Water use in a modified summer fallow system on semiarid northern Great Plains

Wheat (Triticum aestivum L.) is the major crop on semiarid northern Great Plains of the USA. Attempts to introduce alternate crops have had limited success. Alternate fallow-spring wheat rotation is the most common cultural practice. Our objective was to investigate water use and water use efficiency and suitability of alternative crops in semiarid northern Great Plains agricultural environment. The study was on glacial till Williams loam (fine-loamy mixed, Typic Argiboroll) 11 km north of Culbertson, MT. Plots, replicated four times in randomized blocks, were 12 m x 15 m. Rotations were: (1) fallow, sunflower (Helianthus annuus L.), barley (Hordeum vulgare L), winter wheat; (2) fallow, safflower (Carthamus tinctorious L.), barley, winter wheat; (3) fallow, buckwheat (Fagopyrum esculentum Moench.), annual legume/grain forage crop, spring wheat; (4) fallow, buckwheat, annual legume/grain forage crop, winter wheat; (5) fallow, spring wheat; (6) continuous spring wheat. Soil water to 1.8 m depth was determined near time of seeding and of harvest by neutron attenuation. The soil reached an upper drained limit of 0.20-0.25 m 3 m-3 water in a 1.8 m profile, equating to no more than 450 m water. Safflower and sunflower used ca. 500 mm water, more water than any of the other crops used. The greatest growing season water use efficiency was captured by the annual forage crop. Except following safflower and sunflower, soil water every spring was near the upper drained limit. Deep rooted crops can have a place in rotations on the semiarid northern Great Plains. But one must be prepared for variable yields and potential reduced yields following deep rooted crops, and for an occasional crop failure. Crop and soil management for alternative crops differ from that of small grain management, requiring some adaptation of management practices

Terrace formation in cropping strips protected by tall wheatgrass barriers

Tall wheatgrass barriers have been successfully tested in the northern Great Plains for wind erosion control and plant protection. Our objective was to document the passive formation of hillside terraces occasioned by grass barriers on a variable 2 to 4% west to east slope. Eleven double-row tall wheatgrass [Elytrigia elongata (Host) Nevski) barriers with 10 15-m-wide cropping intervals 530 m long were established in 1967 on a Williams loam (fine-loamy mixed, Typic Argiboroll) 11 km north of Culbertson, Montana. The barriers were oriented north and south in traditional field orientation. In 1991 we established four transects 15 m apart across the barrier system and designated five sampling points along the transects in each cropping interval for a total of 200 sampling points. To avoid confounding by slopes parallel to the barriers, we selected a segment of the barrier system on a near 0% north to south slope for the measurements. Elevation was determined at each point, and soil cores were taken to a depth of about 90 cm to determine depth to CaCO3 layer, and to determine total and organic carbon by 5 cm increments. A stair-step pattern, with a maximum drop of 30 cm from one grass barrier to an adjacent cropping interval, was documented. Depth to CaCO3 and organic carbon concentration increased downslope between barriers, showing soil movement. Grass barriers may serve as a substitute for mechanically built terraces

Water infiltration into a glacial till soil following subsoiling and secondary tillage

Water limits crop production in the semiarid northern Great Plains of the United States. Summer fallow is commonly practiced to store water in the soil for use by a later crop (Haas, el al., 1974). However, high evaporation rates makes summer fallowing inefficient in storing water (Tanka, 1985; Tanka and Aase, 1987). Additionally, the fallow-wheat (Triticum aestivum L.) crop sequence has been implicated as the cause of serious declines in soil organic carbon (Rasmussen and Parton, 1994). A recent report by Aase and Pikul (1995) showed that annually grown spring wheat was an acceptable alternative to the traditional fallow-wheat crop sequence in eastern Montana, USA. To successfully grow a crop every year, however, it is essential to conserve as much precipitation as possible between harvest and seeding. Specialized tillage is thought to improve water infiltration and soil water storage. Pikul et al. (1996) have shown that soil ripping on the contour may improve water infiltration into frozen soil and possibly increase soil water storage. Objectives were to 1) determine the effect of soil ripping on water infiltration and 2) evaluate the durability of tillage induced soil structure following repeated wetting and drying cycles

Wheat response and residual soil properties following subsoiling of a sandy loam in eastern Montana

Shallow tillage pans resulting from the use of the same tillage tools may lead to wheat (Triticum aestivum L.) yield reductions. We hypothesized that occasional deep tillage to fracture shallow tillage pans would improve water utilization and result in increased wheat yield. Our hypothesis was tested by comparing paired crop and soil responses on plots that were subsoiled using a paratill (PT) or not subsoiled (NOPT). Soil was a Dooley sandy loam (US soil taxonomy: fine-loamy, mixed Typic Argiboroll; FAO taxonomy: Kastanozem) derived in glacial till near Culbertson, Montana, USA. Effects of PT or NOPT were compared in a long-term cropping study that included annual wheat using no tillage (NT), annual wheat using fall and spring tillage (FST) and wheat rotated with fallow (FWCT). Plots that were subsoiled (PT) were paratilled once in autumn 1992 to about 0.3 m deep. Cone index of the top 0.3 m of soil 2.5 years after subsoiling was lower on PT (891 kPa) compared with NOPT (981 kPa). Soil bulk density was 1.34 Mg M -3 on PT and 1.36 Mg m-3 on NOPT plots. Final water infiltration rate averaged 15 mm h - on PT and 6 mm h - I on NOPT plots for nine months after subsoiling. Average water content of the top 1.2 m of soil in the spring of the year was 21 mm greater on PT than on NOPT plots. There were no differences due to treatments in wheat yield; average grain yield was 1820 kg ha 1 on annual wheat plots and 2380 kg ha-1 on wheat/fallow plots. Residual effects of subsoiling on soil properties were detected for 2.5 years after subsoiling, but soil changes attributed to subsoiling had no effect on wheat yield

Hayland conversion to wheat production in semiarid eastern Montana: tillage, yield and hay production comparisons

When converting grass- and haylands to cultivated crop production, care must be taken to conserve and maintain soil resources while considering economic issues. Methods of breaking sod can have a bearing on erosivity, physical and chemical properties of soils, and cost of production. Our objective was to compare three methods of converting crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schuh.] hayland to wheat (Triticum aestivum L.) production vs. leaving the land for hay production. We initiated a study in 1990 on Dooley sandy loam (fine-loamy, mixed Typic Argiboroll) near Froid in semiarid eastern Montana, USA. Plots, replicated three times, were 12- by 30-m oriented east to west on a north-facing slope. We converted sod to cultivated crop production by: (1) moldboard plow, (2) toolbar with sweeps, (3) herbicides (no-till). Plots were fallowed until spring 1991 and then seeded to spring wheat each of the next four years. All wheat plots were fertilized with 224 kg ha - I of 18-46-0 in 1991 and 1992, and 34 kg ha-1 nitrogen as 34-0-0 in 1993 and 1994. Grass was either fertilized same as wheat or not fertilized. Wheat yields averaged 2540 kg ha-1 on tilled treatments and 2674 kg ha-1 on no-till. Fertilized grass consistently out-yielded unfertilized, and averaged 3.2 Mg ha-1 vs. 1.8 Mg ha-1. Toolbar with sweeps had highest economic return of US$169.48 ha-1 to pay for land, labor, and management. Moldboard plow had US$162.05 ha-1 . Because of herbicide costs, no-till only returned US$148.64 ha-1 . Unfertilized grass hay returned US$67.68 ha-1 and fertilized grass hay, US$97.95 ha-1. Results may be tempered because our wheat yields were high: a 2016 kg ha-1 wheat yield would have returned the same as fertilized grass. Before converting grass- and hay-lands to small grains production, consideration must be given to such variables as sod conversion methods, management practices, labor requirements, market conditions, total precipitation and its temporal distribution, soil conditions, growth environment, soil conservation, and economic

Fallow replacement using indianhead lentils: water use, yield and oil nitrogen

Because of increased costs of fertilizer and evidence of declining soil quality there has been renewed interest in crop rotations using legumes in the traditional spring wheat-fallow rotation areas of the semiarid northern Great Plains. Objectives were to test a "green fallow" method of farming as a system to build soil nitrogen and efficiently use water. We compared mechanical fallow using sweeps (N1F) and chemical fallow (CF) to green fallow. Fallow treatments MF and CF received 30 lb-N/acre. as N1-14NO3 broadcast prior to seeding wheat (Triticum aestivum L.). Lentils (Lens culinaris Medikus, cv. `Indianhead') were grown as a green manure crop in a green fallow-spring wheat rotation. The experiment was started in 1991 as a randomized complete block with four replications and MF as control. Soil was a Williams loam ( fine-loamy, mixed Typic Argiboroll) 7 miles north of Culbertson Montana. At full bloom, lentils were either killed by disking (GMMF) or chemical burn-down (GMCF). Average dry-weight of Indianhead lentils for 1991, 1992, and 1993 was 1500 lb/acre compared to an average of 4700 lb/acre for 1994 and 1995. Average water use by lentils in 1991, 1992, and 1993 was 10.6 inches. In contrast, MF and CF lost 9.9 inches. Average water use by lentils in 1994 and 1995 was 12.9 inches which was significantly more than the loss of 10.7 inches on MF and CF. At spring planting, there were no differences in soil water content among treatments. Wheat yield was 25% less on green fallow compared to MF and CF. Soil NO3 -N levels were 35 % lower on green fallow rotations than MF and CF rotations. There were no differences among treatments in nitrogen mineralization rates in 1993 following two cycles of green manure. Lack of available nitrogen, rather than lack of soil water, appears to have restricted wheat production on green fallow treatments

Water use and biomass production of oat-pea hay and lentil in a semiarid climate

Suitability of alternative crops in the northern Great Plains remains a question because of water limitations. Objectives were to compare water use of an oat (Avena sativa L.)—pea (Pisum sativum L.) mix grown for hay (OPH) to that of black lentil (Lens culinaris Medikus cv. Indianhead) grown as green manure (BL). Water use and plant biomass for OPH and BL were measured near Culbertson, MT (Site 1), during 4 yr. Soil water was measured by neutron attenuation. Precision-weighing lysimeters were used at Site 2, located 65 km southeast of Site 1, to measure water use. Soil was a Williams loam (fine-loamy, mixed, superactive, frigid Typic Argiustolls). Biomass of crops was measured biweekly. Relative feed value (RFV) based on measured neutral detergent fiber and acid detergent fiber was calculated. Biomass under OPH was 34 and 46% greater than with BL at Sites 1 and 2, respectively. At Site 1, biomass accumulated at a rate of 14 kg ha-1 mm-1 water used under BL and 23 kg ha -1 mm- 1 under OPH. Biomass accumulated at a rate of 21 kg ha- 1 mm-1 under BL and 29 kg ha -1 mm -1 under OPH at Site 2. Hay RFV, at full bloom in pea, averaged 116 (Number 2 hay), and this did not change appreciably as the crop matured to soft dough stage in oat. Oat—pea hay fits the growing conditions in the northern Great Plains and meets the needs of producers for high quality hay

Contour ripping: A tillage strategy to improve water infiltration into frozen soil

Practices that combine stubble management for snow catch and contour-ripping for snowmelt infiltration have potential to increase water infiltration and soil water storage. Our objective was to investigate sod lapping to improve water infiltration into frozen soil. Infiltration studies on frozen soil were conducted at sites near Pendleton, Oregon (silt loam soil), and Culbertson, Montana (sandy loam soil). Ripping was performed with a single chisel or parabolic subsoiling shank at 6- to 8-m intervals on the contour to a depth of 0.2 to 0.3 m. Final infiltration rate on the sandy loam averaged 11 mm h-1 on the rip treatment and 1 mm h-1 on the no-rip treatment even when the soil was frozen deeper than 0.6 m. On the silt loam soils, when the average depth of frozen soil was 0.14 m, average final infiltration rate was 28 mm h-1 on the rip treatment and 2 mm h-1 on the no-rip treatment. There were no treatment differences on the silt loam when the soil was frozen 0.35 in. Soil condition at the time of ripping determined the effectiveness of tillage to improve water infiltration; there was little benefit from ripping a dry pulverized soil because loose soil flowed into the rip and obliterated the rip path. Desirable macropore structure on loose soil was achieved by deferring ripping until the soil was frozen. Infiltration measurements show that soil ripping has potential to increase water infiltration and consequently decrease water runoff, and if used in conjunction with stubble management to maximize snow trapping, may increase overwinter soil water storage

Cropping system effects on soil quality in the Great Plains: Synthesis from a regional project

Soils perform a number of essential functions affecting management goals. Soil functions were assessed by measuring physical, chemical, and biological properties in a regional assessment of conventional (CON) and alternative (ALT) management practices at eight sites within the Great Plains. The results, reported in accompanying papers, provide excellent data for assessing how management practices collectively affect agronomic and environmental soil functions that benefit both farmers and society. Our objective was to use the regional data as an input for two new assessment tools to evaluate their potential and sensitivity for detecting differences (aggradation or degradation) in management systems. The soil management assessment framework (SMAF) and the agro-ecosystem performance assessment tool (AEPAT) were used to score individual soil properties at each location relative to expected conditions based on inherent soil-forming factors and to compute index values that provide an overall assessment of the agronomic and environmental impact of the CON and ALT practices. SMAF index values were positively correlated with grain yield (an agronomic function) and total organic matter (an agronomic and environmental function). They were negatively correlated with soil nitrate concentration at harvest (an indicator of environmental function). There was general agreement between the two assessment tools when used to compare management practices. Users can measure a small number of soil properties and use one of these tools to easily assess the effectiveness of soil management practices. A higher score in either tool identifies more environmentally and agronomically sustainable management. Temporal variability in measured indicators makes dynamic assessments of management practices essential. Water-filled pore space, aggregate stability, particulate organic matter, and microbial biomass were sensitive to management and should be included in studies aimed at improving soil management. Reductions in both tillage and fallow combined with crop rotation has resulted in improved soil function (e.g., nutrient cycling, organic C content, and productivity) throughout the Great Plains