1997

POTATO SOIL FERTILITY EVALUATION

John Lancaster, Cooperator

Joe D. Janak, C.E.A.

SUMMARY:

Potatoes fertilized with an additional one and two cups of 0-20-0 fertilizer per 10 feet of row over the Texas A&M University Soils Lab recommendation produced 15 and 65 percent more pounds of potatoes respectively.

PROBLEM:

Due to favorable results in increasing onion size by sidedressing with superphosphate, the answer to the question was unknown whether the same treatment could benefit potatoes.

OBJECTIVES:

To demonstrate the effect of sidedressing superphosphate fertilizer applied at over and above the Texas A&M University recommendation levels to potatoes on a sandy loam soil.

MATERIALS/METHODS:

Three 20 foot long rows of Red Lasoda potatoes were planted on raised beds in the spring of 1997 using the principles of "The Square Foot Method" of Mel Bartholomew. Twenty four potato seed pieces were planted per row or one every 10 inches of row. All rows were fertilized as recommended by TAMU Soils Lab. Row #1 was sidedressed on both sides with an additional one cup of 0-20-0 fertilizer per 10 feet of row for each side of the row. Row #2 was sidedressed with an additional one cup per ten feet of row on only one side of the row.

Plant height was measured along with weight measurements for each treatment.

RESULTS:

Rainfall was excessive and nearly 30 inches by the harvest time but potatoes were dug and saved. The plot sidedresed twice was 50 percent taller producing 65 percent more potatoes than the non-sidedressed plot. The plot sidedressed once was 21 percent taller and produced 15 percent more potatoes than the non-sidedressed plot. Additionally, the largest 5 and largest 10 potatoes of the double sidedressed plots were 45 and 63 percent heavier than the largest of the non-sidedressed plot. (See Table 1)

Table 1. Potato yield and results from additional sidedressings of superphosphate fertilizer. John Lancaster, cooperator, Victoria County, TX 1997.

FERTILIZER	PLANT HEIGHT IN INCHES % CHANGE		WEIGHT OF TOP 5 IN GRAMS % CHANGE		WEIGHT OF TOP 10 IN GRAMS % CHANGE		POUNDS HARVESTED PER 20 FOOT ROW % CHANGE
2 cup 0-20-0	21	50%	2000	45%	3900	63%	39.5	65%
1 cup 0-20-0	17	21%	1825	33%	3100	29%	27.5	15%
Control	14	-	1375	-	2400	-	24	-

ECONOMIC ANALYSIS AND IMPACT:

The application of superphosphate 0-20-0 fertilizer proved to be economical for the garden producer.

CONCLUSION:

For home production in the garden setting, it is economical to sidedress with additional superphosphate fertilizer on a sandy soil. Be careful though as continual applications of high levels of superphosphate fertilizer may accumulate to levels that make other nutrients unavailable limiting growth.

ACKNOWLEDGMENTS:

Appreciation is expressed John Lancaster for coordinating and evaluating this demonstration.