Sunn Hemp (Crotalaria juncea L.) Intercrop and Mulch Reduces Wind Stress and Increases Growth and Development of Papaya (Carica papaya L.)

In some areas, including south Florida, papaya is subject to stress from high wind speeds during crop establishment.  The objectives of this study were to test the effects of a sunn hemp intercrop and mulching system on reducing potential wind stress and increasing the growth and yield of papaya. Sunn hemp was planted as an intercrop between rows of ‘Red Lady’ papaya plants.  After papaya establishment, the sunn hemp intercrop was mown and used as mulch by retaining all the aboveground biomass on the soil surface in the papaya bed. There were three treatments: 1) control (no sunn hemp) and two sunn hemp treatments; 2) early mown (sunn hemp mown 10 weeks after field planting papaya); and 3) late mown (sunn hemp mown 16 weeks after papaya planting).  Weeding was done by hand and the time taken to weed each treatment was recorded.  Measurements in the papaya crop included leaf gas exchange, stem length and diameter, first flowering date, and yield.  Prior to mowing, wind speeds at the top of the papaya canopy were reduced in the sunn hemp treatments as compared to the control treatment. The degree of reduction varied by external wind speed and direction.  Also, prior to mowing, papaya plant growth was reduced by approximately 25% in the late mown treatment compared to the other treatments, probably as a result of sunn hemp shading the papaya plants.  However, by 1 month after mulching, the stem diameter in the early mown treatment exceeded that of the control by approximately 30%.  For both sunn hemp treatments, mulching increased net CO₂ assimilation and growth of papaya, and hastened the beginning of harvest. Weeding time was reduced by about 75% in both sunn hemp treatments compared to the control.  The data indicate that use of sunn hemp as an intercrop and subsequent mulch for papaya can reduce potential wind stress and increase papaya crop vigor and growth and hasten harvest time due to enhanced physiological performance leading to more rapid reproductive development.