OrganicFarmer_AugSep2018_e

Fertilizer injection in an organic ranch.
All photos courtesy of Gerry Spinelli.
Table 1. Nitrogen balance and corresponding marketable yield obtained from seven organic strawberry ranches.
yield. Therefore, in organic strawberry
systems, it is paramount for growers to
maximize yields by optimizing nitrogen
management. However, there are a
wide variety of nitrogen management
practices in organic systems, differences
in the total quantity of nitrogen applied
throughout the season and differences
in the timing and method of applications.
In this article, we report and discuss
the nitrogen balance for organic
strawberry in seven commercial ranches
in different years, from 2014 to 2017.
The nitrogen sources considered are:
1) residual nitrogen from the previous
crop; 2) fertilizer applications; 3) nitrate
applied through irrigation water and 4)
mineralization of organic matter. Yields
and modeled nitrogen uptake are also reported. The nitrogen uptake was obtained
from CropManage, a web-based decision support tool for irrigation and nitrogen
management developed by the University of California Cooperative
Extension (UCCE).
Regulations
In recent years, a more restrictive regulatory
environment for groundwater nitrate contamination
has evolved, which requires some growers
to report the ratio of applied nitrogen fertilizer
to nitrogen crop uptake. It is likely that in the
future, more growers will need to monitor more
closely the nitrogen inputs to the crop in order
to manage nitrogen applications to match crop
uptake. However, it is challenging for growers to
adjust the quantities of nitrogen available to the
crop since some of the factors influencing nitrogen
availability in the soil are not under growers’
Continued on Page 20
August/September 2018
www.organicfarmermag.com
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