Show SI CAPTCHA below comment textarea

Thanks, I find the solution.
Si Captcha add captcha field after filter (comment_form_default_fields) in the comment form.

I have made change in comment.php file in theme folder.
comment_form();
replace this with

<?php
$comment_args = array(
 'comment_field'        => '',
'fields' => apply_filters( 'comment_form_default_fields', array(
		'author' => '<p class="comment-form-author">' . '<label for="author">' . __( 'Name' ) . ( $req ? ' <span class="required">*</span>' : '' ) . '</label> ' .
		            '<input id="author" name="author" type="text" value="' . esc_attr( $commenter['comment_author'] ) . '" size="30"' . $aria_req . ' /></p>',
		'email'  => '<p class="comment-form-email"><label for="email">' . __( 'Email' ) . ( $req ? ' <span class="required">*</span>' : '' ) . '</label> ' .
		            '<input id="email" name="email" type="text" value="' . esc_attr(  $commenter['comment_author_email'] ) . '" size="30"' . $aria_req . ' /></p>',
		'url'    => '<p class="comment-form-url"><label for="url">' . __( 'Website' ) . '</label>' .
		            '<input id="url" name="url" type="text" value="' . esc_attr( $commenter['comment_author_url'] ) . '" size="30" /></p>',
		'comment_field'        => '<p class="comment-form-comment"><label for="comment">' . _x( 'Comment', 'noun' ) . '</label><textarea id="comment" name="comment" cols="45" rows="8" aria-required="true"></textarea></p><br>',
		)),
	);
comment_form($comment_args); ?>