Exploitation of soil arbuscular mycorrhizal potential for AM-dependent mandarin orange plants by pre-cropping with mycotrophic crops

Abstract

Results of a nursery study on the effect of short season pre-cropping with differently mycotrophic herbaceous crops on growth of arbuscular mycorrhiza-dependent mandarin orange plants at an early stage after transplantation are presented. The study was carried out with eroded, low nutrient, acidic, brown forest soil of the North-Eastern Himalayan region of India. Mandarin orange seedling plants at 180 days after transplantation showed variation in shoot growth response to single season pre-cropping with seven different crops—maize, Paspalum millet, soybean, onion, tomato, mustard and ginger and two non-cropped fallow treatments—non-weeded and weeded fallows. Net growth benefit to the orange plants due to the different pre-crops and the non-weeded fallow treatment over the weeded fallow treatment plants showed highly significant positive correlation with mycorrhizal root mass of the orange plants as it varied due to the different pre-crop treatments. Net growth benefit due to the pre-crops and weeds varied between 0 and 50% depending upon the mycorrhizal root mass of the pre-crops and weeds, AMF spore number and infective inoculum density of the pre-cropped soils. These pre-crop variables individually and cumulatively contributed to the highly significant positive correlation between the AMF potential of the pre-cropped soils and growth of mandarin orange plants through their effect on mycorrhizal root mass development (i.e. extent of mycorrhization) of the mandarin orange plants. The results show that choice of a pre-crop from the available options practised by the farmers, grown even for a short season can substantially alter the inherent AMF potential of soils to significantly influence the performance of the mycorrhiza-dependent orange plant. The relationship between soil mycorrhizal potential left by a pre-crop and mycorrhizal benefit drawn by the succeeding AM responsive plant can be taken advantage of in the exploitation of native AMF potential of soils for growth and nutrition management of crops in low nutrient, low input–output systems of production.