Dr Sabina Asins has kindly alerted me to the marvellous The Manuscript@CSIC portal which presents the digitized collections of manuscripts in Hebrew, Arabic and Aljamiado held in the network of CSIC libraries: http://manuscripta.bibliotecas.csic.es/inicio
It includes Ibn Luyun's Kitāb ibdāʼ al-malāḥa wa-inhāʼ al-raŷāḥa fī uṣūl ṣināʽat al-filāḥa
preserved in the manuscript held by the Biblioteca de la Escuela de Estudios Árabes (C.S.I.C.) in Granada. It can be accessed herehttp://aleph.csic.es/imagenes/mad01/0006_PMSC/html/001349506.html#page/1/mode/2up
Thank you CSIC!