POTATO (Solanum tuberosum, 'Russet Burbank') Effect of Planting Density

Transcription

1 POTATO (Solanum tuberosum, 'Russet Burbank') Effect of Planting W. R. Stevenson and R. V. James Dept. of Plant Pathology University of Wisconsin-Madison Madison, WI EVALUATION OF THE EFFECT OF POTATO PLANTING DENSITY ON YIELD AND WEED CONTROL - RUSSET BURBANK - HANCOCK, 1998: A trial was established April 27 at the Hancock Agricultural Research Station to obtain data for a second year on the effect of planting density on yield, quality and weed control. A variety of planned planting densities were used to recreate the variable stands that can result from seedpiece decay in grower fields. Data from these trials, along with data from seedpiece decay studies, will be used to help determine if compensation in fields with reduced stands can be sufficient to produce acceptable yield, and how poor stand in a field needs to be to justify replanting. US#1 size Russet Burbank tubers were mechanically cut and allowed to heal 5 days before planting. Plots consisted of four 20 foot-long rows spaced three feet apart. Each of the 20 potential planting positions in each row received either a seedpiece or a miniature marshmallow to mark an empty space. The position of seedpieces in each row of each plot was designed independently to result in the desired final planting density ranging from 20% to 100% of the normal planting density. A randomized complete block design with four replications was used. The four rows of each plot were planted at the same density, but all weed and yield data were taken from the center two rows only, to avoid interference from adjacent plots with different planting densities. The soil type was Plainfield loamy sand ph 6.2. Fertilizer consisted of 200 lb/a of broadcast before planting, 600 lb/a of banded in the row at planting, sidedress applications May 20 ( , 350 lb/a) and June 1 (34-0-0, 375 lb/a) and broadcast application of Cal-Sul, 500 lb/a, June 2. Insects were controlled with Admire (16./A) incorporated in the fertilizer at planting and foliar application of Asana XL, 5.8 fl./a, July 31 and August 8. Linex 50 DF (1.0 lb/a) was applied May 11 for weed control. Bravo Zn fungicide was applied on a standard schedule for early and late blight control (1.13 pt/a - June 25, July 3; 1.5 pt/a - July 10, 17, 24, 31; 1.75 pt/a - August 8, 14, 21, 27). To assess weed development at the different plot densities, percent control of major weeds was assessed visually on August 3 and all weeds were pulled from the center two rows of each plot on August 10 and the total fresh weight of weeds was recorded. Vines were killed with an application of Diquat, 1.0 pt/a, plus Peptoil, 1.0 qt/a on August 28. The two center rows of each plot were machine harvested September 11 (a total of 40 feet of row) and graded into US#1 size, undersize and culls. All potatoes in the US#1 category from each treatment plot were sorted using an optical size grader into six categories: < 4, 4-6, 6-10, 10-13, and >16. The 20 largest tubers from each plot were cut in half and examined for symptoms of hollow heart and internal browning and specific gravity was determined for a tuber sample from each plot. Rainfall measured during the growing season (inches) was: May, 3.0; June, 6.4; July, 2.5 and August, 6.5. An additional 19.4 inches of water was applied as overhead sprinkler irrigation in 37 applications (May 6 - September 2). The final plant stand closely approximated (within 2%) the desired planting density in every treatment. Plant stand significantly affected the weight of weeds harvested in individual plots. At stands of %, weed weights were similar, but at lower plant densities, weed weights significantly increased (Table 1 and Fig. 3). Weed weights were lowest in plots with % stands. Weed species appeared to respond somewhat differently to reduced stand densities. At stand densities below 60%, control of common lambsquarters, witchgrass and crabgrass steadily decreased. Yields were less responsive to stand reductions than anticipated (Table 2-3). Total yields and yields of US#1 tubers were statistically similar for stands of 50% and higher. Yield of undersize tubers steadily declined as stands were reduced. Total yield and yields of US#1 and undersize tubers were highest in plots with close to 100% stand (12-inch in-row spacing). The highest density plantings yielded the greatest proportion of < 6 tubers and the lowest proportion of tubers in the 6-13 category. The relationship between yield and plant stand is best described by a fourth order polynomial regression equation (Fig. 1-2) with yields dropping sharply at plant stands below 60%. These data suggest that a more ideal plant spacing in-row is greater than 12 inches. In terms of economic value of the crop, any losses in total yield are compensated by increases in tuber size and value of increasing tuber size (Table 5, Fig. 4-5). Loss of up to 40% stand from these plots did not appear to affect the crop profitability. Increasing weed growth as potato stand densities were reduced would quickly reach the point of being unacceptable to growers at harvest. Plant densities did not appear to affect the proportion of tubers exhibiting internal defects. We expected to see an increasing amount of internal defects as the planting densities declined, but this was not the case in these plots. Page 57

2 Table 1. Actual plant density observed and effect of planting density on weed weight and control of major weeds - Russet Burbank. Planting % Control of Major Weeds 2 Seed - pieces Planted / 10 of row Plant Observed 6/12 Weed Weight (Tons/ A) % Red Root Pigweed Common Lambsquarters 90 % % % % % % % % Pr > F 3 < 0.01 < 0.01 < < < Lsd NS 16.3 NS NS NS Fresh weight of all weeds in 2 center rows of each plot, 8/10/98, converted to tons/a. 2 Weed control estimate done by personnel from UW Dept of Horticulture, weed science program. 100 = complete control. 3 Analysis of variance was performed on data, and Fisher's protected least significant difference (LSD) was calculated. NS = not significant at the P = 0.05 (or P = 0.10) level. * = significant at P = 0.10 but not at P = Wild Buckwheat Carpetweed Hairy Nightshade Barnyard Grass Fall Panicum Witchgrass Small Crabgrass Table 2. Planting Effect of plant density on yield and proportion of US#1, undersize and cull potatoes - Russet Burbank. Seed - pieces Planted / 10 of row cwt/a Potato Yield Total US#1 Undersize 1 Culls yield 2 cwt/a % yield 2 cwt/a % yield 2 cwt/a % yield % % % % % % % % % Pr > F 3 < < <0.01 < Lsd NS NS Page 58

3 Table 3. Effect of planting density on size grades and specific gravity of US#1 potatoes - Russet Burbank. Planting Seed - pieces Planted / 10 of row US#1 cwt/a % < 4 % 4-6 Size Grades of US#1 Potatoes % 6-10 % % 6-13 % % > 16 Specific Gravity 100 % % % % % % % % % Pr > F 1 <0.01 < <0.01 <0.01 < Lsd * NS NS 1 Analysis of variance was performed on data, and Fisher's protected least significant difference (LSD) was calculated. NS = not significant at the P = 0.05 (or P = 0.10) level. * = significant at P = 0.10 but not at P = Table 4. Effect of planting density on quality of US#1 potatoes - Russet Burbank. Planting Seed - pieces Planted / 10 of row % of Tubers % of Tubers With Internal Browning with Hollow Heart 1 slight moderate severe Internal Browning Index 1, % % % % % % % % % Pr > F Lsd 3 NS NS NS NS NS 1 Tubers (20/plot) were cut lengthwise through the center to evaluate hollow heart and internal browning. 2 Internal Browning (IB) Index = (# tubers with slight IB x 1 + # tubers with moderate IB x2 + # tubers with severe IB x 3) x 100/20*3 where 20 is # tubers rated and 3 is the maximum possible score. Multiplying by 100 expresses this value as a percentage of the worst possible case (if all tubers were rated as 3). 3 Analysis of variance was performed on data, and Fisher's protected least significant difference (LSD) was calculated. NS = not significant at the P = 0.05 (or P = 0.10) level. * = significant at P = 0.10 but not at P = Page 59

4 Table 5. Effect of experimental treatment on value per acre - Russet Burbank potatoes. Gross Value of Yield Effect of Treatment on Value 1 Fresh Market 2 Processing 3 Fresh Market 2 Processing % % % % % % % % % Pr > F < <0.01 Lsd Gross value of standard (100% planting density) minus gross value for the treatment. 2 Typical 1998 fresh market pricing: 4-6. $6.50/cwt, $10.25/cwt, $12.50, >13. $12.00, < 4. and culls $.75/cwt. 3 Typical 1998 processing contract pricing: Base price is $4.80/cwt for 60% US#1, with 40% size and specific gravity of For each 1% above or below 60% (to a maximum of 75%; minimum of 40%) US#1 the price increases or decreases $0.01/cwt. For each 1% above or below 40% (to a maximum of 50%) size the price increases or decreases $0.03/cwt. For each.001 difference in specific gravity above or below (to a maximum gravity of 1.083), the price increases or decreases $0.02/cwt. Culls were not size graded in this experiment. It is assumed for these calculations that a similar proportion of culls would fall in the 6-13 range as US#1 s in this size range. 4 Analysis of variance was performed on data, and Fisher's protected least significant difference (LSD) was calculated. NS = not significant at the P = 0.05 (or P = 0.10) level. * = Difference between treatments were significant at P = 0.10, but not at P = Fig. 1 The effect of plant density on yield. 500 Yield (cwt/a) vs. Stand Total Yield Undersize US#1 Culls 450 Poly. (Total Yield) Poly. (US#1) 400 Poly. (Undersize ) Poly. (Culls) 350 cwt/a % Stand y = 3E-05x x x x R 2 = y = 3E-05x x x x R 2 = y = 2E-06x x x x R 2 = y = -1E-06x x x x R 2 = Page 60

5 Fig. 2 The effect of plant density on relative yield. Page 61

6 Fig. 4 The effect of plant density on crop value. Page 62