Improving planting potential of lunar soil by adjusting grain size distribution

objectives Lunar soil is generated by the fine rock debris under physical weathering, the low aeration porosity and lack of organic matter make it unsuitable for planting. Improving the physical properties of lunar soil would provide a crucial tool to realize the In-Situ Resource Utilization (ISRU) of lunar soil for the space agriculture race.

Methods Based on the composition data of lunar soil samples retrieved from the lunar probe Chang’e-5, basalt was used to prepare simulated lunar soil (M0). Referring the particle size distribution data of lunar soil samples from Chang’e-5 and Apollo, soil groups, M0, M1, M2 and M3 were prepared by adding 0, 10%, 20% and 30% (wt) of basalt particles (1000−500 μm in size). N, P, and K nutrients were added into the simulated soils to carry out lettuce planting and laboratory leaching experiments.

Results With the increased addition of large size particles (M0, M1, M2, and M3), the bulk density of lunar soil decreased from 1.85 to 1.80 g/cm³, aerated porosity at field moisture capacity increased from 7.62% to 11.68%. With the increase of large particle proportion in the simulated soils, the NH₄⁺, total N and total P in the leachate decreased first and then increased, in other words, the nutrient holding capacity increased first and then decreased. The lowest NH₄⁺ andtotal N were determined in the leachate of M2, which were 58.10% and 21.67% lower than those in M0. In addition, the lettuce grew best in M2, the dry weight of above- and under-ground parts was 97.60% and 39.20% higher than those of M0, respectively.

Conclusions Adding large-size particles to simulated lunar soil can improve its physical structure, increase aeration porosity, reduce bulk density, thus improve its fertilizer retention capacity and planting potential. The primary addion ratio of large particals is 20% for the in-situ use of lunar soil.