Summer Fallow Research Articles

Yield attributes, yields and nutrient uptake of Basmati rice (Oryza sativa) as influenced by in-situ and ex-situ green manuring crops and zinc fertilization

A field experiment was conducted in a split plot design at the research farm of ICAR-Indian Agricultural ResearchInstitute (IARI), New Delhi during summer and kharif seasons of 2015 and 2016 to study the influence of in-situ and ex-situ green manuring and zinc fertilization on nutrient uptake, yield attributes, correlation between yield and yield attributes, and yield of Basmati rice (Oryza sativa L.). Results of this study revealed that the incorporation of Sesbania aculeata green manure @ 33.8 and 35.6 t/ha prior to transplanting of Basmati rice during 2015 and 2016, respectively resulted in higher yield attributes and yield of Basmati rice compared with Vigna umbellata, Leucaena leucocephala and summer fallow during both the years. Foliar application of 0.5% solution of chelated Zn-EDTA at 20, 40, 60 and 80 days after transplanting (DAT) was better than soil application of Zn with regard to yield attributes and yield of Basmati rice and uptake of nutrients by the crop. In general, there was significant and positive correlation of grain yield with yield attributes. The uptake of nutrients by the crop was highest with incorporation of Sesbania aculeata and lowest in summer fallow.

Influence of summer legume residue recycling and varietal diversification on productivity, energetics, and nutrient dynamics in basmati rice–wheat cropping system of western Indo-Gangetic Plains

ABSTRACTA field experiment was conducted on summer mungbean residue recycling (SMBRR) and basmati rice–wheat cropping system (BRWCS) at New Delhi, India. The SMBRR enhanced the system productivity and net returns by ∼19.1% and 22.1% compared to summer fallow (SF) with highest magnitude under genotypic sequence of P 2511/HD 2967. Two genotypes each in basmati rice (PB 1 and P 2511) and wheat (HD 2967 and HD 2733) responded well to SMBRR with respect to grain yield efficiency index (GYEI) ≥ 1.0. SMBRR also registered ∼13.5% higher microbial biomass carbon (MBC) than SF. Soil organic carbon (SOC) storage also increased by ∼6.8% in 0–30 cm soil layer. The rice–wheat–summer mungbean system produced significantly highest energy efficiency compared to the rice–wheat–summer fallow system with highest values under genotypic sequence of P 2511/HD 2967 as a result of better yield expression. Overall, SMBRR with suitable genotypic sequence improved the system productivity, profitability, and nutrient dynamics in BRWCS, which are vital for long-term sustainability of this system.

Response of yield increase for dryland winter wheat to tillage practice during summer fallow and sowing method in the Loess Plateau of China

Soil moisture is the most critical limiting factor impacting yields of dryland winter wheat (Triticum aestivum L.) and it is strongly affected by tillage practice and sowing methods. This study was to assess the link between sowing method and tillage practice during summer fallow and their subsequent effect on soil moisture and grain yield. Furthermore, we sought to identify a more appropriate farming management practice for winter wheat production in Loess Plateau region of China. The experiment was conducted from 2011 to 2013, using a two-factor split plot design, including subsoiling (SS) or no tillage (NT) during summer fallow for main plots, and conventional drill sowing (DS) or plastic film drill sowing (FM) for subplots. Results showed that the maximum soil water storage (SWS) was under SS×FM treatment with values of 649.1 mm (2011–2012) and 499.4 mm (2012–2013). The SWS during the 2011–2012 growing season were 149.7 mm higher than that in the 2012–2013 growing season. And adoption of SS×FM significantly increased precipitation use efficiency (PUE) and water use efficiency (WUE) compared to other treatments for both seasons. Moreover, adoption of SS×FM significantly increased yield by 13.1, 14.4, 47.3% and 25.9, 39.1, 35.7% than other three treatments during the two growing seasons, respectively. In summary, combining subsoiling during summer fallow with plastic film drill sowing (SS×FM) increased SWS at sowing and effectively improved WUE, thus representing a feasible technology to improve grain yield of dryland winter wheat in the Loess Plateau of China.

Effects of combined application of chemical fertilizer and organic manure on wheat yield and leaching of residual nitrate-N in dryland soil

The effects of optimum nitrogen (N) fertilization rate with and without adding manure on wheat yield and leaching of residual nitrate-N in soil profile were examined in Weibei dryland, Shaanxi with a field experiment combined different N fertilization rates (0, 75, 150, 225, 300 kg N·hm-2) and organic manure (0 and 30 t·hm-2). The results showed that, compared to chemical N fertilizer, combined application of inorganic fertilizer and organic manure increased winter wheat yield by 14.7% when N fertilization rate was reduced by 27.1%. The highest yield was obtained when 150 kg·hm-2 of N rate was combined with the manure (N150+M). The combination of N fertilizer and manure promoted N uptake of wheat grain and increased N use efficiency by 20.2%. The highest N use efficiency was recorded in the N150+M treatment. In addition, the lea-ching of residual nitrate-N during the wheat growing season and the leaching of nitrate-N during summer fallow were decreased. When N application rate was lower than 115 kg·hm-2, N fertilizer combined with organic manure reduced the amount of nitrate-N leaching in summer fallow. We recommend the combined application of organic manure with about 150 kg·hm-2 of N fertilizers in Weibei dryland to guarantee high winter wheat yield, N use efficiency, and reduce excessive residue of fertilizer N in the soil.

Relay-cropping and Fallow Programs for Strawberry-based Production System: Effects on Crop Productivity and Weed Control

Many strawberry growers in Florida relay crop vegetables with strawberries or grow multiple crops on the same plastic mulch. The practice can reduce the overall input costs per crop but weed management can be problematic. Field experiments designed as a split plot were conducted in Balm and Dover, FL over two successive strawberry-growing seasons from Oct. 2014 to Mar. 2015 (year 1) and Oct. 2015 to Mar. 2016 (year 2) and two successive muskmelon-growing seasons from March to July 2015 (year 1) and March to July 2016 (year 2). The objectives were to examine the effect of summer fallow programs and the presence or absence of a relay-crop on weed density and strawberry (Fragaria ×ananassa Duchesne) and muskmelon (Cucumis melo L.) yields. Summer fallow programs included leaving the plastic mulch in place and reusing it in year 2, a sunn hemp (Crotalaria juncea L.) cover crop, or a conventional chemical fallow. Relay cropping muskmelon with strawberries had no effect on strawberry yield. Summer fallow programs had no effect on muskmelon growth and yield in Balm and Dover, as well as strawberry growth and yield in Balm. In Dover, the plastic mulch summer fallow had 22% to 34% lower berry yield in year 2 compared with cover crop and chemical fallow, respectively. In year 2, relay-cropping was more effective in reducing total weed density compared with strawberry monoculture in Dover but not in Balm. In year 2 in Dover, averaged overall summer fallow programs, the total weed density was ≈3-fold less in relay-cropping than strawberry monoculture. Of all the summer fallow programs evaluated, leaving the plastic mulch in place combined with glyphosate was the most effective summer fallow program, whereas the conventional chemical fallow was the least effective at weed suppression. We conclude that relay cropping or double use of plastic mulch for successive strawberry crops are viable options for Florida strawberry growers.

Intensifying rotations increases soil carbon, fungi, and aggregation in semi-arid agroecosystems

Increasing soil organic carbon (SOC) is a critical but daunting challenge in semi-arid agroecosystems. For dryland farmers, low levels of SOC and aggregation exacerbate the risks of farming in a water-limited environment − risks that will compound with climate change. Many dryland farmers in semi-arid climates use year long periods called summer fallow, where no crops are grown and weeds are controlled, to store rainwater and increase the yield of the following crop. In semi-arid climates around the world, dryland farmers are increasingly replacing summer fallow with a crop, a form of cropping system intensification. Cropping system intensification has the potential to increase SOC, but the drivers of this effect are unclear, and may change based on environmental conditions and management strategy. We quantified SOC, water-stable aggregates, and fungal and microbial biomass on 96 dryland, no-till fields in the semi-arid Great Plains, USA, representing three levels of cropping system intensity from wheat-fallow to continuous (no summer fallow) rotations along a potential evapotranspiration gradient. Cropping system intensity was positively associated with SOC, aggregation, and fungal biomass, and these effects were robust amidst variability in environmental and management factors. Continuous rotations averaged 1.28% SOC at 0–10 cm and had 17% and 12% higher SOC concentrations than wheat-fallow in 0–10 cm and 0–20 cm depths, respectively. Aggregate stability in continuous rotations was about twice that in wheat-fallow rotations. Fungal biomass was three times greater in continuous rotations than wheat-fallow, but was not significantly different from mid-intensity rotations. Using structural equation modeling, we observed that continuous cropping, potential evapotranspiration, % clay content, and fungal biomass together explained 50% of the variability in SOC, and that SOC appears to enhance aggregation directly and as mediated through increases in fungal biomass. Overall, the model suggests that cropping system intensity increases SOC both directly, through greater C inputs to soil, and indirectly, by increasing fungal biomass and aggregation. Our findings suggest that continuous cropping has the potential to provide gains in SOC and soil structure that will help offset C emissions and enhance the resilience of dryland agroecosystems.

Effects of green manures during fallow on moisture and nutrients of soil and winter wheat yield on the Loss Plateau of China

The application of catch crops as a green manure can enhance soil fertility owing to improving soil nutrients. We conducted one year field experiment to evaluate the effect of catch crops [Rapeseed (Brassica napus L.) under different sowing rates and Soy bean (Glycine max L.)] with biological organic fertilizer 1,500 kg/ha on wheat yield and soil nutrients. The green manures were sown on 3th July 2015 during summer fallow. At the beginning, there were five treatments as follows: R1 (Rapeseed and sowing rate was 7.5 kg/ha); R2 (Rapeseed and sowing rate was 15 kg/ha); R3 (Rapeseed and sowing rate was 22.5 kg/ha); S (Soy bean and sowing rate was 105 kg/ha); C (Control was bare field). Every green manure treatment was split into two treatments on 27th September 2015. One treatment we turned the above ground biomass of green manure into the soil. And another treatment we harvested the above ground biomass of green manure. The above ground biomass turned into soil treatments were G1, G3, G5 and G7. The above ground biomass harvested treatments were G2, G4, G6 and G8. The treatment C was still the bare field. Soil samples were taken twice to measure soil moisture and nutrients at two stages. One stage was in autumn before winter wheat sowing and another stage was in next year summer after wheat harvest. The significantly highest 1,000-grain weight and grain yield belonged to the treatment C, which were 10.69%-36.87% and 16.86%-72.5% higher than that of the green manures treatments. After wheat harvest, the 0-20 cm soil available N and total N of G7 were 51.40%-20.45% and 95.12%-125.35% significantly better than that of other treatments. The significantly highest soil total P of 0-20 cm belonged to G3 after wheat harvest, which was 25%-45.83% better than other treatments. Before wheat sowing, the treatment C kept the significantly lowest soil available K of five layers. The 0-20 cm and 20-40 cm soil organic matter of the treatment S was 40.28%-71.12% and 53.92%-122.67% significantly higher than other treatments before wheat sowing. Therefore, growing rapeseed and soy bean during summer fallow in this region significantly reduced 1,000-grain weight and grain yield of subsequent winter wheat. But the incorporation of green manures improved the soil nutrients to some extent.

Phosphorus efficiency, soil phosphorus dynamics and critical phosphorus level under long-term fertilization for single and double cropping systems

Wise phosphorus (P) management is paramount to ensure food and environmental security and prolong the life of P resources. Long-term experiments under winter wheat–summer maize (with irrigation) and winter wheat–summer fallow (rain-fed) cropping systems were undertaken to investigate P efficiency, soil P availability and P downward movement in the deep profile of a loess soil in China. The four nutrient management regimes in each experiment were: a control without any nutrient input; P and K combined (PK); N, P and K combined (NPK), and organic manure (M) combined with NPK (MNPK). The P efficiency ranged from 20 to 54% under the double cropping system, and from 13 to 33% in the single cropping system over the 25 years studied, and the highest P efficiency was in the NPK treatment in both systems. Application of P significantly increased soil total-P, Olsen-P and CaCl2-P over the years, especially in the MNPK treatment. Two segment regression analyses indicated that Olsen-P was about 14 mg kg−1 or 16 mg kg−1 for optimal crop yield under double cropping or single cropping. In addition, Olsen-P content above 37 mg kg−1 or 57 mg kg−1 led to a significant increase in CaCl2-P content under double cropping or single cropping, which might indicate risk of P leaching. After 24 years of P applications, total P accumulated at various depths depending on treatment under double cropping, but there was no accumulation under single cropping. While Olsen-P leached down to a depth of 300 cm in the MNPK treatments under both cropping systems, and higher concentrations were recorded in the deeper layers in single cropping than in double cropping systems. The Olsen-P leached to a shallower depth in the PK and NPK treatments under single cropping compared to double cropping. We conclude that P supply in excess of the crop’s requirement (e.g. MNPK) or an unbalanced nutrient supply (e.g. PK) resulted in not only low P efficiency and massive accumulation of P in the topsoil but also leaching out of root zone under both irrigated and rain-fed conditions in the loess soil. Thus, P fertilization recommendations need to be adjusted based on changes in soil P over time.

Soil properties influenced by summer fallow management in the Horse Heaven Hills of south central Washington

The Horse Heaven Hills (HHH) is the world9s driest rainfed wheat (<i>Triticum aestivum</i> L.) region where soils are highly susceptible to wind erosion due to use of tillage during the fallow phase of the winter wheat–summer fallow (WW-SF) cropping system. Wheat straw residue biomass and cover, surface roughness, soil water content and strength, and aggregate size distribution of no-tillage fallow (NTF), undercutter-tillage fallow (UTF), and traditional-tillage fallow (TTF) were measured after primary tillage of UTF and TTF in late April and after sowing winter wheat in late August of 2007 at two sites in the HHH. Residue cover and silhouette area index were at least two times greater and penetration resistance and shear stress were at least five times greater for NTF than TTF in spring and late summer at both sites. Random roughness was typically lower for NTF as compared with UTF in spring and late summer at both sites. Summer fallow treatments influenced soil aggregation whereby geometric mean diameter was greater and erodible fraction was lower for NTF than TTF. Based upon the Revised Wind Erosion Equation (RWEQ), sediment flux was lowest for NTF and at least 70% lower for UTF as compared with TTF. Thus, soil loss due to wind erosion can be reduced by using NTF and UTF rather than TTF for WW-SF rotations in the HHH.

Integrated control of weeds at growing winter wheat after summer fallow

Integrated control of weeds at growing winter wheat after summer fallow

Surface Moistening Trends in the Northern North American Great Plains Increase the Likelihood of Convective Initiation

Abstract Land management impacts atmospheric boundary layer processes, and recent trends reducing the practice of summer fallow have led to increases in precipitation and decreases in temperature in the Canadian Prairie provinces during summer. It is unclear if such trends also impact the hydrometeorology of the adjacent U.S. northern Great Plains, parts of which have seen similar changes in land management. Here, MERRA-2 reanalysis data, eddy covariance observations, and a mixed-layer (ML) atmospheric modeling framework are combined to demonstrate that the likelihood of convectively preconditioned conditions has increased by approximately 10% since the mid-1980s and is now more sensitive to further decreases in the Bowen ratio (Bo) and maximum daily net radiation in northeastern Montana. Convective season Bo in the study area has decreased from approximately 2 to 1 from the 1980s until the present, largely due to simultaneous increases in latent heat flux and decreases in sensible heat flux, consistent with observed decreases of summer fallow and increases in cropping. Daily net radiation has not changed despite a significant decrease in May and June humidity lapse rates from the 1980s to present. Future research should determine the area of the U.S. Great Plains that has seen changes in the dynamics of the atmospheric boundary layer height and lifted condensation level and their crossings as a necessary condition for convective precipitation to occur and ascertain if ongoing changes in land management will lead to future changes in convective outcomes.

Soil physical properties response to tillage practices during summer fallow of dryland winter wheat field on the Loess Plateau.

Soil physical properties are a greatly important part of the soil and indicator of soil quality, which can directly affect soil nutrient turnover and crop yields in dryland. This study was carried out with three tillage practices during the summer fallow season since 2011, including no tillage (NT), plow tillage (PT), and subsoiling (ST) in dryland winter wheat fields of the Loess Plateau. Results showed that soil tillage during the summer fallow had a small effect on soil bulk density (ρ b) in the 0-50-cm soil profile before sowing and after harvesting of winter wheat. Soil ρ b under NT at a depth of 20-30cm was significantly greater than those under PT in both seasons. Both soil gravimetric water content (θ g) and volumetric moisture content (θ v) after harvesting increased by 28.8-78.6% and 37.5-87.3%, respectively, compared with those before sowing. Adoption of PT significantly increased soil θ g and θ v in the entire 0-50-cm profile before sowing compared with NT and ST (P<0.05). In addition, there was a small effect on soil porosity (e.g., total porosity, air-filled porosity, and capillary porosity) in the profile of 0-50cm both before sowing and after harvesting. Overall, short-term tillage during summer fallow mainly affected soil water content in the 0-50-cm soil profile, and it had a slight effect on other physical soil properties.

Biology, agricultural impact, and management of Cyperus rotundus L.: the world’s most tenacious weed

Purple nutsedge (Cyperus rotundus L.), a troublesome weed, is economically damaging weed, which is widely naturalized in the tropical and subtropical regions of the world. This weed has been reported to cause 20–90% yield losses in various agronomic and horticultural crops across the world. Perennial nature, genetic diversity, ability to tolerate adverse climatic conditions, high rate of reproduction, ease-of-dispersion, strong competitive abilities, and allelopathic potential assist this weed to thrive in a range of agro-climatic regions. Routine cultural approaches, including crop rotation, crop choice, and mechanical cultivation, are ineffective in achieving season-long management of C. rotundus. Pre-emergent and post-emergent herbicides, as well as myco-herbicides, can control its growth but fail to limit the regenerative capacity and tuber viability of C. rotundus in the long term. Integration of herbicides with tillage operations during summer fallows would be a reliable option to desiccate the tubers and rhizomes of C. rotundus. Furthermore, preventive measures as well as complete destruction of nascent foci would be helpful in preventing future spread of this weed. This review will help researchers and scientists in understanding the reproductive biology and future threats of C. rotundus, leading towards the development of improved control methodologies. The information presented in this article will also enable researchers and growers to address the prevailing gaps in the eco-biology of this weed for the long-term control of C. rotundus in economically important field crops.

Evaluation of long-term conservation agriculture and crop intensification in rice-wheat rotation of Indo-Gangetic Plains of South Asia: Carbon dynamics and productivity.

In the context of deteriorating soil health, stagnation of yield in rice-wheat cropping system (RWCS) across Indo- Gangetic plains (IGP) and environmental pollution, a long term field experiment was conducted during 2009-2016 taking four crop scenarios with conservation agriculture (CA), crop intensification and diversified cropping as intervening technology aiming to evaluate the sustainability of the systems. Scenario 1 (S1) represented conventional farmers' practice of growing rice and wheat with summer fallow. In scenario 2 (S2) and scenario 3 (S3), legume crop was taken along with rice and wheat with partial CA and full CA, respectively. Conventional RWCS was replaced with rice-potato+maize- cowpea cropping system with partial CA in scenario 4 (S4). The S3 scenario registered highest total organic carbon (TOC) stock of 47.71 Mg C ha-1 and resulted in significant increase of 14.57% over S1 (Farmer's practice) in 0-30cm soil depth after 7 years of field trial. The S4 scenario having intensified cropping systems recorded lowest TOC of 39.33 Mg C ha-1 and resulted in significant depletion of 17.56% in C stock with respect to S3 in 0-30cm soil depth. The TOC enrichment was higher in S2, S3 and S4 scenario in the surface soil (0-10cm) compared to S1. At lower depth (20-30cm), the TOC enrichment was significantly higher in S2 (12.82 Mg C ha-1) and S3 (13.10 Mg C ha-1 soil) over S1 scenario. The S2 and S3 scenario recorded highest increased allocation of TOC (3.55 and 6.13 Mg C ha-1) to passive pool over S1. The S2 (15.72tha-1), S3 (16.08tha-1) and S4 (16.39tha-1) scenarios recorded significantly higher system rice equivalent yield over S1 (10.30tha-1). Among the scenarios, S3 scenario had greater amount of total soil organic carbon, passive pool of carbon and higher system rice equivalent yield, thus, is considered the best cropping management practice to maintain soil health and food security in the middle IGP.

Coupling life-cycle assessment and the RothC model to estimate the carbon footprint of green manure-based wheat production in China

Reducing the carbon footprint (CF) of crop production is an efficient way to mitigate climate change. Growing legume green manure (LGM) instead of summer fallow may achieve this goal by lowering synthetic nitrogen (N) fertilizer needs and replenishing the depleted soil carbon (C) pool. The Rothamsted Carbon (RothC) model was incorporated into the Life-Cycle Assessment (LCA) to evaluate the present and projected CFs of green manure-based wheat production systems in dryland agriculture on the Loess Plateau of China. The field study included four main treatments (Huai bean, soybean and mung bean grown as green manure in summer and fallow as control) and four synthetic N rates (0, 108, 135 and 162kgNha−1) applied at wheat sowing. Soybean as LGM increased averaged wheat yield over 4 synthetic N rates by 8% compared with fallow (P<0.05), and synthetic N requirement was reduced by 33% without compromising the wheat yield for all the main treatments. Although LGM treatments had higher greenhouse gas (GHG) emissions from agricultural inputs, the greater amount of C inputs elevated the corresponding SOC stocks (SOCS) by 14–24% after 8years, thus significantly reducing the CF by 25–51% compared with fallow. The modelled SOCS equilibrium indicates that the CF for cropping systems with LGM will be 53–62% lower than fallow and 23–37% lower compared with their current level. In conclusion, introducing legume green manure instead of summer fallow is a highly efficient measure for persistent CF reduction, and coupling the RothC model and LCA is an alternative method to predict the long-term impact of different cropping systems on GHG emissions.

Wind Erosion and PM10 Emissions from No‐Tillage Cropping Systems in the Pacific Northwest

Core Ideas Erosion of agricultural lands affect air quality in the Inland Pacific Northwest. Alternatives to tillage‐based cropping systems are needed to reduce wind erosion. No‐tillage cereal cropping systems reduce wind erosion and particulates ≤10 µm in diameter emissions. Economically viable strategies are sought for no‐tillage cropping systems. Wind erosion is a concern in the Inland Pacific Northwest (PNW) of the United States where the emission of particulates ≤10 µm in diameter (PM10) from winter wheat (Triticum aestivum L.)/summer fallow (WW/SF) dryland cropping systems during high winds degrades air quality. There is a potential to reduce the risk of wind erosion using no‐tillage or chemical fallow cropping systems, but wind erosion observations are lacking from these systems. We measured sediment and PM10 flux from reduced‐tillage WW/SF, no‐tillage wheat/chemical fallow (NTW/CF), and no‐tillage spring barley (Hordeum vulgare L.)/spring wheat (NTSB/SW) using a portable wind tunnel near Ralston, WA. Horizontal sediment flux, wind speed, and PM10 concentration were measured over two consecutive 10 min sampling periods inside the tunnel after sowing wheat in spring or late summer on four replications of the rotations. Sediment flux was measured with a modified Bagnold type sampler while wind speed and PM10 concentration were respectively measured with pitot tubes and aerosol monitors positioned at six heights above the soil surface inside the tunnel. Sediment and PM10 fluxes were an order of magnitude greater in late summer than spring. After sowing wheat in spring, sediment and PM10 fluxes were greater for the NTSB/SW than NTW/CF rotation while, after sowing winter wheat in late summer, sediment and PM10 fluxes were greater for the WW/SF than the NTSB/SW rotation. Our results suggest that wind erosion and PM10 emissions can be significantly reduced using no tillage cropping systems in the PNW.

Re‐inventing Austrian winter pea Towards developing food quality winter peas

In the dry areas of the Pacific Northwest where the typical rotation is winter wheat–summer fallow, farmers need a broadleaf rotational crop to improve the sustainability of the cropping system. Fall‐sown, food quality, winter peas are poised to fill that need. Earn 2 CEUs in Crop Management by reading this article and taking the quiz at https://www.certifiedcropadviser.org/education/classroom/classes/487

Impact of Climate Change Adaptation Strategies on Winter Wheat and Cropping System Performance across Precipitation Gradients in the Inland Pacific Northwest, USA

Ecological instability and low resource use efficiencies are concerns for the long-term productivity of conventional cereal monoculture systems, particularly those threatened by projected climate change. Crop intensification, diversification, reduced tillage, and variable N management are among strategies proposed to mitigate and adapt to climate shifts in the inland Pacific Northwest (iPNW). Our objectives were to assess these strategies across iPNW agroecological zones and time for their impacts on 1) winter wheat (Triticum aestivum L.) productivity, 2) crop sequence productivity and 3) N fertilizer use efficiency. Region-wide analysis indicated that WW yields increased with increasing annual precipitation, prior to maximizing at 520 mm yr-1 and subsequently declining when annual precipitation was not adjusted for available soil water holding capacity. While fallow periods were effective at mitigating low nitrogen (N) fertilization efficiencies under low precipitation, efficiencies declined as annual precipitation exceeded 500 mm yr-1. Variability in the response of WW yields to annual precipitation and N fertilization among locations and within sites supports precision N management implementation across the region. In years receiving less than 350 mm precipitation yr-1, WW yields declined when preceded by crops rather than summer fallow. Nevertheless, WW yields were greater when preceded by pulses and oilseeds rather than wheat across a range of yield potentials, and when under conservation tillage practices at low yield potentials. Despite the yield penalty associated with eliminating fallow prior to WW, cropping system level productivity was not affected by intensification, diversification, or conservation tillage. However, increased fertilizer N inputs, lower fertilizer N use efficiencies, and more yield variance may offset and limit the economic feasibility of intensified and diversified cropping systems.

Fallow replacement and alternative nitrogen management for reducing nitrate leaching in a semiarid region

Nitrate (NO3−) leaching into groundwater is a growing global concern for health, environmental, and economic reasons, yet little is known about the effects of agricultural management practices on the magnitude of leaching, especially in dryland semiarid regions. Groundwater nitrate–nitrogen (nitrate–N) concentrations above the drinking water standard of 10 mg L−1 are common in the Judith River Watershed (JRW) of semiarid central Montana. A 2-year study conducted on commercial farms in the JRW compared nitrate leaching rates across three alternative management practices (AMP: pea, controlled release urea, split application of N) and three grower standard practices (GSP: summer fallow, conventional urea, single application of urea). Crop biomass and soil were collected at ten sampling locations on each side of a management interface separating each AMP from its corresponding GSP. A nitrogen (N) mass balance approach was used to estimate the amount of nitrate leached annually. In 2013, less nitrate leached the year after the pea AMP (18 ± 2.5 kg N ha−1) than the year after the fallow GSP (54 ± 3.6 kg N ha−1), whereas the two AMP fertilizer treatments had no effect on nitrate leaching compared to GSPs. In 2014, leaching rates did not differ between each AMP and its corresponding GSP. The results suggest that replacing fallow with pea has the greatest potential to reduce nitrate leaching. Future leaching research should likely focus on practices that decrease deep percolation, such as fallow replacement with annual or perennial crops, more than on N fertilizer practices.

Weed Seed Fate during Summer Fallow: The Importance of Seed Predation and Seed Burial

Maximizing weed seed exposure to seed predators by delaying post-harvest tillage has been suggested as a way to increase weed seed loss to predation in arable fields. However, in some areas of northeastern Spain, fields are still tilled promptly after cereal harvest. Tillage usually places seeds in a safer environment compared to the soil surface, but it can also increase seed mortality through seed decay and fatal germination. By burying the seeds, tillage also prevents weed seed predation. Weed seed fate in a tilled vs. a no-till environment was investigated during the summer fallow months in three cereal fields in semi-arid northeastern Spain. Rigid ryegrass and catchweed bedstraw seeds were used. Predation rates were measured in a no-till area within each field in 48-h periods every 3 wk, and long-term predation rates were estimated. Fate of buried seeds was measured by burying 20 nylon bags with 30 seeds of each weed species from July to September at a depth of 6 cm in a tilled area contiguous to the no-till area. Predation rates over the entire summer were 62% and 49% for rigid ryegrass and catchweed bedstraw, respectively. High availability of crop seeds (preferred by ants) on the soil surface may have decreased predation of weed seeds early in the season. Seed loss due to burial was 54% and 33% for rigid ryegrass and catchweed bedstraw, respectively. Unusual above-average precipitation probably prompted higher than normal weed germination rates (fatal germination) in some fields, and thus led to higher seed mortality rates compared with an average year. These results suggest that leaving the fields untilled after harvest may be the optimum strategy to reduce inputs to the weed seedbank during the summer fallow period in semi-arid systems.