Gliricidia Intercropping Shade Trial Data
Legumes are known for their ability to add nitrogen and organic matter to the soil. In most cases, cereal crops including maize are intercropped with annual legumes. There are, however, nitrogen-fixing trees that may also be used. Maize is normally grown under full sun, but some shade may benefit the crop in hot, dry areas due to lower temperature. Positive or negative effects of growing crops with trees could be due to a combination of factors including light/shade, temperature, soil moisture, leaf litter/organic matter, and nitrogen fixation.
This trial was initiated in 2018-19, in southwest Florida (at ECHO Inc. in North Fort Myers), to study the effect of shade on maize intercropped with cowpea (Vigna unguiculata). Maize grown in alternating rows with cowpea is subjected to three treatments:
1) no shade (control)
2) shade from gliricidia trees spaced 6 m apart in a triangular pattern
3) shade from shade cloth that intercepts 30% of incoming light
The purpose of the third treatment is to be able to assess and learn about the effect of shade on the maize, without the addition of leaf litter and nitrogen from the gliricidia trees. The comparison is not perfect, as gliricidia is likely to provide intermittent shade (with portions of the field in shadow at varying times of the day) while shade cloth provides dispersed shade (constant shade over the entire plot)Treatments are replicated three times in a randomized complete block design.
The maize and cowpea were planted at the same time during in early June of 2019, at which time the gliricidia seedlings were approximately 1 m tall. We plan to keep this trial going for multiple years. In future years, the gliricidia trees will be pruned back to a height of 1 m at maize/cowpea planting time.
As part of the trial, an arduino-based light logger is placed in the middle of one of the gliricidia plots. Data from the light sensors are used to calculate percent shade under the gliricidia trees, just above the maize plants. Below are graphs showing data as it comes in every 20 minutues. With widely-spaced trees, shade is expected to be intermittent, especially before the tree canopy is fully developed. Shade is most likely to occur during the morning and afternoon hours when shadows are longest; the least amount of shade occurs when the sun is directly overhead. Negative values for percent shade usually happen during morning and afternoon hours; they can be caused by slight differences in the angle of the sensors and residue on the sensors (which need to be cleaned from time to time).