ALBERT

Beschreibung: The effects of crop rotations and various cultural practices on soil organic matter quantity and quality in a Rego, Black Chernozem with a thin A horizon were determined in a long-term study at Indian Head, Saskatchewan. Variables examined included: fertilization, cropping frequency, green manuring, and inclusion of grass-legume hay crop in predominantly spring wheat (Triticum aestivum L.) production systems. Generally, fertilizer increased soil organic C and microbial biomass in continuous wheat cropping but not in fallow-wheat or fallow-wheat-wheat rotations. Soil organic C, C mineralization (respiration) and microbial biomass C and N increased (especially in the 7.5- to 15-cm depth) with increasing frequency of cropping and with the inclusion of legumes as green manure or hay crop in the rotation. The influence of treatments on soil microbial biomass C (BC) was less pronounced than on microbial biomass N. Carbon mineralization was a good index for delineating treatment effects. Analysis of the microbial biomass C/N ratio indicated that the microbial suite may have been modified by the treatments that increased soil organic matter significantly. The treatments had no effect on specific respiratory activity (CO2-C/BC). However, it appeared that the microbial activity, in terms of respiration, was greater for systems with smaller microbial biomass. Changes in amount and quality of the soil organic matter were associated with estimated amount and C and N content of plant residues returned to the soil. Key words: Specific respiratory activity, crop residues, soil quality, crop rotations

Beschreibung: Inorganic phosphorus (P) is generally believed to be relatively immobile in Chernozemic soils. However, available P (e.g., Olsen-P) has been found at depth in some soils and this has been postulated to be either the result of leaching or of transportation by plant roots. Lagumes, in particular, are believed to be involved in the latter mechanism. A long-term (34-yr) crop rotation study conducted on a heavy clay, thin Black Chernozemic soil at Indian Head, Saskatchewan, was sampled to a depth of 4.5 m in May and September 1991, to determine the influence of fertilization, cropping frequency, legume green manure and legume-grass hay crops on Olsen-P distribution in the soil profile. The results indicated that Olsen-P may indeed leach in Chernozemic soils, especially when fallow-containing cropping systems are fertilized. It also appeared that deep-rooted legumes, such as sweetclover Melilotus officinalis L.) green manure and alfalfa-bromegrass (Medicago sativa L. — Bromus inermis Leyss) hay crops do increase Olsen-P in the subsoil, possibly through root decomposition in situ. Key words: Rotations, bicarbonate-soluble Pi, legumes, green manure, fertilizers

Beschreibung: In pursuit of identifying sustainable agricultural production practices, there is an urgent need to develop or identify parameters that effectively describe and differentiate changes in the quality and quantity of soil organic matter resulting from crop management or cultural practices. The effectiveness of the potentially mineralizable nitrogen (No) concept for this purpose was examined using data from a 30-yr crop rotation study, carried out on a Rego thin Black Chernozem at Indian Head, Saskatchewan. Although Kjeldahl N and hydrolyzable soil amino-N are effective for demonstrating the beneficial influence of fertilizers, legumes and continuous cropping on total soil organic N content, they are less effective in identifying changes in organic matter quality. We have shown that a parameter which we called the "initial potential rate of N mineralization" [potentially mineralizable N (No) × rate constant (k) at time = 0] was effective in distinguishing both the absolute and qualitative changes in soil organic N due to various cultural and management practices. The results showed that fertilizers can be as effective as legumes, used either for green manure or for hay, in increasing the quantity and improving the quality of soil organic matter. A 6-yr rotation including 1 yr of fallow, 2 yr of spring wheat (Triticum aestivum L.) and 3 yr of bromegrass (Bromus inermis Leyss) and alfalfa (Medicago sativa L.) hay had a greater quantity and improved quality of soil organic N relative to that of unfertilized continuous wheat (Cont W), but they were equivalent to that of fertilized Cont W. Key words: Soil quality, potential mineralizable N, crop rotations, legumes, fertilizer effects

Beschreibung: Saskatchewan producers growing primarily spring-seeded cereals may be interested in diversifying their cropping alternatives. Winter wheat (Triticum aestivum L.) could provide one possible option, but its management could cause conflict with the busy fall and early spring activities for spring-seeded crops. A study was conducted at five sites (Swift Current, 4 yr; Melfort, 4 yr; and Scott, Lashburn, and Loon Lake, 1 yr each) in four soil zones (Brown, Dark Brown, and Black Chernozems and Gray Luvisol). The effect of time of application of N (seeding to early spring), source of N (ammonium nitrate vs. urea), and method of application (broadcast, midrow band, and seed-placed) on yield and grain protein concentration were investigated. The results varied with site and year (weather). Time of N application only influenced yields at Swift Current (Brown soil) where application on cool unfrozen soil in mid-October was as good as application in early spring and better than at other times, and application onto frozen, snow-covered soil in December was least effective. At Swift Current and Melfort, grain protein concentration did not respond to time of application; however, at Scott, Lashburn and Loon Lake, protein was highest for spring-applied N, followed by mid-October, and lowest when N was applied on frozen snow-covered soil. The effect of N source rarely affected grain yield or protein and was dependent on site and method of placement. The dangers of seed-placing N, especially urea, on overwinter survival and yields were evident in 2 yr at Swift Current. There was rarely any difference in yield or grain protein concentration when N was banded or broadcast at seeding time. Taking into account convenience of operation, the most opportune time for Saskatchewan producers involved in growing both spring and winter wheat to apply N would be mid-October in the Brown soil zone. In the other soil zones, early spring would be best. Broadcasting the N was the most appropriate method of application at all sites. Urea would be chosen over ammonium nitrate because there was little advantage of one source over the other and urea is generally cheaper. Key words: Urea, ammonium nitrate, protein, grain yields, plant population

Beschreibung: The impact of cultural practices on soil aggregate characteristics which determine the susceptibility of the soil to wind and water erosion was studied at two long-term (〉 30-yr) crop rotation sites on Black Chernozemic soils at Indian Head and Melfort, Saskatchewan. Surface soil (top 5 cm) taken in spring and fall, 1991, was air-dried and sieved by rotary sieve to measure aggregate size distribution. The water-stability of soil aggregates (1–2 mm) was determined after: (i) slow wetting, and (ii) fast wetting. Both rotation studies employed conventional tillage management until 1990 when the Indian Head experiment was converted to zero-tillage. Summerfallowing increased the wind-erodible (

Beschreibung: Water and N fertility are major limitations to cereal production in southwestern Saskatchewan. Both factors interact to determine grain yield and thus water use efficiency. A 9-yr study to assess the effects of snow management and fertilizer N on yields of spring wheat (Triticum aestivum L.) grown annually under zero-tillage provided an opportunity to quantify water use efficiency and relate this to apparent water used by the crop (WU), years of cropping (Yr) assumed to be 10 or fewer, soil test N (SN), and rate of fertilizer N (FN). The results showed that the estimated initial yield point (IYP) (available water required to produce the first unit of grain) and the yield increase per unit of water used beyond IYP increased with available N. Within the range of available N encountered in this study, IYP ranged between 60 and about 100 mm, values similar to those reported in the literature. However, because IYP is obtained by extrapolation, these values are regarded as first approximations. The yield increase per unit of WU increased with FN, varying between 10 and 14.4 kg ha−1 mm−1 (avg. 12.7) when a simple linear regression model was used to relate yield to WU. When a more accurate multiple regression equation that related yield to WU, SN, FN, and time and placement of fertilizer N was used, the marginal increase in yield per unit increase in available water (∂y/∂WU) ranged between 5 and 23 kg ha−1 mm−1 for assumed combinations of SN ranging between 0 and 50 kg ha−1 and FN ranging between 0 and 100 kg ha−1. The multiple regression model is superior to linear models because it allows the separation of available soil and fertilizer N effects. Key words: Water use efficiency, initial yield point, regression, N fertilizer, soil N

Beschreibung: In the Canadian prairie, producers generally sample soils in the autumn for nutrient analyses, whereas calibration of crop responses has been made based on soils sampled in the spring prior to seeding. A recent report suggests that available phosphorus (P) in soil increases between autumn and spring. At Swift Current, Saskatchewan, we have monitored bicarbonate-extractable P (Olsen P) every autumn and spring for the past 24 years, in four cropping systems: continuous wheat (Cont W), fallow-wheat (F-W), and two fallow-wheat-wheat (F-W-W) rotations. The first three systems received nitrogen (N) and P each crop year, with one F-W-W rotation receiving only N. These data were analyzed to test the authenticity of the aforementioned observations. We found that although there were some apparent overwinter increases in Olsen P there were also some decreases. Further, because of the considerable variability in Olsen P, relatively few of the overwinter changes were significant (P = 0.10). Efforts to correlate the changes in Olsen P to overwinter temperature or precipitation were unsuccessful. We concluded that Saskatchewan soil testing laboratories need not make adjustments to P fertilizer recommendations to account for changes in overwinter soil test P levels. Key words: Soil testing, bicarbonate-extractable P, crop rotations, available P

Beschreibung: Producers in western Canada have applied phosphorus (P) fertilizer to annual crops for many years. This has increased soil available P and gradually decreased the expected yield response to P fertilization, but yield responses to small amounts of P placed with the seed are still reported regardless of soil available P levels. Controlled growth chamber studies suggest that the P responses should be most apparent during cool, wet springs. This 24-yr field study compared the yields of two fallow–spring wheat–spring wheat (F–W–W) systems, one fertilized with N and P each crop year, and the other fertilized with only N. The study, which was part of a long-term crop rotation experiment, was conducted on an Orthic Brown Chernozemic loam at Swift Current, Saskatchewan. Bicarbonate-extractable P (Olsen P) in the 0- to 15-cm depth in spring of the treatment receiving no P remained relatively constant (about 19 kg ha−1) throughout the study, while P fertilizer application at 6.5 kg ha−1 yr−1 increased extractable soil P by about 0.9 kg ha−1 yr−1. However, this increase in available P has not reduced yield responses to seed-placed P over the years. Regression analysis showed that yield response to P on fallow soil was positively related to temperature between emergence and the three-leaf stage and to precipitation at dough stage, but negatively related to precipitation near seeding time. For wheat grown on stubble, response to P was negatively related to temperature between 10 and 16 June (i.e., about the three- to four-leaf stage) and positively to precipitation received at anthesis stage. We concluded that, although available P in prairie soils has probably increased in recent years, producers can still expect to receive a 10% yield increase when small amounts of P are applied with the seed.Key words: Crop rotations, bicarbonate-extractable P, Olsen P, temperature effects, effect of precipitation

Beschreibung: Numerous researchers estimate and report laboratory-determined lower limit of available water contents using −1.5 MPa water potentials. For medium-textured soils, laboratory-measured lower limits should be determined at potentials of at least −4 MPa, and possibly −10 MPa, when using pressure membrane procedures. However, because the lower limit of available water is dependent upon environmental, plant and soil factors, we agree with Ratliff et al. (1983) that field-measured lower limits are preferable to laboratory-measured lower limits. Field-measured lower limits of available water did not vary markedly between spring wheat, alfalfa and grass. Key words: Lower limit of available water, wheat, alfalfa, grass

Beschreibung: Results of fertilizer trials conducted throughout southwestern Saskatchewan were used to develop a production function relating grain yield increases of stubble-seeded spring wheat (Triticum aestivum L.) to available water, soil NO3-N content to 60 cm depth, soil PO4-P content to 15 cm depth, and fertilizer N and P applications. The trials were carried out from 1967 to 1971 and from 1978 to 1983 on mid-textured Brown Chernozemic soils. The model accounted for 67% of the variability in yield increases, and identified water availability as the single most limiting production factor, which by itself accounted for 15% of the variability in yield increases. Further, the effects of soil and fertilizer N and P were only significant in their interaction with water. Response to N fertilization was adequately described by a second-degree polynomial. The rates of fertilizer N required for maximum economic yield increases were related to the availability of soil NO3-N and PO4-P and to the rate of fertilizer P application, and inversely proportional to available water and the ratio of N cost to wheat price. The model indicated that soil NO3-N was equally effective as fertilizer N in raising yields, but considered soil PO4-P only one-fifth as effective as seed-placed fertilizer P in modifying the rates of fertilizer N required for maximum return. The effect of fertilizer P in the model was only significant in interactions with fertilizer N and soil PO4-P. Water use efficiency was proportional to the availability of soil and fertilizer nutrients. Key words: Fertilizer N, fertilizer P, soil testing, moisture use, soil N, soil P