[devote]

$data = array();
$data["day"]=1;
$data["mounth"]="january";
$data["year"]=2013;
$data["data"]=massiv;
echo json_encode($data);

или

$data = array(
    'day' => 1,
    'mounth' => "january",
    'year' => 2013,
    'data' => massiv
);
echo json_encode($data);

или

echo json_encode(array(
    'day' => 1,
    'mounth' => "january",
    'year' => 2013,
    'data' => massiv
));