Biodegradable mulch of recycled paper reduces water consumption and crop coefficient of pak choi

•Local crop coefficient of pak choi was determined in two cultivation systems.•Biodegradable mulch of recycled paper reduced water consumption by 33–41%.•The crop coefficient curve was influenced by the biodegradable mulch of recycled paper.•Crop coefficient should be corrected for the regional climatic condition.•Crop coefficient can be predicted using a vegetation index.•Water requirement is between 128 and 142 mm for unmulched pak choi and between 83 and 85 mm for mulched pak choi. Unlike plastic mulch, which has environmental concern, recycled paper as mulch has the sustainable potential to be used in the production of vegetables and can be adopted in the cultivation of pak choi (Brassica rapa ssp. pekinensis). However, there is no information on water savings and values of crop coefficient, which are used in irrigation management, generating a demand for research. The crop coefficients (Kc) of mulched (recycled paper) and unmulched pak choi were modeled as a function of cumulative growing degree days (CGDD) over two successive cultivation seasons, winter and spring. The study was conducted at the Lysimetric Station of the Federal University of Viçosa, in Viçosa, MG, Brazil. Reference evapotranspiration (ETo), required to calculate Kc, was obtained in situ by means of lysimeters cultivated with Bahia grass (Paspalum notatum). The models explained a large part of the data variability, with R2 from 0.45 to 0.75. Recycled paper significantly reduced water consumption mainly at the initial stage, also reducing Kc values. Kc values ranged from 0.36 to 1.58 for mulched pak choi and from 0.75 to 1.60 for unmulched one. The evaporation coefficient (Ke) of the mulch remained constant throughout the cycle, with a mean value of 0.32. The Normalized Difference Vegetation Index (NDVI) adequately fitted to pak choi phenology. The Kc can be estimated based on the NDVI for mulched and unmulched pak choi. Mulching did not improve pak choi yield, but significantly increased its water use efficiency. In the winter, pak choi heads became more compact. The models found in this study are a useful tool for producers to estimate the water requirements of the crop. These results represent an important contribution to improving the use of irrigation water in pak choi cultivation.