Soil Heat Units Research Articles

Soil solarization enhances growth and yield in dry beans

Dry beans are one of the most important crops in Mexico. However, in the last decade this crop averaged yields as low as 0.7 tons per hectare. Therefore, the purpose of this study was to test if soil solarization is a suitable pre-planting soil treatment to improve growth, nutrition and yield of beans in northeast Mexico. Five different periods of soil solarization were evaluated during the spring of 2008: 0, 30, 40, 50 and 60 days of soil solarization. Soil temperatures were recorded during soil solarization to estimate total heat units. After soil solarization bean seeds were sown in plastic-mulched rows and leaf area, potassium, calcium and magnesium concentration and yield were measured. Leaf area and concentrations of potassium, calcium and magnesium were increased by all treatments of soil solarization when compared with the non-solarized soil. Sixty days of soil solarization produced yields of 3.7 tons per hectare while no solarization produced yields of 2.1 tons per hectare. Soil heat units were positively correlated with yield, suggesting that the increase in yield is due to an increase in heat accumulation during soil solarization in addition to an increase of leaf area and to an enhancement of plant nutrition.

Can plant litter affect net primary production of a typical steppe in Inner Mongolia?

Question: Litter (dead leaves or stems) affects production by conserving soil moisture. However, that role is not clear for grasslands where most precipitation falls during the growing season when the demand for water is high. Our question was: Does litter affect forage production in such an environment? Location: Typical steppe, Inner Mongolia. Methods: We examined the role of plant litter in two experiments where litter was either removed or added in a protected or heavily grazed site, respectively, in autumn and in spring in a split plot design. The treatments (control, moderate and heavy litter application) were applied once in five replications but repeated at new locations in each of 3 years. This was done to examine only the direct effect of litter on annual net primary production and selected plant characteristics and not potential secondary effects. We also measured soil moisture and soil temperature. Results: Removing litter caused a reduction in the amount of grass (Leymus chinensis) that was produced, but litter addition caused an inconsistent effect among years, with moderate applications producing the most positive effects. Litter removal resulted in shorter and less dense plants of L. chinensis and Carex duriuscula, while heavy litter addition in autumn reduced plant height of both Cleistogenes squarrosa and C. duriuscula. Conclusions: Litter was effective for enhancing soil moisture status and reducing soil heat units in the typical steppe of Inner Mongolia. Therefore, litter mass may serve as an index of grassland health in such environments.

Interactive Effects of Landscape Position and Time of Application on the Response of Spring Wheat to Fall‐Banded Urea

The objective of this experiment was to quantify the effect of landscape position and time of application on the agronomic efficiency of fall‐banded urea [CO(NH2)2] for spring wheat (Triticum aestivum L.) grown in the eastern prairie region of Canada. Landscape positions in this experiment were defined as high and low based on their relative elevations to one another within the field. Fertilizer treatments included urea banded at three different times in the fall (early, mid‐, and late fall), in the spring at planting, plus a control with no fertilizer N added. In the low landscape positions, grain yield, total crop N uptake, grain yield increases (GYI), and crop nitrogen use efficiency (NUE) for fall‐banded urea (all relative to spring‐banded urea) increased linearly with delayed application dates and declining soil temperatures on date of application. However, only crop N uptake and NUE were related to cumulative soil heat units (SHU) from date of fertilizer application until freeze‐up, and no measure of crop response to N was related to cumulative nitrification heat units (NHU). In the high landscape positions, the performance of fall‐banded urea was not related to any measures of time and/or soil temperature. These results can be used to predict the increase in crop response to fall‐banded N as a result of delaying application in low areas of the landscape. Our study also shows that date of application and soil temperature are robust and practical indicators for determining the appropriate time to fall‐band urea fertilizer in these areas.

Transformation of Fall‐Banded Urea: Application Date, Landscape Position, and Fertilizer Additive Effects

A 2‐yr study was initiated in the fall of 2000 to generate fundamental information on the effects of application date, landscape position, and a combined urease and nitrification inhibitor (NBPT [N‐(n‐butyl) thiophosphoric triamide] and DCD [dicyandiamide], respectively) on the rate of transformation of fall‐banded urea fertilizer into NH4+ and eventually NO3− under conditions typical for Manitoba, Canada. Landscape position did not have a large effect on the conversion of banded urea to NO3− under the moisture conditions present during the autumn period at the sites. Delaying application of fall‐banded urea fertilizer into the late fall and the presence of NBPT and DCD slowed nitrification and increased the recovery of fertilizer N as NH4+ (%RFN as NH4+) in the soil before it froze. Date of application, the soil temperature on the date of application, and the accumulation of SHU (soil heat units) and NHU (nitrification heat units) were all linearly related to the %RFN as NH4+ Accumulated SHU and NHU were most strongly correlated with the %RFN as NH4+ at the end of the fall, with and without inhibitors. The interactions between time, temperature, and nitrification demonstrate that producers in the Northern Great Plains region must consider the overall length of time that fall‐applied N fertilizer will be exposed to the soil before the soil freezes, even after the soil temperature has reached a given level and even if the fertilizer is banded.

Cover crop effects on nitrogen mineralization and availability in conservation tillage cotton

Understanding cover crop influences on N availability is important for developing N management strategies in conservation tillage systems. Two cover crops, cereal rye (Secale cereale L.) and crimson clover (Trifolium incarnatum L.), were evaluated for effects on N availability to cotton (Gossypium hirsutum L.) in a Typic Kanhapludult soil at Watkinsville, Ga. Seed cotton yields following clover and rye were 882 kg ha−1 and 1,205 kg ha−1, respectively, in 1997 and were 1,561 kg ha−1 and 2,352 kg ha−1, respectively, in 1998. In 1997, cotton biomass, leaf area index, and N were greater on some dates following crimson clover than following rye but not in 1998. During 1997, net soil N mineralized increased with time in both systems, but a similar response was not observed in 1998. Net soil N mineralization rates following crimson clover and rye averaged, respectively, 0.58 kg and 0.34 kg N ha−1 day−1 in 1997 and 0.58 kg and 0.23 kg N ha−1 day−1 in 1998. Total soil N mineralized during the cotton growing season ranged from 60 kg ha−1 to 80 kg ha−1 following crimson clover and from 30 kg ha−1 to 50 kg ha−1 following rye. Soil N mineralization correlated positively with heat units and cumulative heat units. Net soil N mineralization rates were 0.023 kg ha−1 heat unit−1 once net mineralization began. Soil heat units appeared to be a useful tool for evaluating N mineralization potential. Nearly 40% of the rye and 60% of the clover biomass decomposed during the 6 weeks prior to cotton planting, with nearly 35 kg N ha−1 mineralized from clover.

Planting Time For Early‐Season Pearl Millet and Grain Sorghum in Nebraska

Pearl millet [Pennisetum glaucum (L.) R. Br.] is a potential crop for the Great Plains, but there are few studies on production practices. The research objective was to determine the optimal planting time for pearl millet in Nebraska relative to sorghum [Sorghum bicolor (L.) Moench]. This would optimize pearl millet yields, thus increasing the prospect for pearl millet as a crop. Studies were conducted on Sharpsburg silty clay loam (fine, smectitic, mesic, Typic Argiudoll) and Ortello sandy loam (coarse‐loamy, mixed, mesic, Udic Haplustoll) soils between 1995 and 2001. Optimal planting times were determined by relating yields with calendar date, cumulative air heat units, cumulative soil heat units, and soil temperatures. Relative yields related to air or soil heat units were effective in determining the optimal planting time. Optimum pearl millet planting times were 399 air heat units or 410 soil heat units after 1 April for the Sharpsburg soil and 406 soil heat units for the Ortello soil. The optimal sorghum planting time was 308 air heat units or 307 soil heat units after 1 April for the Sharpsburg soil and 402 air heat units after 1 April for the Ortello soil. Both crops had large planting time windows, allowing flexibility in planting time. Sorghum outyielded pearl millet for May and early‐to mid‐June planting times by 0.57 to 2.32 Mg ha−1 while pearl millet had higher yields by 0.95 to 1.20 Mg ha−1 for late June and July planting times. Sorghum produced greater yields than pearl millet for most planting times while pearl millet produced greater yields than sorghum for very late planting times.

Precision Planting for sh2 Sweet Corn Stand Establishment

The impact of soil type and planting depths on the emergence of three hybrids of shrunken 2 sweet corn with varying seed vigor was investigated. Two field trials were completed (planted on 18 Sept. 1996 and 6 May 1997) in a field containing Crosby and Kokomo soil types in Columbus, Ohio. Three sh2 hybrids (`Starship', `Skyline', and `Confection') were planted at 1.3-, 2.5-, and 5.1-cm depths with six replications on each of the two soils in the fall study. The same hybrids were planted the following spring with an adjustment to 2-, 4-, and 6-cm planting depths over the same soil types, and the addition of a transition soil. The use of data loggers in 1997 allowed for continual monitoring of soil temperatures at each of the planting depths throughout the field, and calculation of soil heat units throughout the emergence period. There were no significant differences between depths for average temperatures or soil heat units. Minimum temperatures were significantly colder on the lighter color soil and had a linear relationship with emergence counts. Soil tests were carried out at all sites for P, K, Mg, and Ca. Although significant differences were found with the Kokomo soil having higher nutrient levels than the transition or Crosby soil, levels throughout the field were more than adequate for emergence. Compaction and soil moisture measurements were taken with a neutron probe. Dry density was significantly higher on the lighter color soils, while soil moisture percentage climbed from 18% on Crosby to 25% on the Kokomo. In both years, there were significant differences in emergence indices based not only on hybrid and planting depth but also on location. Emergence ranged from below 50% to nearly 100% depending on the treatment and field location. Each of the 108 sampling points was located with a GPS receiver and the use of ArcView software allowed for data layers to be stored and mapped so that prescriptions could be made for best stand establishment.

Soil Moisture and Postdormancy Emergence of Colorado Potato Beetles (Coleoptera: Chrysomelidae): Descriptive Model and Field Emergence Patterns

Variation in postdiapause emergence patterns of Colorado potato beetle adults over six consecutive years at a single site was only partially explained by cumulative soil heat units. However, soil moisture measured at a depth of 15 cm and daily rainfall accounted for much of the unexplained variation in yearly emergence patterns. We hypothesized that emergence of overwintered beefles was a two-stage process consisting of thermally regulated postdiapause development followed by moisture-driven emergence from the soil. To test this hypothesis we constructed two simulation models that mirrored these processes. One model used soil moisture measured at a depth of 15 cm to drive emergence, while the other used daily rainfall for the same purpose. Both models were able to represent the field data; however, the best congruence was achieved when rain was an independent factor. Because rainfall was a better determinant of moisture, the dynamics of moisture at the soil surface may be of great importance to the beetle. Greater precision in model simulations could probably be achieved by improving the way in which soil moisture dynamics are depicted.

Soil water effects on the use of heat units to predict crop residue carbon and nitrogen mineralization

Soil heat units (degree days) have previously been shown to predict net N mineralization from crop residues and papermil sludge. The present study was designed to identity the effects of soil water potential on predictions of mineralization with heat units and to compare field and laboratory results of white lupin (Lupinus albus L. cv. ‘Ultra’) N mineralization. Lupin-amended soil and unamended controls were incubated at factorial combinations of temperature (15, 20, and 25°C) and soil moisture (-0.30,-0.03, and-0.01 MPa) for 198 days. Incorporation of the lupin residue resulted in net N immobilization. No net N mineralization had been observed for any temperature at a soil moisture level of-0.30 MPa by the close of the incubation study. The number of heat units that accumulated until commencement of net N mineralization did not differ for five of the six remaining temperature x water treatment combinations.The number of heat units that accumulated until net N mineralization began (2058–2814 degree-days) in the present study were similar to those reported in a complementary field study (1990–2360 degree-days). Temperature and moisture interactively affected lupin-residue C mineralization. The cumulative substrate C that had evolved by the time of net N mineralization did not differ for a given temperature between soil moisture levels of-0.03 and-0.01 MPa. Heat units were not useful for describing crop-residue C mineralization in this study. Heat units appear to adequately predict net N mineralization from organic residues at soil water potentials within the-0.03 to-0.01 MPa range, but may not be valid for prolonged drier conditions.

SEASONAL PATTERNS OF NITROGEN FIXATION AND DRY MATTER PRODUCTION BY CLOVERS GROWN IN THE PEACE RIVER REGION

Alsike clover (Trifolium hybridum L.) and red clover (T. pratense L.) were established in field plots on an Orthic Gray Luvisol (Hazelmere CL) and a Black Solod (Landry CL) in 3 consecutive yr, 1972, 1973 and 1974. Data were collected in the 2 yr following the year of establishment. The factors measured included seed and forage yield, dry matter production rate, potential nitrogenase activity (acetylene reduction), soil temperature, air temperature, soil moisture and NH+4-N and NO−3-N content of the soil. Based on calculations using the theoretical C2H2:N2 ratio of 3:1, alsike clover annually fixed 20.8–143.0 kg N/ha, and red clover fixed 15.3–77.3 kg N/ha on the Orthic Gray Luvisol. Also, alsike clover fixed more N2 earlier in the growing season than red clover. The estimate of annual N2(C2H2) fixation by both clovers on the Black Solod was less than one half that on the Orthic Gray Luvisol. There was little difference between the N2(C2H2) fixation by clover crops harvested for forage and those used for seed production. However, the amount of N2(C2H2) fixed always equalled or exceeded the amount of nitrogen removed in the seed, but only occasionally exceeded the amount removed in the forage. Yield and N2(C2H2) fixation varied widely among years, suggesting considerable climatic influence. However, the measured climatic and soil factors were not consistently correlated with potential nitrogenase activity. The seasonal pattern of potential nitrogenase activity appeared to be influenced by the phenological development of the plant. Activity commenced early in May, increased to a maximum about mid-June (flower initiation), and then decreased and generally remained low for the remainder of the growing season. Significant deviations from the usual seasonal profile of potential nitrogenase activity occurred in years with periods of moisture stress or with above average precipitation and soil heat units.