Annual Report of Progress
to the
MISSISSIPPI SOYBEAN PROMOTION BOARD
for 1998

Objectives

1. To explore the possibility of growing early maturity varieties in Mississippi
2. To find out the optimum planting time for early maturity varieties
3. To obtain phenological and physiological data for growing early maturity varieties
4. To estimate the yield potential of early maturity varieties

Introduction

In recent years, early soybean production system (ESPS) has been recommended in the South. The advantage of this ESPS system is to plant earlier maturity varieties at an earlier time so that the soybeans can be harvested earlier and avoid the drought s tress. This system has a particular advantage to those non-irrigated soybeans since early harvested crops usually require less irrigation or non-irrigation (at any "normal" year). Soybean farmers have more time for land preparation. Since early maturity soybeans (MG-IV) have been introduced to Mississippi, it has had a considerable degree of success. Now those early varieties have been planted to more than 25% of total varieties (Zhang, 1997). However, there is a potential problem because the harvest tim e for MG IV is in early September when many rice farmers will harvest their rice. Because of this conflicting practice, many rice farmers have given up growing MG IV soybeans. If the harvest date can be pushed even two to three weeks earlier, then they may resume interest in growing early soybean varieties. From previous experience, we know that to further push an earlier planting date will not increase early harvest. Planting MG IV earlier too early will result in earlier flowering and shorter plants and lower yield. 

To further explore the potential of the early maturity soybeans, we have tried to introduce some varieties with even earlier maturity (MG-III) from the North. The purpose of this study was to examine if it is feasible to grow those earlier varieties, and if they can produce acceptable yields and also get early harvest. If these MG-III varieties can be grown in MS, it may give soybean growers more choices of varieties, wider range of planting and harvesting times, more adaptability to soils, especially for those non-irrigated fields, without much yield loss. 

Materials and Methods

Sixteen MG III varieties were used in the experiment. Most of the varieties were introduced from Missouri, Tennessee, and Illinois. HBK 4600 (MG IV) and a Hutcheson (MG V) were also included as checks to compare with those early varieties in physiological characters, phenological development, final yields, and yield components. The varieties involved are listed in Table 1. Soybeans were planted at four different planting dates, starting from March 13 to May 12, with approximate 20 days interval (April 2 and April 23 for other two planting dates). The plots were four rows with 20-ft length and 20-in row-spacing. The seed rate was at eight seed per foot, which makes a population density nearly to 209,000 seeds per acre. The first three plantings were replicated plots with a randomized block design with four replications. There were only eight varieties planted in the first planting. The last plantin g was a single row plot due to shortage of the seeds. 

The soil was a mixed loam. Each planting was divided into irrigated and non-irrigated plots, except planting IV which contained all irrigated plots. The irrigation started in early May. Both dates and rainfall amount are provided in Table 2. 

The fields were cultivated twice to control weeds during growing season. All other practices followed the recommended procedures for produce the maximum yield in the area. 

Results and Discussion

Phenological development: 
The phenological events of maturity group III, IV and V soybeans are summarized in Fig. I. The figure indicates that soybeans planted early experienced a longer growing season and did not get harvested proportionally as might be expected. The ratio of de layed planting to delayed harvest was about 3:1, which means that if the planting time has been delayed for three days, the harvest date may only be delayed for one day. Different MGs also have different phenological responses. In this study, the differen ce of planting dates between first planting and the fourth planting of maturity group V soybean was more than 10 weeks; however, the difference of harvesting dates of these two plantings was only about three weeks. Meanwhile, for the same about two planti ngs of MG III, the difference of harvesting dates was about six weeks. 

The reasons for this phenological development phenomenon are mainly from two aspects. The first is temperature effect. The temperatures during early growing season are usually low. Plants grow slower under this circumstance. The second is photoperiod. Early planted soybeans grow under a long-day condition for a longer time, which promotes a longer vegetative growth and slows down the reproductive growth. 

Analysis of yield components and yields: 
Data of various yields and yield components (Table 3 to Table 10) showed that March planting was obviously too early for varieties of MG-III as well as MG-IV and MG-V. The early-planted soybeans grew under short photoperiod and resulted in an early flowering. Therefore, plants matured too early. The plant height was too short (Table 3), and the fertile nodes were too few to produce acceptable yield (Table 4). Soybeans of MG-III varieties planted in early April ha d higher yields compared with that planted in March (Table 10). However, compared MG-IV and V with the same planting date, the yields of MG III were still too low to be accepted. The average yield of MG-III varieties of late April planting was much closer to that of MG-IV and MG-V. Actually, the top variety, Eisenhower, had a yield higher than that of both of HBK 4600 (IV) and Hutcheson (V) (Table 10). Eight varieties in irrigated plots and six varieties in non-irrigated plots had a yield at 55 bu/A or higher (Table 10). Among other physiological characters, the data of some of the top performed varieties from MG III also showed compatible numbers (Table 3-9). 

1. Optimum day-length: From early May to later June, the day-length increases continually and reaches the peak on June 21. When MG III varieties were planted around late April and early May, after seed germination, the vegetative growth experienced increased day-length. This long day-length helped vegetative growth and delayed flowering time. Therefore, by flowering time, plants have enough vegetative reserves to be used for reproductive needs later. 
2. Indeterminate nature: Most of MG III varieties we used were indeterminate varieties. Therefore, even for plants flowered with a relatively shorter time (comparing with MG- IV and V), the vegetative growth continued. So, the final vegetative growth didn't reduce plants flowered early. Also due to the indeterminate nature, total main stem node number (Table 4) and total fertile node number (Table 6) of MG III varieties were no less than those of MG IV and MG V. 

Shattering problems: 
Shattering is one of the problems that growers may face when growing MG III soybeans in Mississippi. Early maturity soybeans usually have a shorter shattering life. That was basically true in this study However, there are still some differences among vari eties. Most varieties can hold seeds relatively well after maturity. It is noticed that MG III variety, Saline, had shattered earlier compared with other MG III varieties (Table 9). In the future, shattering characteristics may be a breeding goal for bree ders if the MG III become more popular in the South. 

Seed Quality: 
Seed quality of MG III varieties is one factor that we have examined. In our study, we found that the early harvested seed had poor quality in term of germination rate. Late harvested seeds (planting 3 and 4) had a better quality. That corresponded with pervious experiences. The detailed data is still under analysis. 

Weed problem for early varieties: 
March planting and early April plantings had weed problems more serious than that of late plantings. Plants were too short in early plantings, causing early exposure and more space for weed development after leaf senescence starting at R6 stage, especiall y for those plots in irrigated fields. The way to prevent this is to 1) reduce the plant spacing if planted early; and 2) choose varieties with taller stem and more vigor in vegetative growth. 

Summary

Based on the results in 1998, several suggestions may be proposed for growing MG III soybeans in Mississippi. First is to select the varieties that possess good potential of physiological characters and yield potential. The second is to plant soybeans not too earlier. The best planting window may be between mid-April and mid-May. To avoid the weed problem in early plantings, soybeans may be better plant with a narrower row-spacing, such as 20-inch to 15-inch or narrower (such ad drill planting). Maturity Group III soybeans may be especially good for those non-irrigated fields. 

Publications 

An abstract has been prepared and submitted to World Soybean Research Conference VI at Chicago, USA. Aug.1999 (see summary abstract page).

Soybeans in Mississippi Mississippi Agricultural and Forestry Experiment Station  Mississippi State University Extension Service Division of Agriculture, Forestry and Veterinary Medicine

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