P. E. Rasmussen

Long-Term Impacts Of Tillage, Fertilizer, And Crop Residue On Soil Organic Matter In Temperate Semiarid Regions

Publisher Summary This chapter reviews past progress toward enhancing the level and quality of organic matter in soil. Annual cropping replaced fallow in many areas, which has reduced organic matter loss from soil. Greater fertilizer use and varietal improvement increased cereal grain yield and straw production, which raised the level of C return to the soil. Carbon input has shown to have a significant impact on the organic matter level. Stubble-mulch and no-till systems conserved up to 2% more organic matter per year in surface soil than plowing. Crop rotation, green manuring, and reduced tillage practices have lost some of their glamour with the advent of chemical fertilizers and pesticides, and many of the long-term experiments have been discarded for more pressing research. Fertilizer and tillage research has expanded, and crop improvement has received new impetus. Less reliance on crop rotation and green manure has beenpartially responsible for increasing use of inorganic fertilizer. Soil erosion tends to increase with less crop rotation and greater reliance on mechanical tillage and clean fallow.

Soil C and N changes under tillage and cropping systems in semi-arid Pacific Northwest agriculture

Soils in semi-arid regions are highly susceptible to soil organic matter (SOM) loss when cultivated because of erratic yield, removal of crop residue for feed or fuel, uncontrolled soil erosion, and frequent fallowing to increase water storage. It is important to quantify the effect of each factor to be able to identify agoecosystems that are sustainable and recognize the management practices that best sequester C in soil. We identified changes in SOM in long-term experiments, some dating from the early 1900s, by evaluating tillage and crop rotation effects at several locations in semi-arid regions of the US Pacific Northwest. The major factors influencing changes in organic C and N were the frequency of summer-fallow and the amount of C input by crop residue. Soil erosion was low in long-term studies, but even limited soil loss can have a substantial impact on C and N levels if allowed over many years. Yearly crop production is recommended because any cropping system that included summer-fallow lost SOM over time without large applications of manure. We conclude that most of the SOM loss was due to high biological oxidation and absence of C input during the fallow year rather than resulting from erosion. Decreasing tillage intensity reduced SOM loss, but the effect was not as dramatic as eliminating summer-fallow. Crop management practices such as N fertilization increased residue production and improved C and N levels in soil. SOM can be maintained or increased in most semi-arid soils if they are cropped every year, crop residues are returned to soil, and erosion is kept to a minimum. SOM loss may be more intense in the Pacific Northwest because fallowing keeps the soil moist during the summer months when it would normally be dry. Our experiments identify two primary deficiencies of long-term studies to measure C sequestering capability: (1) soil C loss can be partitioned between erosion and biological oxidation only by estimation, and (2) C changes occurring below 30 cm in grassland soils cannot be quantified in many instances because samples were not collected.

Diseases of wheat in long-term agronomic experiments at Pendleton, Oregon

Diseases of winter wheat were evaluated over 3 years in four long-term (27- to 60-year) cropping system experiments. Disease incidence and severity were evaluated with respect to seasonal precipitation and soil chemical and microbiological parameters. Take-all and eyespot were associated with increasing precipitation, and Rhizoctonia root rot and Fusarium crown rot were favored by drought. Eyespot and crown rot increased with rate of applied nitrogen and were inversely proportional to soil pH. Surface residue from previous crops had variable effects on diseases. Crown rot increased with amount of surface residue and was directly correlated with soil organic nitrogen and carbon. Surface residue also had a variable effect on Rhizoctonia root rot, depending on the magnitude of soil microbial respiration; root rot increased directly with amount of residue in a wheat-summer fallow rotation and was unaffected by residue or tillage in a wheat-pea rotation. Repeated burning of wheat stubble caused variable disease response, depending on precipitation and nitrogen rate. At high fertility, burning suppressed Pythium root rot and Rhizoctonia root rot, and enhanced eyespot and take-all. Effects of crop rotations on diseases appeared related to soil microflora effects on pathogen survival or virulence. Rhizoctonia root rot was most damaging in wheat-fallow rotation, Pythium root rot in wheat-fallow and annual wheat, and eyespot and crown rot in annual wheat. Diseases were collectively least prevalent where nitrogen in a wheat-fallow rotation was applied as pea vines or manure, rather than as inorganic fertilizer. Diseases also were generally less damaging in a wheat-pea rotation than in an annual wheat or wheat-fallow rotation. Soilborne plant pathogenic fungi appeared to suppress wheat yield by 3 to 12%. Long-term experiments provided insights to crop management and seasonal effects that are unlikely to be identified in short-term experiments.

Tissue analyses guidelines for diagnosing sulfur deficiency in white wheat

SummaryVisual identification of S deficiency in white wheat is difficult since deficiency symptoms are nearly identical with those of N deficiency. In this study, S deficiency was best identified by determining the total N/S ratio rather than S concentration in vegetative tissue. Vegetative growth generally decreased from tillering to boot when the whole plant N/S ratio exceeded 17. The N/S ratio in S-sufficient plants declined gradually with age, implying that the critical N/S ratio may decline with advancing growth. Changes in stem: leaf ratio could have been responsible for the decline since the N/S ratio in stem tissue at heading was less than that of green leaf tissue.Sulphur concentration less reliably indicated S-deficiency, because differences in S levels between S-deficient and S-sufficient wheat, were often less than year-to-year variation of S concentration of plants sampled at the same growth stage. In addition, S concentration in whole plants declined sharply between tillering and heading. These factors make it difficult to designate a critical S level. Sulfur distribution among various plant organs suggests that critical S levels might best be obtained by utilizing green leaf tissue.Nitrogen concentration in S-sufficient wheat plants also decreased quite rapidly with growth, which indicates a similar difficulty for determining critical N percentages. Consequently, the most reliable distinction between N and S deficiency in wheat was accomplished by evaluation of the total N/S ratio in whole plant tissue.

Effects of fertilizer and stubble burning on downy brome competition in winter wheat

Abstract Increased downy brome (Bromus tectorum) infestation is one of the dominant impediments to adoption of conservation tillage. Surface residues often increase grassy weed competition and lower the yield of cereal crops. Crop residue and fertilizer placement effects on downy brome growth and nutrient uptake in relation to that of winter wheat (Triticum aestivum L.) were conducted in two separate years; one involving conventional (plow) tillage and the other no‐till. Crop residue (burning versus no burning) and fertilizer placement (broadcasting versus subsurface banding) differentials were present both years. The conventional‐till study also included nitrogen (N) rates from 0 to 168 kg/ha and an N only versus nitrogen+phosphorus+sulfur (N+P+S) comparison. Burning increased early‐spring wheat growth substantially, with only limited effect on downy brome population or growth. Broadcasting of fertilizer increased downy brome density and growth compared to banding. Wheat, in contrast, had greater growth ...

Management of grain stubble for conservation-tillage systems

Abstract Standing wheat stubble decreased seed-level soil temperature and mid-canopy photosynthetically-active radiation compared with burned plots. Plants within standing stubble had reduced main-stem leaf development, drastically reduced tillering and above-ground dry weights at late tillering, and had shorter stems at harvest. Because growing conditions from anthesis to maturity were highly favorable, depressed plant development and growth caused by standing stubble decreased grain and straw yield only slightly.

Fertility management in dryland conservation cropping systems of the Pacific Northwest

The Pacific Northwest dryland region is moving toward conservation tillage to control excessive erosion on steep slopes, but progress has been slow because of adverse effects on plant growth and yield. Fertility relations in cereal grains with conventional tillage are well known, with deficiencies occurring for nitrogen, sulfur, and phosphorus, in declining order of frequency. N and S deficiencies are more severe in conservation tillage, although the pattern of crop response to nutrient application is the same as in conventional tillage. Placing nutrients in a subs urface band near the seed is more effective than broadcasting on the surface. Higher fertility is required near developing root systems to offset greater competition from grassy weeds and more intense pressure from root-pruning soil pathogens. Conservation tillage alters soil fertility and plant growth in different ways on different landscapes. These differences must be considered to ensure tha t conservation tillage will be effective over the entire field.

Effect of nitrogen, sulfur, and phosphorus sufficiency on nutrient content in white winter wheat

Abstract Correct interpretation of nitrogen (N), sulfur (S), and phosphorus (P) deficiencies in white winter wheat grown in soil is difficult because of similarity of visual symptoms and rapidly‐changing nutrient content after tillering. We collected plant samples at late tillering and harvest from white winter wheat grown under three tillage systems and six fertility regimes to evaluate yield response, nutrient concentration, and DRIS index values. Tillage included no‐till annual crop, conventional‐till annual crop, and conventional‐till wheat after fallow. Fertility regimes were: None, Moderate N, Moderate N+S, High N+S, Moderate N+S+P, and High N+S+P. Nitrogen and P increased grain yield under all tillage systems and S in annual crop systems. Plant nutrient concentration and nutrient ratios at tillering were only moderately successful in identifying nutrient deficiency. Nitrogen and S deficiency tended to intensify between late‐tillering and harvest, but P deficiency did not. Both N and S deficiency we...

Surface residue and nitrogen fertilization effects on no-till wheat

Surface residue helps to reduce soil erosion, but wheat (Triticum aestivum L.) yield in conservation tillage is often less than in conventional tillage, especially when a cereal follows a cereal. Plant development was delayed and tiller initiation less consistent in no-till (NT) winter wheat than in conventionally-tilled (CT) wheat grown following spring wheat. Flattening of the straw rather than leaving it standing improved plant development and grain yield. Burning of straw in NT improved tiller initiation and increased yield. Plants responded to nitrogen (N) similarly in both systems. Lower yield in NT appeared primarily due to poorer tiller initiation and lower tiller survival. To achieve equality with CT, ways must be found to eliminate plant stress during early-tiller initiation.

Long-term Residue Management Experiment: Pendleton, Oregon USA

The Residue Management experiment is one of six long-term studies maintained by the Columbia Basin Agricultural Research Center, Oregon State University Agricultural Experiment Station. The Center is located 15 km northeast of Pendleton, Oregon at 45° 44′ north and 118° 37′ west. It lies within the Columbia Plateau physiographic province between the Cascade and Rocky mountains. The climate is semi-arid, but partially influenced by maritime winds from the Pacific Ocean. Winters are cool and wet, the summers hot and dry. Precipitation occurs primarily during the winter. Annual precipitation is 420 mm, with 70% received between 1 September and 31 March. Winter precipitation falls mainly as rain, with limited duration of snow cover in most years. Average annual temperature is 10.2 °C, but ranges from -0.6 °C in January to 21.2 °C in July. Weather is measured daily 200 m from the site. Temperature and precipitation have been recorded since 1931, 10-cm soil temperature since 1962, wind speed and water evaporation since 1963, and solar radiation and humidity since 1982. Elevation is 455 m above sea level. Soils consist of loess from Pleistocene alluvial deposits overlying basalt flows of Miocene age. They are classified as coarse silty mixed mesic Typic Haploxerolls by the USDA classification system. Soils are well drained and depth to water table is greater than 50 m. Soil depth ranges from 1 to 2 m, depending upon landscape position. Soil texture is silt loam throughout the profile. The upper 30 cm of soil contains 18% clay, 70%) silt, and 12% fine sand. The area was originally a mid-grass prairie that was first cultivated in about 1885.