F. Selles

Quantifying short-term effects of crop rotations on soil organic carbon in southwestern Saskatchewan

Crop management practices can have a major influence on soil fertility and soil organic C (SOC) sequestration. We need to accurately measure and estimate changes in SOC in the short term (<20 yr). A 10-yr crop rotation experiment, conducted on a medium-textured Orthic Brown Chernozem at Swift Current, in southwestern Saskatchewan, was sampled in 1990 (3 yr after initiation of the study) and in 1993 and 1996, to measure SOC changes under nine crop rotation treatments. Minimum tillage practices were used. The stubble was cut high to enhance snow trap and N and P fertilizer applied based on soil tests. Grain and straw yields of the cereals, and hay yields of the crested wheatgrass (CWG) [Agropyron cristatum (L.) Gaeertn.] were measured annually. An empirical equation which uses two simultaneous first order kinetic expressions, one to estimate crop residue decomposition and the other to estimate soil humus C mineralization was used, together with crop residue (straw and estimated root) C inputs, to estimate S...

Distribution of phosphorus fractions in a Brazilian Oxisol under different tillage systems

Abstract Changes in residue management resulting from adoption of conservation tillage systems have the potential to alter the concentration and distribution of phosphorus (P) in the soil surface. The objective of this study was to determine the effect of methods of tillage management on the distribution and concentration of organic and inorganic forms of soil P near the soil surface (0–10 cm depth) for an Oxisol in southern Brazil. The tillage systems included zero tillage (ZT) (seeding directly onto the standing stubble of the previous crop), minimum tillage (MT) (seeding the crop after chisel plowing to 15-cm depth and disk harrowing to 7.5 cm), or conventional tillage (CT) (seeding after disk plowing to 20-cm depth with nearly total soil inversion plus two disk harrowings to 10-cm depth). After a period of five years, reducing tillage through adoption of MT or ZT practices increased total P in the surface 10 cm by 15% when compared to CT. Although there were no differences in amounts of total P between MT and ZT systems, under ZT management larger amounts of labile organic and inorganic forms of P accumulated close to the soil surface, followed by a reduction below the 6-cm depth. Under MT, the labile organic and inorganic forms of P were uniformly distributed within the surface 10 cm of soil. The accumulation of high levels of labile P near the soil surface under ZT followed a distribution pattern similar to the accumulation of organic residues in the soil. This would help explain why other workers have found increased P uptake by crops grown under ZT, and why more available P can be extracted by common soil testing methods from the surface 7 to 10 cm of soils under ZT than under CT management.

Adopting zero tillage management: Impact on soil C and N under long-term crop rotations in a thin Black Chernozem

Society’s desire to sequester C in soils, thereby reducing the net loss of CO2 (a greenhouse gas) to the atmosphere, is well known. It is also accepted that the choice of appropriate agricultural management practices adopted by producers will affect this goal. However, quantification of the extent and rate at which it can be achieved is uncertain. A crop rotation experiment that was initiated in 1957 on a thin Black chernozemic clay soil at Indian Head, Saskatchewan, was managed using conventional tillage until changed to zero tillage in 1990. Soil was sampled (0- to 7.5- and 7.5- to 15-cm depths) in May 1987 and 1997 to determine the effects of treatments on soil organic C (SOC) and total N. The rotations were: fallow-wheat (Triticum aestivum L.) (F-W), F-W-W, continuous wheat (Cont W), legume green manure (GM)-W-W, and F-W-W-hay (legume-grass)-hay-hay (F-W-W-H-H-H). The monoculture cereal rotations were either fertilized with N and P based on soil tests or unfertilized, while the legume systems were bot...

Tillage and crop rotation effects on soil organic C and N in a coarse-textured Typic Haploboroll in southwestern Saskatchewan

An 11 year study conducted in the semiarid prairie of southwestern Saskatchewan, Canada, to determine the influence of fallow frequency and tillage on yields and economics of durum wheat (Triticum turgidum L.) production, was used to assess changes in soil organic C and N. The soil was a coarse-textured, Typic Haploboroll. Cropping frequency (fallow-wheat vs. continuous wheat) had no effect on organic C or N concentrations or amount in this study. Compared with conventional mechanical or minimum tillage, no-tillage increased organic C and N concentrations in the 0–7.5 cm soil depth during the final 4 years of the experiment when crop yields and residue production were above average. However, there was no effect of tillage on C or N concentration in the 7.5–15 cm depth, nor on the mass of organic C or N in either depth. The amount of organic C in the top 15 cm of soil increased by 1.6 t ha−1 over the 11 year period (average for all systems). Most of this increase occurred in the final 4 years and was generally related to the amount of crop residues returned to the soil. Because neither rotation nor tillage influenced crop production, these practices did not affect organic C or N. We concluded that there was limited opportunity to sequester additional C in coarse-textured soils located in semiarid climates if monoculture cereal systems are used under conventional (mechanical) or no-tillage.

Tillage - fertilizer changes: Effect on some soil quality attributes under long-term crop rotations in a thin Black Chernozem

A crop rotation experiment initiated in 1958 on a thin Black Chernozemic clay at Indian Head, Saskatchewan, was managed using conventional tillage until 1989 and changed to zero-tillage in 1990. We soil sampled in 1987 and 1997 to determine management effects on selected soil biochemical characteristics, and the change in some of the more labile soil quality attributes relative to the change in soil organic C and total N. Rotations examined were: fallow-wheat (Triticum aestivum L.) (F-W), fallow-wheat-wheat (F-W-W), continuous wheat (Cont W), legume green manure (GM)-W-W, and F-W-W-hay (legume-grass)-hay-hay (F-W-W-H-H-H). The monoculture cereal rotations were either fertilized with N and P based on soil tests or unfertilized, while the legume-containing systems were unfertilized. There was also a F-W-W (N + P) treatment, in which about 20% of the straw was harvested each crop year. With the change to zero-tillage management in 1990 and in anticipation of greater soil water storage, higher rates of N were...

Long-term assessment of management of an annual legume green manure crop for fallow replacement in the Brown soil zone

In the Brown soil zone of western Canada summerfallowing (F) is traditionally used to reduce the water deficit associated with cereal production, but frequent use of this practice results in soil degradation and reduces the N-supplying capacity of soils. Some scientists suggest that an annual legume green manure crop (LGM) could be used as a partial-fallow replacement to protect the soil against erosion and increase its N fertility, particularly when combined with a snow-trapping technique to replenish soil water used by the legume. We assessed this possibility by comparing yields, N economy, water use efficiency, and economic returns for hard red spring wheat (W) (Triticum aestivum L.) grown in rotation with Indianhead black lentil (Lens culinaris Medikus) green manure (i.e., LGM-W-W) vs. that obtained in a traditional F-W-W system. Further, we assessed whether a change in manage ment of the LGM crop (i.e., moving to earlier seeding and earlier turn-down) was advantageous to the overall performance of th...

Effect of 6 years of zero tillage and N fertilizer management on changes in soil quality of an orthic Brown Chernozem in Southwestern Saskatchewan

Abstract In the Brown soil zone of Saskatchewan, limited moisture poses the greatest hindrance to crop production; consequently, the predominant cropping system used by producers is a spring wheat ( Triticum aestivum L.)-fallow rotation. In the fallow period, weeds are controlled primirily by tillage which results in severe erosion and soil degradation. Producers might overcome their economic and environmental problems by using cereal trap strips prepared at harvest to retain snow and increase moisture conservation, especially if this is coupled with zero-tillage continuous cropping and proper fertilizer management. A 6-year experiment in which the latter practices were investigated was sampled and analysed for various soil physical, biochemical and biological properties and these measurements compared with similar ones made on the adjacent area that had been in conventionally tilled fallow-wheat for more than 70 years. Results showed that the zero-till continuous wheat system has increased total organic matter, microbial biomass N, amino compounds, C and N mineralization and phosphatase activity in the top 7.5 cm of soil, but in most cases there was little change in the 7.5–15-cm depth. Bulk density was not affected by tillage or by cropping but soil aggregation was increased by a single year of cropping (compared with tilled fallow).

Long-term effect of cropping system and nitrogen and phosphorus fertilizer on production and nitrogen economy of grain crops in a Brown Chernozem

Assessment of the long-term impact of fertilizers and other management factors on crop production and environmental sustainability of cropping systems in the semi-arid Canadian prairies is needed. This paper discusses the long-term influence of N and P fertilizers on crop production, N uptake and water use of hard red spring wheat (Triticum aestivum L.), and the effect of the preceding crop type [flax (Linum usitatissimum L.) and fall rye (Secale cereale L.)] on wheat grown on a medium-textured, Orthic Brown Chernozem at Swift Current, Saskatchewan. We analysed 36 yr of results (1967–2002) from eight crop rotation-fertility treatments: viz., fallow-wheat receiving N and P (F-W, N + P), three F-W-W treatments fertilized with (i) N + P, (ii) P only, and (iii) N only; two other 3-yr mixed rotations with N + P (i) F-flax-W (F-Flx-W) and (ii) F-fall rye-W (F-Rye-W); and two continuous wheat rotations (Cont W), one receiving N + P and the other only P. Growing season weather conditions during the 36-yr period w...

Effect of crop management on C and N in long-term crop rotations after adopting no-tillage management: Comparison of soil sampling strategies

Society is interested in increasing C storage in soil to reduce CO2 concentration in the atmosphere, because the latter may contribute to global warming. Further, there is considerable interest in the use of straw for industrial purposes. Using soil samples taken from the 0- to 7.5-cm and 7.5- to 15-cm depths in May 1987 and September 1996, we determined organic C and total N in five crop rotations (nine treatments) using automated Carlo Erba combustion analyzer. The experiment was managed using conventional mechanical tillage from 1957 to 1989; it was changed to no-tillage management in 1990. Our objective was to determine: (a) if change to no-tillage management had changed soil C and N storage, and (b) if method of calculating organic C and N change would influence interpretation of the results. All three methods of calculation confirmed the efficacy of employing best management practices (e.g., fertilization based on soil tests, reducing summerfallow, including legumes in rotations) for increasing or m...

REGRESSION MODEL FOR PREDICTING YIELD OF HARD RED SPRING WHEAT GROWN ON STUBBLE IN THE SEMIARID PRAIRIE

Soil testing laboratories require predictive equations to make accurate fertilizer recommendations to cereal producers in the Canadian prairies. We used results from two 12-yr experiments (one studying snow management × fertilizer rates, and the other a tillage experiment), conducted on a medium-textured Orthic Brown Chernozem at Swift Current, Saskatchewan, to develop a regression model to estimate grain yield of hard red spring wheat (Triticum aestivum L.) grown on stubble. Stepwise regression, with backward elimination, was used to develop the relationship:Y = 1006 + 10.53 WU − 0.017 WU2 + 5.52 FN − 0.095 FN2 − 33.16 SN + 0.436 SN2 − (0.112 FN × SN) + (0.057 FN × WU) + (0.159 SN × WU) − 1.26 DD (R2 = 0.89, P = 0.001, n = 262)where Y = grain yield (kg ha−1), WU = estimated water use (mm), SN = soil test N (kg ha−1), FN = rate of fertilizer N (kg ha−1), and DD = degree days >5 °C (°C-days). Water use was available spring water in the 0- to 1.2-m depth plus 1 May to 31 July precipitation + irrigation, and...