Nutrient Management Research Database

Seedless table grape cultivars, particularly ‘Thompson Seedless’, represent about 25% of the total area planted and is one of the most important export crops in Chile. This grape is produced in different regions, the Limari Valley-Coquimbo, in the IV region, one of the most important producing regions in the world. Due to low organic matter content in soil and a rainfall regime (approximately 100 mm/year), application of different organic matter (OM) sources, especially goat manure, is a common practice, intended to decrease plant decay and stimulate root development. The main objective of this research was to evaluate the effect of the application of grape pomace compost and humic acids as organic amendments on some soil quality indicators and agronomic variables in table grape, using a randomized experiment with 20 treatments evaluating two organic sources in four C rates (compost from grape pomace, 500, 1000 and 2000 kg C/ha; liquid humic acids, 100, 200 and 400 kg C/ha), in presence and absence of chemical fertilization and commercial microbial inoculants were evaluated. Nutrient availability, microbial populations and enzymatic activities were defined as measured variables. The use of organic matter as source of organic carbon alone or in combination with microbial inoculants will be a proper management for modern horticulture systems, is an integrated form to produce environmentally safe and economically viable.

• This experiment was performed on potted 'Thompson Seedless' variety table grapes.
• The effects of adding either composted grape pomace, goat, and horse manure or humic acid at a range of application rates were monitored.
• Soil characteristics observed included soil N and P levels, humic and fulvic acids (types of soil organic matter), pH, and EC.
• Also monitored were a handful of indicators of the soil microbial community, including the number of microbes and enzyme activity.
• As well, agronomic properties such as root dry matter, root density, and trunk diameter were measured. 

Compost application stimulated strong root development, increased root density, soil P and N levels, and phosphotase enzyme activity. Phosphotase is involved in making P plant available.

Compost introduces highly active microbes to the soil.

Manure P and N was more efficiently used than when liquid humus was added.

Since plant N absorption is highest between bloom and veraison, applications are best timed in the late spring.

Plants with a well developed root system will be more resilient to changes in nutrient and water supply, ensuring better yields and higher quality grapes.