Darbie M. Granberry

Heat units to predict tomato harvest in the southeast USA

Abstract Planting and first harvest dates of tomato ( Lycopersicon esculentum Mill.) from 2 seasons in 3 years at eight locations in Georgia, North Carolina and South Carolina formed 38 environments which were used to determine the most reliable method to predict fast harvest date of tomato based on daily maximum and minimum air temperature. Eleven methods of calculating heat units were chosen for comparison based on their performance as described in the literature. The most reliable method was defined as the one with the smallest coefficient of variation (CV). CVs were calculated for each method over both seasons and locations, for each season over all locations, each location over all seasons, and for each season at each location. All heat unit summation methods had smaller coefficients of variation (CV) than the standard method of counting days from planting to first harvest. Heat unit summation methods improved harvest date prediction accuracy compared with the counting day method for tomatoes in the South Atlantic Coast (SAC) region. Prediction using location/season specific models were less variable than the models over all seasons and locations. Incorporating daylength improved model prediction accuracy when applied over all locations and seasons, all locations by season, and all seasons by location. Based on the results of this study, the heat unit summation technique recommended for this region (where the location and season specific models are not available) is the reduced ceiling method multiplied by daylength.

Heat units, solar radiation and daylength as pepper harvest predictors

Abstract Daily maximum and minimum air temperature, total solar radiation and daylength data from seven locations during three seasons of 3 years were used to compare 52 heat unit accumulation models with counting days as a harvest prediction method for pepper. The best model was defined as the one with the least variation, i.e. smallest coefficient of variation (CV). CVs were calculated for each method over all seasons and locations, for each method over all locations for each season, and for each method in each season at each location. In all cases heat unit accumulation methods were better than counting days. The location and season specific model was the most accurate, but the analysis over all seasons and locations did result in smaller CVs than counting days, so improved harvest prediction can be achieved by using regionally developed models.

Influence of Cover Crops and Inorganic Nitrogen Fertilization on Tomato and Snap Bean Production and Soil Nitrate Distribution

ABSTRACT Commercial vegetable production depends almost solely on inorganic fertilizers. In an era of environmental sensitivity, enrichment of soils with green manures and cover crops may reduce the dependence on these fertilizers while maintaining and enhancing crop yields. The objectives of this research were to determine (1) if supplemental nitrogen (N) at 60 or 120 kg · ha−1 following winter cover crops of wheat (Triticum aestivum L.) or crimson clover (Trifolium incarnatum L.) affect yield of tomato (Lycopersicon esculentum Mill.) and snap bean (Phaseolus vulgaris L.) grown in rotation; and (2) the distribution and retention of soil nitrates in the soil profile as affected by N fertilization and cover cropping. ‘Mountain Pride’ fresh market tomato and ‘Strike’ snap bean were grown in rotation for four years. Clover and wheat cover crops increased total marketable yield of ‘Mountain Pride’ tomato in one out of four years. Total marketable tomato yield increased as fertilizer N increased to 60 kg · ha−1 in two out of four years and with 120 kg · ha−1 in one out of four years. N did not interact with cover crops to affect yield. ‘Strike’ snap bean marketable yield summed over all years was 60% lower in clover plots compared with fallow. Total marketable snap bean yield increased with 60 kg N · ha−1 in one out of three years but was unresponsive to N in two out of three years. Soil nitrates to 1.2 m depth were higher after clover and wheat than after fallow. Nitrate level was highest in soil with clover and 120 kg N · ha−1. In all cover crop or fallow plots, as fertilizer N application levels increased, the soil nitrates also increased. Cover crops or fertilizer N application did not increase the retention of residual nitrates in the 1.2 m soil profile depth after four years of cropping.