Review of seed pelletizing strategies for arid land restoration

Arid lands face numerous restoration challenges due to infrequent and irregular precipitation which impacts plant germination, growth, and survival. Abundant seed predators, harsh surface conditions, and native seeds often poorly suited to mechanical distribution compound restoration challenges. Seed pellets (a.k.a. pods, seed balls, and seed bombs), an aggregation of clay, soil, water, and multiple seeds, have the potential to reduce some of the challenges. However, no formal guidelines based on an aggregated research review exist. Available publications, both peer-reviewed and any public domain, were reviewed. Of the 24 publications found (some describing multiple tests), seed pellets tested on rangelands had 9 negative effects, 10 neutral effects, and 8 positive effects. Greenhouse testing showed five negative effects, two neutral effects, and four positive effects. Forest systems had three neutral effects and two positive effects. Advantages in mechanical distribution were not well quantified and other effects were lumped together in germination and seedling establishment totals. The use of pelleted seed would benefit from a more mechanistic understanding of the interaction between the pellets and the systemic constraints. As long as the pellets themselves do not greatly reduce germination or establishment, they appear a potentially viable method for improving seed distribution and seeding efficiency, protecting seeds, and adding amendments. While the evidence is far from conclusive, seed pellets may also hold some advantages in increasing germination and establishment.