,54). From those of organic N fractions analyzed, only N ammonium did not show any significant correlations with all the growth parameters observed. Leaf dry weight was the most closely related parameter with nearly all organic N fractions followed by shoot dry weight and stem girth. The soil organic N fraction which had very significant relation with cocoa plant response was total hydrolysable N. Using the method of Cate-Nelson, it was revealed that cocoa gardens contain total hydrolysable N less than 1273 mg/kg were classified as responsive to N fertilizer.Key words: plant response, Theobroma cacao, soil organic nitrogen, N fertilizer, soil testing, fertilization, soil variability, soil hydrolysis
Highlights
The objective of this study is to identify a fraction of soil organic N which is very closely related with degree of cocoa response to N fertilizer
Results of this study showed that biggest response of cocoa was shown by dry weight of leaf at the level of 29,22% (in the range of -17,43% – 95,98%), whereas the smallest response was shown by stem dry weight at the level of -1,04 (in the range of -26,16 – 47,54)
Pengaruh pemupukan nitrogen dan fosfat terhadap produksi jagung pada tanah Hydric Dystrandept Jawa Barat dan Typic Paleudult Lampung
Summary
An indicator needed for estimating the presence of response of cocoa (Theobroma cacao) trees to nitrogen (N) fertilizer has been well understood, there is still little progress on the work on identification of organic N fraction which regulates the response of cocoa to N fertilizer. Results of this study showed that biggest response of cocoa was shown by dry weight of leaf at the level of 29,22% (in the range of -17,43% – 95,98%), whereas the smallest response was shown by stem dry weight at the level of -1,04 (in the range of -26,16 – 47,54) From those of organic N fractions analyzed, only N ammonium did not show any significant correlations with all the growth parameters observed. Dengan demikian diperlukan suatu indikator yang mampu menunjukkan bahwa suatu lahan akan respons atau tidak terhadap pemupukan nitrogen sebagai suatu dasar rekomendasi dalam pemberian pupuk. Upaya untuk memproduksi tanaman berdasarkan rekomendasi pemupukan memiliki manfaat jangka panjang, tetapi pemupukan yang kurang atau berlebih dapat terjadi dalam suatu musim tanam karena ketersediaan N tanah tidak dipertimbangkan berhubung dalam analisis N tanah sering ditujukan pada kandungan N total tanah. Penelitian ini bertujuan untuk mengidentifikasi senyawa organik N tanah tertentu yang dapat digunakan sebagai indikator kemampuan tanaman kakao pada suatu tanah tertentu dalam merespons pemupukan nitrogen
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