Alfalfa Yield Response to Additional Potash in the Tri River Area December 2000

A. Wayne Cooley (deceased) Area Extension Agent Tri River Area CSU Extension Montrose, Colorado

Dr. Jessica Davis Associate Professor CSU Extension Ft. Collins, Colorado

Cooperators
Grett Farms Olathe, Colorado	Delta Potato Growers Delta, Colorado	Potash and Phosphate Institute

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TABLE OF CONTENTS

Introduction

Objective

Materials and Methods

Results and Discussion

Table I: Alfalfa Potash Yield Results

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Introduction

Colorado State University Extension recommendations for potassium are zero if the soil test analysis results exceed 120 ppm available potassium in the soil. There have been comments made by producers and dealers that added potash provided greater yields of alfalfa even though a soil test analysis showed that no additional potassium was needed. However, there was no actual yield data to substantiate these observations.

The data to support the CSU Extension fertilizer recommendations has been primarily generated on the front range and eastern Colorado. There have been several field tests in the Tri River Area since 1996 to validate these recommendations. Nitrogen requirements for corn, potash requirements on dry beans, and nitrogen and phosphorus requirements on irrigated grass hay and irrigated mountain meadows have shown that CSU Extension recommendations, based on soil test analysis, are valid for the Tri River Area.

Objective

Conduct commercial size replicated field tests to determine if additional potash would significantly increase alfalfa yields when soil test analysis shows no additional potassium is needed based on CSU Extension recommendations.

Materials and Methods

1999 Test: Commercial size test plots were established October 15, 1998. The plots were 32 feet wide by 1200 feet long. The treatments included potash at 0, 66, 133, and 300 lbs/A and each treatment was replicated 3 times. The soil test analysis results showed over 300 ppm available potassium and since CSU Extension does not recommend any additional potassium above 120 ppm, this location should not require additional potash to maximize yields.

Three cuttings were harvested as green chop on June 8, July 20, and September 10, 1999. Each plot was harvested separately and the trucks were weighed utilizing commercial weigh pads.

2000 Test: The same location and plots were utilized during the 2000 season. The plot size, number of reps, and treatments were repeated as outlined in the 1999 test. Potash was applied October 20, 1999.

Three cuttings were measured for yields on May 30, July 13, and August 30, 2000 and the hay was baled in small rectangular bales. Each plot was picked up by a stack wagon and weighed separately utilizing commercial weigh pads.

Results and Discussion

1999 Test: The yields of green chop are found in Table I. The first cutting yields and the total of the three cuttings did show a significant difference (p=0.10) between no additional potash and adding potash. However there was no clear rate response since there was no significant difference between 66 lbs of potash per acre and 300 lbs.

1999 Weighing

Even though there was no significant differences among treatments in the second and third cuttings, the trend was there for higher yields when we added potash as compared to no additional potash.

1999 Alfalfa Potash

2000 Test: The yields of the small bales are also found in Table I. There was a significant difference among treatments with the first cutting at the 90 percent confidence level. However there was a significant difference at the 95 percent confidence level for the third cutting and the season total. The second cutting was the only one that did not show a significant difference at the 95 or 90 percent confidence level, but the yields were again higher for the addition of potash as compared to no additional potash.

Weighing 2000	Weigh Pads

Summary and Conclusions

The alfalfa yield results from 1999 and 2000 raises the question whether CSU recommendations for potash on alfalfa are accurate for the Western Slope of Colorado. Based on the results, we were unable to clearly define a rate response, however, the significant differences and the trends when there was no significant difference, strongly suggest that added potash above CSU's recommendations increases alfalfa yields.

The current plans are to continue testing at a different location or locations in 2001 and 2002 to gain enough information to determine the level of potash needed to maximize both alfalfa yields and profits.

Table I: Alfalfa Potash Yield Results

1999 Test (lbs/A Green Chop)
lbs Potash/A	lbs K20/A	First Cutting 2/	Second Cutting	Third Cutting 9/10/99	Total 2/
		6/8/1999	7/20/1999
0	0	8,525 B	9,413	6,091	24,028 B
66	40	10,000 A	10,112	7,027	27,138 A
133	80	9,464 A	10,352	7,066	26,882 A
300	180	10,340 A	10,759	7,610	28,709 A
2000 Test (lbs/A Small Bales)
lbs Potash/A	lbs K20/A	First Cutting 2/ 5/30/2000	Second Cutting 7/13/2000	Third Cutting 3/ 8/30/2000	Total 3/
0	0	2,026 B	3,301 A	2,884 B	8,812 B
66	40	2,954 A	3,605 A	2,932 B	9,491 AB
133	80	2,866 AB	3,789 A	3,080 AB	9,734 AB
300	180	3,058 A	4,297 A	3,611 A	10,965 A
1/ 2/ 3/	Treatment means with the same letter, or no letter, are not signigicantly different. Treatment means with the same letter are not significantly different (p<0.10) by analysis of variance. Treatment means with the same letter are not significantly different (p<0.05) by analysis of variance.

Colorado State University, U.S. Department of Agriculture and Delta, Mesa, Montrose & Ouray Counties cooperating. Extension programs are available to all without discrimination. No endorsement of products is intended nor is criticism of products mentioned.