Title: Optimum planting configuration for alfalfa production with ridge-furrow rainwater harvesting in a semiarid region of China

Abstract

Soil desiccation is a major challenge faced by subsistence farmers growing alfalfa (Medicago sativa L) in consecutive cultivation in semiarid regions. We hypothesized that alfalfa fodder yield would increase with the length of growing season, growing degree-days, and rainfall. A field experiment was conducted on alfalfa production from 2012 to 2016 to 1) determine the response of fodder yield to rainfall, the length of growing season, and accumulated growing degree day (AGDD) in different growing-cutting stage (GCS)s; 2) obtain the suitable mulching material and the optimum ridge width for ridges with manually compacted soil (MCS), mulched with bio-degradable film (BF), and plastic film (PF). There were 10 treatments (3 ridge widths × 3 ridge-mulching materials + flat planting (FP) as control) with three replications laid in a randomized block design. The ratio of the first GCS to the second GCS in fodder yield ranged from 1.10 to 4.55, which was similar to the ratio of the first GCS to the third GCS in fodder yield ranged from 1.14 to 4.59, although rainfall, the length of growing season, and AGDD were different during the two or three GCSs. The highest fodder yield was obtained from the first GCS in one year and reached the highest level in the second growing year, and maintained a similar level in the subsequent years, although rainfall, the length of growing season, and AGDD varied during the five year periods. Fodder yield was affected by both the rainfall in the GCS and the available soil moisture prior to the GCS. Compared to FP, the increase of evapotranspiration for MCS, BF, and PF was 11, 61, and 63 mm, respectively. Fodder yield for BF and PF increased by 28% and 33%, respectively. Fodder yield for MCS maintained the same level as that for FP. Evapotranspiration increased and fodder yield decreased as ridge width increased. The optimum ridge width for MCS, BF, and PF was 29, 39, and 37 cm, respectively, across five years. Future study should focus on alfalfa-crop rotation to mitigate soil desiccation after alfalfa consecutively production.