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1 This article was downloaded by: [University of Idaho] On: 22 May 2013, At: 13:06 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK Communications in Soil Science and Plant Analysis Publication details, including instructions for authors and subscription information: Nutrient Management Practices Used in Potato Production In Idaho Loy Pehrson a, R. L. Mahler a, E. J. Bechinski a & C. Williams a a University of Idaho, Moscow, Idaho, USA Published online: 05 Apr To cite this article: Loy Pehrson, R. L. Mahler, E. J. Bechinski & C. Williams (2011): Nutrient Management Practices Used in Potato Production In Idaho, Communications in Soil Science and Plant Analysis, 42:8, To link to this article: PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

2 Communications in Soil Science and Plant Analysis, 42: , 2011 Copyright Taylor & Francis Group, LLC ISSN: print / online DOI: / Nutrient Management Practices Used in Potato Production In Idaho LOY PEHRSON, R. L. MAHLER, E. J. BECHINSKI, AND C. WILLIAMS University of Idaho, Moscow, Idaho, USA Introduction Sound nutrient-management practices are an essential component of modern intensive potato (Solanum tuberosum) production systems. Economic and environmental issues are requiring Idaho potato producers to use management practices that are effective and efficient to remain competitive in the market. Identical potato production management surveys were conducted in 1997 and again in to determine current nutrient management practices used by Idaho potato growers. This Dillman mail-based survey collected data that were used to determine current nutrient-management strategies and changes that have occurred over the past 10 years. In , more than 77% of growers used preplant soil tests for determining nitrogen (N) application needs. More than 96% of potato growers relied on petiole analysis of potato plant tissue for N management during the growing season. Changes have occurred in only 7 of 28 nutrient-management categories evaluated in the past 10 years, indicating maturity rather than evolution in nutrient management strategies for potatoes. Over the past 10 years, application rates of N have decreased, while potassium (K) rates have increased. There has been a decrease in the number of growers who plant legumes in crop rotation as a source of N. The use of nitrification inhibitors, precision fertilizer management, and application of manure to potato fields has increased in the past 10 years. The overall lack of changes in nutrient management in the past 10 years may indicate that nutrient-management strategies for potatoes in Idaho are mature and successful. Keywords Micronutrient management, nitrogen management, phosphorus management, plant tissue diagnosis, potassium management Potato (Solanum tuberosum) production was first documented more than 7,000 years ago in the Andean region of South America. The indigenous Andean viewed the potato as a staple food and believed that it had the power to heal many ailments. The Spanish rulers probably exported potatoes to Europe in the 1500s. Because of the high starch and nutrient content, with more calorie production per acre than many grains, potatoes were viewed as an important food source and consequently became widely produced around the globe. The potato arrived in North America in the early 1700s (Stark and Love 2003). The first production of potatoes in Idaho was documented in the 1830s near Lapwai, Idaho. A Christian missionary, Henry Spalding, introduced the potato to the Nez Perce Received 30 July 2009; accepted 13 May Address correspondence to Robert L. Mahler, P. O. Box , PSES, University of Idaho, Moscow, ID bmahler@uidaho.edu 871

3 872 L. Pehrson et al. Indians as a means of producing sustainable quantities of food, helping pave the way for the Idaho potato industry as we know it today (Davis 1992). In 2006, Idaho produced approximately 31% of the fall potato crop (121,820 kcwt) in the USA. The Idaho potato industry is important to Idaho s economy and is valued at more than $700,000,000 on an annual basis (NASS 2006). The success of the Idaho potato industry relies heavily on the use of chemical (inorganic) sources for supplying adequate nutrients. Because potatoes have shallow root systems and are usually grown on soils with low water-holding capacities, they are more susceptible to nutrient losses than many other crops. Nutrient-management programs can be both efficient and effective when they are designed to meet the requirements of potato plants during the growing season by providing appropriate amounts of nutrients at the most beneficial times for plant growth and tuber development. Exceeding or failing to meet plant nutrient needs at specific growth stages can result in yield reductions, poor tuber quality, and unwanted environmental consequences (Stark and Love 2003). In 1997, the University of Idaho sustainable agriculture team conducted an extensive survey to identify nutrient-management practices used by Idaho potato producers. The survey examined management strategies for water, nutrients, and agronomic practices (Mahler et al. 1998a, 1998b, 1998c). To determine changes in nutrient management in the past 10 years, a survey identical to the 1997 version was conducted again in The data from these surveys will serve as tool to understand how and if nutrient management has changed in Idaho. Materials and Methods A 25-question survey was designed to assess producer practices about water, nutrient, agronomic, and economic management in Idaho potato production in 1995 by the University of Idaho sustainable agriculture team (Mahler et al. 1998a, 1998b, 1998c). Five questions specifically dealing with nutrient management are evaluated in this study. This survey instrument was used in both 1996 and In addition to the five survey questions, the following demographic information was collected: number of acres planted to potatoes, age, education, gender, and gross farm sales for the previous cropping year. Survey Logistics In , 500 producers were set as the target sample population. The Dillman mail survey approach methodology was used in this study (Dillman 2000). Surveys were sent to 470 of 840 growers who appeared on the Potato Growers of Idaho mailing list. The survey process was designed to yield a completed return rate in excess of 50%. Based on the sample size of 470, if more than 235 surveys were returned, the sampling error could be assumed to be less than 4%. Four mailings were used to approach the desired return rate. Data Analysis The survey responses were coded and entered into a Microsoft Excel spreadsheet. The data were separated into columns and copied to SAS, a statistical software package (SAS 2004). Data that were missing or incorrect were excluded from the analysis. The data were analyzed by SAS software on two levels. The first level of analysis produced frequencies of responses for each question and their associated percentages. The second level of analysis evaluated interactions, which isolated how subgroups (age, acres,

4 Nutrient Management in Potatoes 873 gender, education, and gross farm sales) of survey respondents related to specific questions. The significance of the interactions was determined by using a chi-square test at a significance level of 5%. The data were compared to the 1997 survey results (Mahler et al 1998a, 1998b, 1998c). The nutrient-management questions in both surveys were identical so paired-t test comparisons were used to statistically evaluate the data over time. Results and Discussion The Idaho potato producers practices survey attained a return rate of 45.7% (215 either fully or partially completed and returned out of 470). With 215 surveys returned completed, the sampling error was reduced to ±4.5%. While the target return rate of 50% was not achieved, the survey data were still considered statistically meaningful, because responses were received from more than one quarter of all potato growers in Idaho (215 out of 810). Demographics The demographic data captured included number of acres planted to potatoes, age, level of education, gender, and 2004 gross farm sales. Two hundred fourteen of the 215 respondents were male. Survey respondents ranged in age from 28 to 74. Sixty-three percent of the respondents were in the 40 to 59 age group. Formal educational levels of the respondents ranged from high school graduate (or GED) to graduate degrees at universities. More than 80% of the respondents had formal education beyond high school. Based on the 2000 Idaho census, the average education level for potato growers was greater than the Idaho public as a whole (81% vs. 43% statewide education beyond high school) (U.S. Census Bureau 2000). Sixty percent of the potato growers surveyed usually planted more than 250 acres of potatoes on an annual basis. More than 83% of the respondents reported gross farm sales exceeding $250,000 for the year Almost 11% of respondents earned gross farm sales between $100,000 and $249,000, while less than 7.0% of the respondents had gross sales of less than $100,000. Nitrogen, Phosphorus, and Potassium Application Rates The majority of potato producers applied more than 200 lbs of nitrogen (N) per acre. As seen in Table 1, few growers added less than 100 lbs of commercial N per acre. More than 76% of producers applied more than 150 lbs of phosphorus (P) per acre to potatoes, while fewer than 6% applied less than 50 lbs (Table 1). A significant interaction (P =.0004) was found between the annual amount of P applied to potato fields and the gross farm sales of Idaho potato producers as more than 78% of growers with farm income greater than $100,000 used more than 150 lbs of P per acre. In contrast, fewer than 45% with farm incomes less than $100,000 use more than 150 lbs of P per acre. More than 76% of growers applied more than 100 lbs of K per acre annually with fewer than 9% applying less than 50 lbs (Table 1). Nutrient-Management Practices The majority of survey respondents either always or usually used the following nutrient management practices: (1) determined N fertilizer application rates via preplant soil

5 874 L. Pehrson et al. Table 1 Average annual nitrogen, phosphorus, and potassium application rates used on potatoes by growers in Idaho based on the Idaho Potato Producers Survey Nutrient Annual application rate (lbs/acre) Percentage applied Nitrogen < to to to to to to > Phosphorus < to to > Potassium < to to to > sampling, (2) split total N applications between preplant and top-dress or side-dress applications, (3) took a soil sample for P management, (4) took a soil sample for K management, (5) kept permanent written records of fertilizer applications, (6) used a professional consultant to determine nutrient needs in potatoes, and (7) provided N credits for legumes and manures previously applied to their field (Table 2). Based on the Idaho potato producer s survey, more than 92% of southern Idaho potato growers either always or usually used preplant soil sampling to determine N application rates. More than 90% of growers split their total N applications between preplant, side-dress, and/or top-dress applications. More than 87% of growers took soil samples for P and K management. More than 93% of growers kept permanent records of fertilizer applications. More than 87% of growers used a professional consultant to determine nutrient needs for potatoes. More than 61% of growers provided N credits for legumes and manures previously grown/applied to potato fields. A majority of Idaho potato growers only sometimes or never used the following nutrient management practices in : (1) planting legumes in crop rotation as a source of N, (2) use variable (precision) fertilizer management, (3) applying manure to potato fields, or (4) using nitrification inhibitors (Table 2). The occasional use of legumes in crop rotation as a source of N may be linked to the low economic value of short-term profitable legumes (e.g., beans) other than alfalfa, compared to planting the more profitable cereals and other grains that require a longer growing season. Although not widely used, precision fertilizer management is gaining in recognition and popularity. The relatively low use of this technology may be due to type of fertilizer application equipment growers own or have access to. Currently the most common type of precision nutrient application is done via irrigation, more commonly known as fertigation (>80%).

6 Nutrient Management in Potatoes 875 Table 2 Use of nutrient management practices by potato growers in southern Idaho based on the 2006 Idaho Potato Producers Survey How often do you use the following Frequency (%) practices as part of your nutrient management? Always Usually Sometimes Never Determine nitrogen fertilizer application rates via preplant soil sampling Split total nitrogen applications between preplant and top-dress or side-dress applications Take a soil sample for phosphorus management Take a soil sample for potassium management Keep permanent written records on fertilizer applications Use a professional consultant to determine nutrient needs in potatoes Provide nitrogen credits for legumes and manures previously applied to your field Plant legumes in rotation as a source of nitrogen Use variable (precision) fertilizer management Apply manure to your potato fields Use nitrification inhibitors Almost half of potato growers reported that they never applied manure to potato fields, with an additional 44% only sometimes applying manure (Table 2). The infrequent use of manure as a nutrient source for potatoes is most likely linked to two different reasons: (1) the lack of availability of manure in some locations and (2) some potato grower contracts may prohibit the use of manure because of the risk of introducing diseases and/or nematodes to the potato crop. The use of nitrification inhibitors (NI) by potato growers is not common. Nitrification inhibitors are only effective on fertilizers that contain or are converted to ammonium (urea) by inhibiting the conversion of ammonium to nitrate. The limited use of this practice may be in part due to (1) low effectiveness of the practice or (2) the greater cost-effectiveness of adding a little extra N fertilizer to compensate for leaching than paying for the NI. The cost of using the NI must be offset by reducing the N recommendation by an equal cost or an increase in yield or quality attributable to NI use. Soil Sampling for Phosphorus and Potassium There were significant interactions between growers who took soil samples for P(P = ) and/or K (P = ) management and their greatest level of education (Table 3). More than 60% of all growers with an education ranging from high school

7 876 L. Pehrson et al. Table 3 Interaction between growers who take a soil sample for P and/or K management and education level of growers based on the Idaho Potato Producers Survey (P, P value =.0217; K, P value =.0052) Education level (%) Frequency HS grad/ged Post HS/vo-tech Some college College graduate Graduate school Phosphorus Never Sometimes Usually Always Potassium Never Sometimes Usually Always graduate to graduate school always took soil samples for P and K management. Less than 2% of growers with some college or more education never used soil samples for P and K management. Conversely, just more than 10% of growers with only a high school education never used this practice. Nitrogen Credits A significant interaction (P = ) between growers who provided N credits for legumes and manures previously applied to potato fields and the age of the Idaho potato producer was observed. The age of the grower had an effect on the frequency of providing N credits. Growers between the ages of 50 and 69 were more likely to always provide N credits (about 50%), while growers aged 30 to 39 (<42%) and older than age 70 (<34%) were less likely to provide N credits. Legume Nitrogen Source There was a significant interaction (P = ) between growers who planted legumes in their crop rotation as a source of N and the total acres planted to potatoes by Idaho producers. Growers who had less than 200 acres planted to potatoes (>80%) were the most likely to sometimes, usually, or always plant legumes as an N source. Forty percent of the growers with 200 to 299 acres planted to potatoes never plant legumes in their crop rotation. This interaction may be explained by the fact that the smaller acreage growers use less commercial N fertilizer and thus are more reliant by choice (organic) or need to get N from legumes. Also, growers who planted more acres of potatoes may not have the land capacity to plant a multiyear legume and still maintain the high number of acres planted to potatoes.

8 Nutrient Management in Potatoes 877 Micronutrients The majority of respondents to the potato survey have applied micronutrients to their potato fields in the past 5 years. More than 93% of the respondents have applied zinc (Zn) at least once in the past 5 years. Manganese (Mn), copper (Cu), boron (B), and iron (Fe) have been applied in the past 5 years by 85.1, 80.9, 85.6, and 72.6%, of the potato survey respondents, respectively. A significant interaction (Zn P = <0.0001; Mn P = <0.0001; Cu P = ; B P = ) was found between the growers who have applied Zn, Mn, Cu, and/or B in the past 5 years and the total number of acres planted to potatoes. The vast majority of growers who have more than 50 acres planted to potatoes have applied micronutrients to their potato fields in the past 5 years. Conversely, fewer than 50% of growers with less than 50 acres have applied Zn, Mn, Cu, and/or B in the past 5 years. More than 90% of growers who planted 150 to 200 and 250 to 300 acres of potatoes have applied Zn, Mn, Cu, and B in the past 5 years. Petiole Sampling More than 96% of Idaho potato producers used petiole sampling during the growing season to determine potato N needs. Petiole sampling is used to identify deficiencies, sufficiencies, or excesses based on research-determined optimal nutrient levels. More than 80% of growers take between one and eight petiole samples on average during the growing season (Table 4). This observation concurs with the recommended scientific procedure of using petiole samples to determining potato N needs throughout the growing season. The actual frequency of petiole sampling is a function of the length of the growing season. In southwestern Idaho, where the growing season is longer because of a warmer climate, up to 14 petiole samplings are made. Conversely, the shorter growing season in southeastern Idaho limits the petiole season to about 8 weeks. Growers are advised to collect petiole samples on a weekly basis during the tuber growth period (Stark and Love 2003). Therefore, the actual optimum number of sampling times is a function of the length of the growing season. A significant interaction was observed (P = ) between the number of petiole samples collected during the growing season to determine potato N needs and total farm sales. The majority of growers with less than $250,000 in gross farm sales took three or Table 4 Average number of times potato petiole samples are taken during the growing season to determine potato N needs by the respondents of the Idaho Potato Producers Survey Number of petiole samples Percentage collecting Never 3.8 1, 2, or 3 times times times times times or more 6.2

9 878 L. Pehrson et al. fewer petiole samples during the growing season. In contrast, more than 72% of growers who had more than $250,000 in farm sales took six or more petiole samples during the growing season to determine potato N needs. Besides taking petiole samples for potato N content, a majority of growers took at least one petiole sampling to determine P and K content for growing potatoes. More than 90% of growers took petiole samples for P and more than 86% took samples for K. Ten-Year Changes This survey conducted in was identical to questions asked in a survey originally conducted in Answers to each question were statistically analyzed to determine changes in the 10-year period between the surveys. The responses to questions in 1997 and were statistically similar for all but seven aspects of nutrient management. Statistical differences between 1997 and were found for questions about (1) annual N application rate, (2) annual K application rate, (3) planting legumes in rotation as a source of N, (4) use of nitrification inhibitors, (5) use of variable (precision) fertilizer management, (6) application of manure to potato fields, and (7) frequency of collecting potato petiole samples for determining potato N needs. Only 7 of the 28 nutrient management practices surveyed (N application rate; P application rate; K application rate; use of consultant services; use of legumes in rotation; preplant soil N test; split N application; use of N credits; use of nitrification inhibitors; use of precision fertilizer management; use of manures; soil sample for P management; soil sample for K management; written fertilizer records; collecting plant tissue samples; petiole evaluation for N; petiole evaluation for P; petiole evaluation for K; Zn applications; Mn applications; Cu applications; B applications; Fe applications; soil sampling for Zn; soil sampling for B; soil sampling for Mn; soil sampling for Fe; and soil sampling for Cu) have changed in the past 10 years. Consequently, the survey results emphasized the stability of nutrientmanagement practices over the past decade. However, this section discusses the seven statistically significant changes in nutrient management that have occurred more than the past 10 years. The annual application rate of N has changed in the past 10 years. A significant difference (P = ) was found between the percentages of 1997 and 2006 growers who apply between 100 and 150 lbs of N to potato fields annually (Table 5). In 1997, less than 6% of growers indicated they apply 100 to 150 lbs N, while in more than 12% of growers applied this amount of N. These changes could be the result of improved fertilizer management programs that incorporate split N applications as well as improved fertilizer placement technologies. Placement of fertilizer for optimum uptake can improve N-use efficiency (NUE) and offset costs and environmental nutrient losses. Differences of less than 5.5% were not statistically significant (Table 5). The annual application rate of K was different in 1997 and A significant difference (P = ) was found between growers who apply between 50 and 100 lbs K to potato fields annually (Table 6). In 1997, more than 25% of growers applied between 50 and 100 lbs K, while in less than 16% of growers applied the same amount. Basically, by growers were applying more K to potatoes. This change may be related to declining soil-test K levels in southern Idaho soils. A significant difference (P = ) was found between 1997 growers and growers who plant legumes in crop rotation as a source of N (Table 7). The number of growers who indicated that they usually plant legumes in their crop rotation has decreased since Less than 13% of growers usually plant legumes in

10 Nutrient Management in Potatoes 879 Table 5 Comparison of the annual N application rate used on potatoes by growers in southern Idaho in 1997 and based on the Idaho Potato Producers Survey Percentage applying Annual N application rate (lbs/acre) Difference Less than to to to to to to More than Table 6 Comparison of the annual K application rate used on potatoes by growers in 1997 and based on the Idaho Potato Producers Survey Percentage applying Annual K application rate (lbs/acre) Difference Less than to to to rotation while almost 20% of 1997 growers usually used the practice. The reasons for this difference are unclear but may be related to retreating prices of large-seeded legumes, such as dry beans, in the past decade. A significant difference (P = ) was found between 1997 growers and growers who never used nitrification inhibitors for potato production (Table 7). In 1997, more than 68% of growers indicated they never used nitrification inhibitors for potato production. The number of growers in that reported they never used nitrification inhibitors declined to less than 57%. This difference in the increased use of nitrification inhibitors may be related to the rising costs of N fertilizer over the past several years (Hopkins et al. 2003). Significant differences (P = ) were found between 1997 growers and growers who never and sometimes used variable or precision fertilizer management (Table 7). In 1997, more than 51% of growers reported that they never used variable or precision fertilizer management. Conversely, in 2006 less than 38% of growers reported they never used this type of fertilizer management. About 20% of growers in 1997 reported that they sometimes used variable or precision fertilizer management, while less than 34%

11 880 L. Pehrson et al. Table 7 Comparison of the use of legumes in crop rotations to provide a source of N, the use of nitrification inhibitors, the use of precision fertilizer management, and the application of manure in 1997 and based on the Idaho Potato Producers Survey Parameter Frequency 1997 (%) 2006 (%) Difference (%) Legumes in rotation Nitrification inhibitors Precision fertilizer management Application of manure Never Sometimes Usually Always Never Sometimes Usually Always Never Sometimes Usually Always Never Sometimes Usually Always of growers in reported the same. The increased use of variable or precision fertilizer management over this 10-year period was expected because of the advancement of new technologies. Significant differences (P = <0.0001) were found between 1997 growers and growers who never and sometimes applied manure to potato fields (Table 7). Growers in were more likely (>43%) to sometimes apply manure to potato fields than in 1997 (<33%). Furthermore, more than 61% of 1997 growers never applied manure, while less than 46% of growers never applied manure to potato fields. This difference may be due to the rising costs of synthetic N sources, which forces farmers to use alternatives and the increased production of organically grown potatoes. Additionally, the abundance of manure in southcentral Idaho has probably increased over the past 10 years as a result of an expanding dairy industry. The average number of potato petiole samples that were taken during the growing season has changed in the past 10 years. When evaluating the responses to the 1997 and versions of the Idaho potato producers survey, significant differences

12 Nutrient Management in Potatoes 881 Table 8 Comparison of the average number of times potato petiole samples are taken during the growing season to determine potato N needs in 1997 and based on the Idaho Potato Producers Survey Number of Percentage collecting petiole samples Difference Never , 2, or 3 times times times times times or more (P = ) were found for growers who collected petiole samples one, two, or three times and growers who collected at least 10 samples during the growing season for determining N needs (Table 8). In 1997, less than 11% of growers collected petiole samples one, two, or three times during the growing season compared to 18% of growers in Additionally, less than 7% of growers in collected 10 samples during the growing season, while in 1997, more than 17% of growers collected 10 samples. The reduction in the percentage of growers who collected petiole samples 10 times per year may be related to geography. There were fewer potato growers in southwestern Idaho in 2006 as a percentage of potato growers in the state compared to 1997 numbers. The longer growing season in southwestern Idaho has traditionally resulted in more petiole samples being collected. Conclusion The nutrients N, P, K, and micronutrients are intensively managed by Idaho potato producers. The vast majority of potato growers utilize both soil and plant diagnostics to determine optimum nutrient inputs. Since 1997, only seven significant nutrient-management changes have occurred. The application rate of N, the frequency of petiole samples taken, and the use of legumes in rotation as a source of N have decreased. Compared to 1997 practices, the application rates of K, the use of NIs, use of variable fertilizer management, and the application of manure have increased. From a plant nutrition standpoint, potatoes are the most intensively managed crop in Idaho. It is common for growers to rely on both soil sampling and analysis and plant tissue diagnostics to produce this crop. Both diagnostic practices have been standard for more than 40 years. Growers have traditionally applied fertilizer N at planting based on a soil test with the goal of achieving nitrate N contents in excess of 24,000 ppm in petioles of young potato plants. As the growing season advances, weekly petiole sampling and analysis is used to transform the potato plant growth strategy from that of vegetative growth to tuber initiation and then bulking. This nutrient program has resulted in high-quality potatoes and excellent yields considering the climate-limited growing season. The use of petiole analysis

13 882 L. Pehrson et al. to spoon feed tuber growth during the growing season has also yielded NUE values of more than 70%. One could argue that this is an ideal nutrient-management system that should be copied to the production of other high-value crops. Overall, from a nutrient-management standpoint, the Idaho potato industry is a mature industry. Growers are essentially using the same management practices as in 1997 with only small changes in specific practices. This nutrient-management system is apparently working well and is not in need of any major changes from a successful production standpoint. It could be argued that lack of change in nutrient management may be indicative of a relatively sustainable agricultural system (Mahler et al. 1996). References Davis, J. W Aristocrat in burlap: A history of the potato in Idaho. Boise: Idaho Potato Commission. Dillman, D. A Mail and Internet surveys: The tailored design method. New York: John Wiley & Sons. Hopkins, B., J. Ellsworth, and P. Patterson Skyrocketing nitrogen prices and potato production (University of Idaho Agricultural Economics Extension Series No. 3 4). Available at Mahler, R. L., E. J. Bechinski, C. Williams, and K. A. Loeffelman Sustainable agriculture: Concepts, promises and challenges. Moscow: University of Idaho. Mahler, R. L., E. J. Bechinski, C. Williams, and K. A. Loeffelman. 1998a. Idaho potato producers practices survey. Moscow: University of Idaho. Mahler, R. L., E. J. Bechinski, C. Williams, and K. A. Loeffelman. 1998b. Idaho potato producers practices: Survey for nutrient management. Moscow: University of Idaho. Mahler, R. L., E. J. Bechinski, C. Williams, and K. A. Loeffelman. 1998c. Idaho potato producers practices: Survey for water and crop management. Moscow: University of Idaho. NASS Fall potatoes. Washington, D.C.: U.S. Department of Agriculture. Available at SAS SAS/STAT user s guide. Cary, N.C.: SAS Publishing. Stark, J. C., and S. L. Love Potato production systems. Moscow, Idaho: University of Idaho Agricultural Communications. U.S. Census Bureau Idaho census: Social characteristics. Washington, D.C.: U.S. Census Bureau. Available at qr_name=dec_2000_sf3_u_dp2&ds_name=dec_2000_sf3_u&geo_id=04000us16