Seedbed Conditions and Prediction of Field Emergence of Soybean Seed

Abstract

It has been difficult to develop consistent relationships between lab measures of soybean [Glycine max (L.) Merr.] seed quality (germination and vigor) and field emergence. Twenty six field emergence experiments (two to four planting dates per year) were conducted over 10 yr to evaluate the effect of seed bed conditions and carryover vs. noncarryover seed on the relationship between standard germination (SG) or accelerated aging germination (AA) and field emergence. Seedbed conditions were characterized by the field emergence index (FEI = mean field emergence/mean SG × 100) calculated for each experiment. The ability of the lab tests to predict field emergence was evaluated by the prediction accuracy (proportion of the seedlots in each test with a specified quality level that had a field emergence above the minimum level). The FEI varied from 108 to 44 and the prediction accuracy varied from 0 to 100%. The prediction accuracy was high for SG and AA for ideal field conditions (FEI ≥ 100) and decreased as soil stress increased. The AA test had higher prediction accuracy than SG in moderate stress. Lowering the minimum acceptable field emergence from 80 to 60% improved the prediction accuracy for SG and AA, but only seedlots with AA ≥ 80% showed acceptable prediction accuracy over a wide range of seedbed conditions. Noncarryover seed had higher prediction accuracy than carryover seed for SG, but there was little difference for AA. High vigor seed (AA ≥ 80%) provided adequate performance in a wide range of seedbed conditions only when the minimum acceptable emergence was lowered to 60%. Research Question Seed quality (germination and vigor) is measured and reported to provide an indication of the expected emergence when the seed is planted in the field. Establishing consistent relationships between lab measures of seed quality and field emergence is difficult because emergence is influenced by seed quality and by the seedbed environment. Soil temperature, water and oxygen levels, microorganisms, and soil structure vary widely from field to field and help determine whether the seed will germinate and whether the seedling will emerge. Seedbed conditions must be included in any evaluation of the relationship between seed quality and field emergence. The objectives of this research were to evaluate the relationship between germination and vigor test results and seedling emergence as affected by (i) seedbed conditions, (ii) the percentage emergence required to produce adequate plant populations, and (iii) carryover and noncarryover seed. Literature Summary Correlation and regression analysis are used to evaluate the relationship between lab measures of seed quality and field emergence. Significant relationships for soybean seed have been found for standard germination (SG) and several vigor tests including accelerated aging germination (AA). However, the relationships were not consistent from experiment to experiment and could not predict potential field performance. Combining the results of several lab tests into a single vigor index or a multiple regression equation was no better than using the individual tests. Study Description Twenty-six field emergence experiments were conducted over 10 yr. Soybean seedlots that had either been harvested the previous fall or had been in warehouse or controlled environment storage for up to 30 mo (carryover) were planted in the field on two to four planting dates each year. Standard germination and AA (seed vigor) were measured just before the first planting date each year. The field emergence index (FEI = mean field emergence/mean SG × 100) was calculated for each experiment to characterize seedbed conditions. The performance of the seedlots was assessed by determining whether the emergence was equal to or above a minimum acceptable level. The prediction accuracy was computed for each field planting as the proportion of the seedlots having a defined lab quality level that had emergence above the minimum acceptable level. Applied Questions Is the predictive ability of lab quality tests affected by soil conditions? Results of the SG and AA tests accurately predicted field performance (prediction accuracy of 100%) only in ideal field conditions. The prediction accuracy of both tests decreased as stress in the seedbed increased and eventually reached zero in severe stress conditions. Was there any difference in predictive ability between standard germination and accelerated aging germination? In ideal field conditions, the prediction accuracy of both tests was 100%. As soil stress increased the predictive ability of SG decreased faster than AA. In moderate stress conditions, the AA test always had a higher predictive ability than SG. Was it possible to get acceptable prediction accuracy over the range in field conditions likely to be encountered by soybean producers? To get predictions accuracy's of 80% or greater (80% of the seedlots produced acceptable stands) across the field conditions likely to be encountered by soybean producers in Kentucky, it was necessary to select seedlots with an AA of 80% or greater and use a minimum emergence standard of 60%. Was there any difference between carryover and noncarryover seed? The prediction accuracy for noncarryover seedlots with SG of 80% or greater was higher than for carryover seedlots, but the prediction accuracy for seedlots with an AA of 80% or greater was the same for carryover and noncarryover lots.