Almond and peanut hulls were clearly detrimental to the roots of both citrange and avocado roots and to the shoot growth of avocado. Discussion Citrus and avocado are well suited to benefit from mulches. They have very shallow root systems, with the far majority of their roots located in the top 1 to 2 feet of soil. Among the mulches examined, the structure and chemical composition of yard waste most closely resembles a forest litter layer similar to that in which citrus and avocado evolved. The authors believe that citrus responded better with higher nitrogen and lower carbon mulches than did avocado because citrus responds to nitrogen deficiencies far more rapidly than does avocado.
Animal manures are among the most common amendments applied to citrus and avocado orchards.
The authors noted that root damage after application of high ammonia-releasing manures is common, especially to young trees. Young trees are also more sensitive to Phytophthora infection. They also caution against extrapolating the results of these greenhouse experiments to effects of mulching in the field. The successful growth of the three microbial biocontrol agents on several mulching materials was promising. Strains of the three species tested, the common soil bacterium, Pseudomonas fluorescens and the ubiquitous soil fungi, Gliocladium virens and Trichoderma harzianum , have showed potential for suppressing Phytophthora root rots of avocado and citrus in previous greehnouse experiments.