Mid-Season P Fertilization Effects on Potatoes

Final potato tuber yields are a function of tuber growth rates and the duration of the tuber growth period, particularly for the indeterminate potato varieties. Nutrient uptake should be continuous until the start of normal plant maturation since the tubers function as major nutrient sinks during their growth. Nutrient uptake rates less than those required for tuber growth will cause the mobile nutrients to be translocated from the other plant parts to the tubers, eventually causing a premature canopy senescence. Final tuber yields will be reduced if this senescence starts when the environmental conditions are still favorable for growth. Nutrient uptake rates can slow or stop during the maturation growth stage since tuber growth during this period mainly comes from the translocation of dry matter and nutrients from the vegetative portions of the plant to the tubers

Indexes of Sulfur Deficiency in Alfalfa. I. Extractable Soil SO}4{-S

Sulfur deficiencies occur on many of the undeveloped agricultural soils found in the mountain valleys of the western United States; however, the majority of the S soil-test correlation studies have been conducted on leached and weathered soils. Identification of S deficiency on alfalfa (Medicago sativa L.) growing in three mountain valleys permitted the collection of S soil-test correlation data for these undeveloped soils. This paper reports the relationships found between extractable soil SO?-S levels and the response of alfalfa to S fertilization. Soil samples were taken from 13 experimental sites before active plant growth commenced in the spring in 30-cm depth increments to 92 cm. Soil SO?-S was extracted by water, 0.1 M LiCl, and 0.032 M KH?PO? and measured by the methylene-blue reduction method. Significant correlations were obtained between the SO?-S extracted by all three extractants from the 0- to 30-cm soil layers and relative forage yields and total S uptake by the first harvest of alfalfa at early bloom. Critical soil SO?-S levels of 3.0, 3.0, and 4.0 ppm in this soil layer were found when extracted by water, LiCl, and KH?PO?, respectively. Inclusion of KH?PO?-extractable SO?-S to 92 cm did not improve the curvilinear regression relationships, nor did inclusion of percent soil organic matter. Increasing the soil:extractant ratio from 1:2 to 1:3 did not significantly change the amount of SO?-S extracted by the KH?PO? solution. The 0.1 M LiCl solution is recommended for extracting SO?-S from soils with relatively small amounts of absorbed SO?-S

Indexes of Sulfur Deficiency in Alfalfa. II. Plant Analyses

Both soil and plant analysis are diagnostic tools used in identifying S deficiencies; however, soil tests evaluating soil S availability levels are not always successful and deficiencies must then be identified by plant analysis. In addition, the diagnostic tool must be correlated to crop responses under various growing conditions to be useful. Identification of S deficiency on alfalfa (Medicago sativa L) in southern Idaho permitted the collection of correlation data for both S soil tests and plant analyses. The S soil test correlation data has been previously reported (Aron. J. 66:578-581, 1974). This paper reports the relationships found between the plant S indexes of total S, SO?-S and total (N/S) ratio, and the response of alfalfa to S fertilization. All data were evaluated by correlation analyses. The total S and SO?-S concentrations and the total (N/S) ratio were all found to be satisfactory indexes of S deficiency in whole alfalfa at early bloom. Maximum forage yields were obtained when the tops contained between 0.15 to 0.20% S or 0.05% SO?-S. Total S and SO?-S were related and readily interchangeable as indexes. Increases in total S above 0.14% S resulted from the accumulation of SO?-S. Yield responses to S fertilization were obtained when the total (N/S) ratio was greater than 17 to 18. Total N and total S were not related, but protein N increased linearly as protein S increased. The protein (N/S) ratios were not constant and increased from 17 to 23 as the degree of S deficiency increased

Lime effects on P availability

Nutrient uptake can be predicted by assuming that plant roots absorb nutrients from the soil solution and that the rate of absorption is dependent upon the nutrient concentration in the soil solution (2). The root growth rate also affects P uptake since uptake is directly proportional to active root surface area, particularly new root hairs. The three main soil characteristics that describe the P supply to the plant root are: (a) P concentration in the soil solution before growth, (b) the ability of the soil to replenish the P in the soil solution, the buffer power, and (c) the P diffusion rate through the soil. The diffusion process is the main supply mechanism for P reaching the root surface. There are several factors that directly or indirectly influence soil and fertilizer P availability. These include soil, fertilizer, management, and environmental characteristics. Additional details of the complex reactions and interactions are beyond the scope of this paper, but can be found in recent reviews (4, 7). A nutrient survey showed that 25 out of 123 potato fields in Idaho had soil test P concentrations (STPC) more than adequate, but petiole PO4-P concentrations considered to be deficient (11). The significance of the petiole PO4-P concentration in relation to plant growth needs have been better defined (12) since that report. This paper presents data showing the effects of lime on soil solution P concentrations and P uptake by plants

Plant analyses and interpretation

Plant analysis historic beginnings are generally attributed to T. de Saussure (1804) following studies by van Helmont, Joseph Priestly, Henry Cavenish, and Antonine Lavoisier. de Saussure showed that the composition of plant ash varied with the part analyzed, with the age of the plant, and with the soil upon which the plant grew. The ash was chiefly composed of alkalis and phosphates. Erasmus Darwin in his 1800 book, Phytogia: The Philosophy of Agriculture and Gardening (London, J. Johnson) wrote that both nitrogen (N) and phosphorus (P) were essential components of plants. In 1833, the Fifth Duke of Richmond showed that the value of bone meal fertilizing was due to its P component rather than calcium (Ca), although Justus von Liebig (1852) is generally considered the father of soil fertility. Readers interested in additional historic information should consult Ulrich (1948), Bear (1948), and Russell (1976)

Lime effects on phosphorus availability in a calcareous soil

Crop yields are sometimes reduced on irrigated calcareous soils with elevated lime concentrations. This study was conducted to determine the influence of lime on P availability. The effects of acid-equivalent lime concentrations and P fertilization rates on NaHCO3-soluble P, anion resin-extractable P, P-adsorption isotherms in 0.01 M CaCl2, and P uptake by sudangrass [Sorghum bicolor (L.) Moench] and potato (Solanum tuberosum L.) were investigated in the greenhouse on soil samples from the Portneuf silt loam (coarse-silty, mixed, mesic Durixerollic Calciorthid). Plant P uptake was increased by P fertilization and decreased by increasing lime concentration. Phosphorus uptake was curvilinearly related to solution P (extracted by 0.01 M CaCl2). Solution P concentrations increased linearly as the resin-extractable P/equilibrium buffer capacity (EBC) ratio increased, where EBC is the slope of the P-adsorption isotherm at the indigenous equilibrium P concentration. The EBC increased as the lime concentration increased. Phosphorus applications increased solution P and resin-extractable P and decreased EBC within a given lime concentration. These data indicate that the soil-test P concentration or P fertilization rate should increase as the lime concentration increases to provide the same degree of P availability and plant P uptake in this calcareous soil

Nutritional requirements of potatoes

Plant nutrition is the practice of providing to the plant the right nutrient, in the right amount, in the right place, at the right time. This paper gives an overview of the roles that each of the 16 essential nutrients have in plant nutrition, their relative mobility as related to deficiency symptom expression, and what is generally known about nutrient responses to field applications on potatoes (Solanum tuberosum L.) in the USA and Canada. Maintaining high crop yields with minimum nutrient losses to the environment is and will continue to be a significant challenge to the potato producer. Additional nutritional research efforts in genetically modified plants, precision agriculture, food quality and safety, fertilizer impurities, and other management concerns should significantly help the producer in this effort

Phosphorus Fertilization Economics

Fertilizer costs have become important factors in crop production in recent years because of (a) increased energy costs associated with fertilizer manufacturing and (b) material shortages. Since this trend will probably continue, it is important that fertilization practices maximize economic returns and fertilizer efficiencies. We have been evaluating the P fertilization needs of some of'the major crops grown in southern Idaho since 1973. This report compares the increased net crop value resulting from P fertilization at different soil test P levels

Soil management practices

Soil management practices affect soil resources obviously, but those practices also affect water and air resources and the plants and animals that depend upon those resources. Good soil management builds soil quality, maintains or improves water and air quality, and supports plant, animal, and human life (NRCS, 1996a). Minimizing soil erosion, increasing water infiltration, and promoting biological activity through good management ultimately produces a soil with physical and chemical characteristics consistent with parent material, topography, and climat

Measuring Soil Nitrogen Mineralization Under Field Conditions

The amount and rate of soil N mineralization are important components that can be used to predict preplant N fertilizer application and to evaluate the need for N fertilization during crop growth. This study's purpose was to evaluate the buried polyethylene bag technique as a method for characterizing the N mineralized under field conditions during the cropping season. Soil (Xerollic Calciorthids) was placed in polyethylene bags and buried in the 0 to 45 cm root zone of fallowed soils and where corn (Zea mays L.) and potato (Solanum tuberosum L.) were being grown. The NO?-N content of the soil in the bags was compared with that in the root zone at selected time intervals (10 to 14 days) from April to October. The soil NO?-N concentrations in the buried polyethylene bags were similar to those in irrigated fallow soils from April to October after correction for different soil water contents. The N-mineralization rate between sampling intervals had an average temperature coefficient (Q??) of 2.3 between 10 C and 30 C. The relative N mineralization rate was proportional to the soil water content expressed as a percentage of the available water-holding capacity. The N uptake by corn and potato crops predicted from NO?-N changes in the rooting zone and in the buried polyethylene bags resembled those measured by plant sampling. The buried polyethylene bag technique has potential for monitoring the soil N mineralization process during the cropping season and for estimating N uptake by crops. It also provides an alternative method for estimating soil N availability for future crops and its use should maximize N-fertilizer efficiencies