Fallow Cropping System Research Articles

Spring Wheat Response to Tillage System and Nitrogen Fertilization within a Crop–Fallow System

Spring wheat (Triticum aestivum L.) production in the northern Great Plains generally utilizes conventional tillage systems. A 12‐yr study evaluated the effects of tillage system [conventional‐till (CT), minimum‐till (MT), and no‐till (NT)], N fertilizer rate (0, 22, and 45 kg N ha−1), and cultivar (Butte86 and Stoa) on spring wheat grain yields in a dryland spring wheat–fallow rotation (SW–F). Butte86 yields with CT exceeded NT yields in five out of 12 years with 0 and 22 kg N ha−1 applied, and four years with 45 kg N ha−1 applied. Stoa yields with CT exceeded NT yields in three out of 12 years with no N applied, four years with 22 kg N ha−1 applied, and only one year with 45 kg N ha−1 applied. Yields with NT exceeded those with CT in one year. Most years, yields with MT equaled those with CT. Responses to N tended to be greatest in years when spring soil NO3–N was lowest. Positive yield responses to N fertilization with CT occurred in three years with Butte86 and two years with Stoa; with MT, four years with Butte86 and two years with Stoa; and with NT, five years with Butte86 and three years with Stoa. Cultivars were not consistent in their response to tillage and N fertilization. These results indicate that farmers in the northern Great Plains can successfully produce spring wheat in a SW–F system using MT and NT systems, but yields may be slightly reduced when compared with CT systems some years.

Spring Wheat Response to Tillage System and Nitrogen Fertilization within a Crop–Fallow System

Spring Wheat Response to Tillage System and Nitrogen Fertilization within a Crop–Fallow System

Soil Quality Assessment after Weed‐Control Tillage in a No‐Till Wheat–Fallow Cropping System

Adoption of reduced‐tillage fallow systems in the western USA is limited by winter annual grass weeds such as downy brome (Bromus tectorum L.). Moldboard plowing is an effective means of controlling downy brome in winter wheat (Tritcum aestivum L.)–fallow systems. The purpose of this study was to assess the influence of plowing and secondary tillage operations, for the purpose of weed control, on soil quality attributes of a silt loam soil that had been cropped in a sub‐till or no‐till (NT) winter wheat–fallow system for more than 20 yr. Compared with undisturbed NT, downy brome populations in plowed NT decreased 97 and 41% in the first and third crops following tillage, respectively. Wheat yields in plowed NT treatments were 30 and 9% greater in the first and third crops following tillage, respectively, compared with undisturbed NT. Soil quality indicators assessed were organic C (OC), total N, inorganic N, pH, electrical conductivity, bulk density, water infiltration rate, and pore‐size distribution. Five years after tillage, soil OC decline in the 0‐ to 7.5‐cm depth was 20% in plowed compared with undisturbed NT; however, OC increased 15% in the 7.5‐ to 15‐cm depth and was not different in the 0‐ to 30‐cm depth. Total soil N followed similar trends. Soil inorganic N in plowed NT decreased 37%, and soil pH increased 9%, compared with undisturbed NT, at the 0‐ to 7.5‐cm depth. Occasional tillage with the moldboard plow in a reduced‐ or no‐tillage management system will help control winter annual grass weeds, while retaining many of the soil quality benefits of conservation‐tillage management.

AN IMPROVED COVER CROP-FALLOW SYSTEM FOR SUSTAINABLE MANAGEMENT OF LOW ACTIVITY CLAY SOILS OF THE TROPICS

The potential of planted leguminous cover crop fallow as an alternative to the natural regrowth fallow for sustaining the productivity of low activity clay (LAC) soils in the tropics as the fallow period shortens was tested at Ibadan in the forest-savanna zone of southwestern Nigeria. The study, initiated in 1990, compared an improved system (cover crop-fallow) and a traditional system (natural fallow), with the aim of developing an improved cover crop-fallow system for sustainable management of LAC soils of the tropics. Pueraria phaseoloides, an herbaceous, N-fixing, perennial legume with a slow initial growth habit, was selected as a test cover crop. Pueraria was sown with a maize-cassava intercrop at the same season. In a 2-year cycle, 1 year of cropping was followed by 1 year fallow with pueraria for the cover crop-fallow system or with natural regrowth (mainly Chromolaena odorata) for the natural fallow system. Maize-cassava intercropping without a fallow period (continuous cropping) was included as a control. No fertilizer was applied throughout the experimental period. Pueraria produced 253 kg N ha -1 after the fallow period, compared with 109 kg N ha -1 for chromolaena; pueraria was also better in recycling P (11 kg P ha -1 ) than was chromolaena (9 kg P ha -1 ). Natural fallow for 1 year increased the maize yield from 75 to 350% from 1992 to 1996, and the cassava yield from 9 to 130% compared with continuous cropping. Cover crop-fallow resulted in a 22 to 72% higher maize yield than the natural fallow from 1992 to 1996. Although in 1992 and 1994 cassava tuber yield was lower with the cover crop-fallow than with the natural fallow, with better pueraria husbandry in 1996, cover crop-fallow increased the cassava tuber yield by 41%. With residue burning, the N balance was 27 kg N ha -1 yr -1 for the pueraria cover crop-fallow system and -15 kg N ha -1 yr -1 for the chromolaena natural fallow system. Cover crop-fallow maintained soil organic carbon status better than the natural fallow. Integration of a pueraria legume cover crop did not affect soil pH. Results indicate cover crop-fallow with pueraria could be a better alternative to traditional natural fallow under shortened fallow periods for raising or maintaining productivity of LAC soils of the humid tropics.

Nitrogen dynamics and crop growth on an alfisol and a vertisol under rainfed lowland rice-based cropping system

Crop rotation experiments were conducted over 2 years to quantify N supply-demand under rainfed lowland rice–chickpea and rice–fallow cropping systems on a loam Alfisol and a clay Vertisol in India. Significant differences among N rates (0, 40, 80, and 120 kg N ha −1) and soils were observed with rice for grain yield, total biomass and grain N uptake in both years. Low N response, low grain yield, low N uptake, and a short grain filling phase during the 1995 wet season was due to post-heading water stress. The stress was more pronounced on the Vertisol and at high N rates. This resulted in lower N content at maturity than at heading. The loss of biomass N from plant implied that apparent N recovery (AR) and physiological nitrogen use efficiency (PNUE) may differ significantly based on whether maximum N accumulation or total N uptake at maturity was used. Plant N recovery, both by the N difference method and 15 N technique, revealed much lower recovery of fertilizer N (21–27%) with rainfed lowland rice than with irrigated dry-season rice. The residual effect of N applied to the preceding rice crop was nonsignificant on all yield, growth, and N uptake parameters of chickpea. The performance of chickpea was better on the Alfisol than the Vertisol, principally due to soil physical attributes. The better performance and longer growth duration during 1994–1995 dry season as opposed to the 1995–1996 season was attributed to higher rainfall (92 mm versus 39 mm) and rainfall during the critical pod-filling to maturity phase. Mineralization and nitrification of N was negligible during the rice–fallow period due to the dry conditions and low organic matter content. This was corroborated by the similarities in N balance between rice–chickpea and rice–fallow system. The PNUE of rice was 33 to 57 kg grain per kg N absorbed compared with 25 to 27 kg grain per kg N absorbed of chickpea, owing mostly to higher N concentration of chickpea grain and the higher energy cost due to biological N fixation.

Ecosystem fertility and fallow function in the humid and subhumid tropics

The regeneration of natural vegetation (fallowing) is a traditional practice for restoring fertility of agricultural land in many parts in the tropics. As a result of increasing human population and insufficient fertilizer inputs, the ecosystem fertility functions of traditional fallows must now be improved upon via the use of managed fallows. Interactions between vegetation and soil determine nutrient losses and gains in crop—fallow systems and are influenced by fallow species, patterns and rates of biomass allocation, and crop and fallow management. Nutrient losses occur through offtake in crop harvests during the cropping phase and through leaching, runoff, and erosion in the cropping phase and the initial stage of fallows $#x2014; when nutrient availability exceeds nutrient demand by vegetation. Gains in nutrient stocks in later stages of fallow are generally more rapid on soils with high than low base status due to greater quantities of weatherable minerals and lack of constraints to N2 fixation, deep rooting, and retrieval of subsoil nutrients by fallow vegetation. On low base status soils (exchangeable Ca 5 yr) are needed for recovery of cation stocks and crop performance on low base status soils. On both soils, however, residual benefits of fallows on crop yields usually last less than three crops.

The uptake and use of nitrogen by paddy rice in fallow, cereal, and legume cropping systems

In a previous paper, we reported that prior crops either increased or decreased the yield of paddy rice (Oryza sativa L.) and altered its response to fertiliser N. We considered that rice yield responses to prior crop might have reflected the uptake of crop residue N and the efficiency of its use to produce grain. Experiments consisted of dry-season grain or legume crops, or fallow, followed by wet-season rice (cv. Lemont); and wet-season grain or legume crops, or fallow, followed by dry-season rice. Urea at one-third of the rate required for optimum rice yield was applied at 3 stages of rice crop growth: sowing, permanent flood, and/or panicle initiation. Soil N supplied 4.1 to 6.5 g N/m2 to the rice crop, depending on the season. Rice also recovered 0 to 0.25 of the N in the residue of a prior maize crop and 0.23 to 0.57 of the N in grain legume residues or a legume green manure crop; the fraction was greater if fertiliser N was not applied. Increased N uptake was the major contributor to heavier yield. The relationship between grain yield and crop N content was mostly linear, and thus physiological efficiency of N use for rice grain production was essentially constant across the range of environments provided by fertiliser N and cropping system treatments in this study. In experiments where fertiliser N was applied, there were small effects of prior cereal and legume cropping treatments on physiological efficiency. In contrast, without fertiliser N application, physiological efficiency was increased by prior cereal and legume crops, which likely resulted from a greater congruence between the N demand of the rice crop, and the N supply from the soil and incorporated residue, when compared with a fallow treatment.

Water storage in soils during the fallow: prediction of the effects of rainfall pattern and soil conditions in the Ebro valley of Spain

Fallowing remains a feature of dryland cereal agriculture in some low rainfall areas of central and northern Spain. To complement the limited number of measurements of water stored during the fallow, we developed a physically based simulation model to estimate the effects of variations in rainfall, soil characteristics and surface conditions on water storage in the profile. Mean annual rainfall in the locations investigated varied from ca. 300–500 mm and the mean amount of water stored during the last year of a bare fallow ranged from 1–48 mm, depending on soil and climate. The standard deviations of these amounts, each based on 25 simulations, varied from 11–39 mm. Rainfall in the last 3 months of the fallow was the principal cause of this year to year variation in storage. Surface stoniness and crop residues decreased evaporation from the soil and increased storage: there was very little drainage. These findings are consistent with measured water storage in soils in this part of Spain, and other areas of the world with similar climates and agricultural practices. Based on barley yield/rainfall regressions for data from a dry area in the Ebro valley, we estimated that the annual yields from a crop–fallow system would be 15% greater than those from annual cropping. For fallowing to be economic, yields per crop would need to be about twice those obtained with annual cropping. There may be yield benefits from fallowing apart from those resulting from extra water storage in the soil. Unless such benefits can be demonstrated, fallowing would appear to be uneconomical in this area of Spain.

Dryland Corn vs. Grain Sorghum in Western Kansas

Dryland crop yields in the U.S. Great Plains are limited by low precipitation and high potential evapotranspiration. In western Kansas wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] are grown commonly, whereas corn (Zea mays L.) is believed to lack sufficient drought and heat tolerance for dryland production. A study was conducted near Garden City, KS, from 1991 through 1995 to determine whether corn could be grown successfully. No-till (NT) and conventional-till (CT) corn and grain sorghum were compared. In the driest year, sorghum yielded 137% more than corn with CT and 85% more with NT, but in 3 of 5 yr, NT corn yielded from 34% to 112% more than NT sorghum. In the remaining year, CT sorghum yielded more than CT corn, but NT yields did not differ. Overall, NT increased corn yields by 28% and net return by 69%, but increased sorghum yields by only 11% and had no effect on net return. No-till corn yielded 28% more than NT sorghum and produced 169% more net return, whereas CT corn yielded 11% more than CT sorghum and produced 48% more net return. Dryland corn can be grown in western Kansas if lower yields and returns are accepted in dry years in exchange for yields and returns considerably higher than those of sorghum in favorable years. No tillage will substantially increase yields in most years and is essential to assure adequate corn yields in dry years.

Soil Organic Matter Pools during Early Adoption of Conservation Tillage in Northwestern Canada

AbstractChanges in soil organic matter (SOM) pools during adoption of reduced (RT) or zero tillage (ZT) can influence soil physical properties, nutrient cycling, and CO2 flux between soil and atmosphere. We determined soil organic C (SOC), soil microbial biomass C (SMBC), basal soil respiration (BSR), and mineralizable N to a depth of 200 mm at the end of 3, 5, and 6 yr after implementation of tillage management on a Falher clay (fine, montmorillonitic, frigid Typic Natriboralf) near Rycroft, Alberta, in a canola (Brassica campestris L.)‐wheat (Triticum Aestivum L.)‐barley (Hordeum vulgare L.)‐fallow cropping system. At the end of 6 yr, SOC was not different among tillage regimes and averaged 8.6 kg m−2. At the end of 3 and 5 yr, SMBC was not significantly different among tillage regimes, but at the end of 6 yr SMBC was 7% greater in RT and 9% greater in ZT than in conventional tillage (CT). Basal soil respiration and mineralizable N at the end of 6 yr were not different among tillage regimes following barley and averaged 2.7 g CO2‐C m−2 d−1 and 5.0 g inorganic N m−2 24 d−1, respectively. However, BSR following fallow was 2.2, 2.5, and 2.6 g CO2‐C m−2 d−1 in CT, RT, and ZT, respectively. Mineralizable N following fallow was 5.8 g inorganic N m−2 (24 d)−1 in RT and ZT and 7.3 g inorganic N m−2 (24 d)−1 in CT. At 0 to 50 mm, there was no significant increase in SOC at the end of 6 yr, a 17 to 36% increase in SMBC, and a 12 to 69% increase in BSR with ZT compared with CT, depending on rotation phase. Relatively small changes in SOM pools with adoption of conservation tillage may be attributable to the large amount of SOM initially present and the cold, semiarid climate that limits SOM turnover.

Economics of reduced tillage fallow-crop systems in the Dark Brown soil zone of Alberta

The use of conservation tillage management in fallow cropping systems reduces soil erosion and improves soil quality. The economic benefits of these alternate tillage methods are less certain. This study examined the economic returns from reduced tillage methods on fallow using yield and input data from two experiments at the Agriculture and Agri-Food Canada Research Centre at Lethbridge, Alberta. One experiment was long-term study initiated in 1955 with eight treatments, the second was a 5-yr study with 15 treatments. Results from the 5-yr study indicated no difference in net returns between conventional and reduced tillage fallow systems. In contras, the long-term study net returns were highest for tilled systems and lowest for herbicide-only systems. The long-term study had a build-up of weeds that are difficult to control with herbicides alone. The resulting lower average yield and higher herbicide costs of the herbicide-only treatments in the long-term study accounted for most of the contrasting results between the two experiments. An economic evaluation of tillage practices requires the entire system to be evaluated, not just the tillage component. Key words: Economics, tillage, reduced tillage, conservation practices, weed control

Water-Yield Relations of Several Spring-Planted Dryland Crops following Winter Wheat

A winter wheat (Triticum aestivum L.)-fallow cropping system has developed in the central Great Plains as a means to stabilize crop production in a highly variable climate. As an alternative, a flexibIe cropping system partially based on soil water at planting may allow producers to minimize risk while allowing some additional crop production during wetter climate cycles. Water-yield relations are critical in the development of flexible cropping systems. The experiment was conducted near Sidney, NE, on a Keith silt loam (fine silty, mixed mesic Aridic Argiustoll) to determine the response of five spring-planted crops (corn (Zea mays L.), grain sorghum [Sorghum bicolor (L.) Moench], pinto bean (Phaseolus vulgaris L.), proso millet (Panicum miliaceum L.), and sunflower (Helianthus annuus L.)) to three different soil water levels the year following winter wheat harvest. Water use of all crops increased with increasing soil water at planting. The grain yield of pinto bean and proso millet responded positively to soil water at planting. Soil water at planting accounted for less than half of the total variability in grain yield for corn, grain sorghum, and sunflower. Soil water at planting appears to be useful in determining the success of planting the two short duration crops (pinto bean and proso millet) the year after winter wheat harvest. For the long duration crops (corn, grain sorghum, and sunflower) other factors, such as precipitation near the time of flowering, may be more important in determining success

Modelling water, nitrogen, and crop yield for a long-term fallow management experiment

Two models that differ markedly in how they represent the crop-soil system have been used to simulate soil processes and crop production in the long-term experiment at Hermitage Research Station, Warwick, Queensland. The experiment was designed to examine the effects of tillage, stubble management, and nitrogen (N) fertiliser on the productivity of a winter cereal-summer fallow cropping system. it commenced in 1968 and the treatments have been maintained until the present. CENTURY operates on a monthly time step, considers all soil N transformations to occur in a single soil layer, and has a very simple crop growth routine that does not deal with crop phenology. APSIM provides a framework whereby a model of a cropping system is configured from component modules, which operate on a daily time step. For simulating the Hermitage experiment, modules to represent the dynamics of soil-water, N, surface residues, and growth of a wheat crop were used. The water and N modules deal with a multi-layered soil, whilst the wheat module develops leaf area, intercepts light, and accumulates and partitions dry matter in response to weather, soil-water, and N. Both models were specified to simulate the whole experimental period (1969-92) as a continuous run. The ability of these models to simulate grain yields, soil-water and drainage, nitrate-N, and soil organic matter were examined. Both models predict, in agreement with the observed data, that for this continuous cereal cropping system there has been a decline in soil organic matter for all the treatments and a reduction through time in the capacity of the soil to mineralise and accumulate nitrate during the fallows. CENTURY performed better than APSIM in predicting the relative yields of the N treatments but was less satisfactory than APSIM for absolute grain yield, soil-water, and drainage. Yield predictions with APSIM were sensitive to carry-over errors in the water balance from one season to the next, so that in some seasons large errors occurred in the predicted relative yields. Both models reproduced the observations well enough to indicate their suitability for providing useful insights into the behaviour of cropping systems where the focus is on depletion of soil fertility.

Nitrate Leaching in Dryland Agroecosystems as Influenced by Soil and Climate Gradients.

Farmers in dryland agriculture areas of the Central Great Plains have characteristically practiced alternate crop-fallow to stabilize yields. Large amounts of N released soon after sodbreaking and more recent fertilizer additions may have contributed to N movement below crop root zones. Improved water conservation techniques during fallow periods increases the possibility of NO3 leaching below root zones in modern-day crop-fallow systems. Soil topography and water supply may affect leaching potential. This study was conducted to test hypotheses regarding landscape position effects and potential evapotranspiration on depth of water and NO3 penetration. Three sites in eastern Colorado with equal annual precipitation, but with mean potential evapotranspiration varying from 1000 to 1900 mm yr-1 were evaluated. A soil catena was sampled at each site to test landscape effects. All sites were previously managed under tilled wheat-fallow systems for at least 50 yr. All summit (upland) sites had higher water and NO3 contents below their crop root zones than nearby native prairie sites. Soil water and NO3 content of soil profiles to a depth of 9 m were not related to slope position, but there was an inverse relationship between water and NO3 content of soil profiles and potential evapotranspiration. The total NO3 -N in cultivated profiles below the normal root zone of crops varied from 126 kg ha-1 at the northern site to 47 kg ha-1 at the southern site. Although some NO3 leaching had occurred, it did not appear to be a major problem for any particular landscape position or climatic zone on cultivated soils.

A METHOD OF ESTIMATING YIELD FOR LARGE-SCALE FIELD RESEARCH PROJECTS

The Innovative Acres field-scale project was designed to compare water-efficient farming systems with the more commonly used crop-fallow farming system in Saskatchewan. This project spanned the period between 1982 and 1987, and tested 40 locations each year. The present study was undertaken at two of these locations, to compare the sampling methodology used by the Innovative Acres (IA) project with a more intensive sampling scheme, and thereby assess the relative validity of productivity estimates developed from the IA sampling method. At both locations, grain yield estimates for the field based upon twelve IA benchmark sites were statistically similar (P > 0.05) to yield estimates from the more intensive sampling scheme (59 samples). Yield estimates from the IA transect more closely approximated the farmers' estimates of grain yield at both locations. Weighted grain yields, based on the distribution of topography along the transects, gave no better estimate of yield than did grouped mean data at both locations. The IA sampling procedure estimated to within 10% of the true mean grain yield, at the 90% probability level. It is concluded that this level of precision allows accurate comparisons to be made between two cropping systems. Key words: Field-scale research, transects, topography

Nitrogen Placement Evaluation for Winter Wheat in Three Fallow Tillage Systems

AbstractIncreased soil water storage with increasing amounts of surface residue in winter wheat (Triticum aestivum. L.)—fallow cropping systems has not consistently resulted in higher grain yields in the Great Plains. Earlier results had suggested increased amounts of surface residue may increase N immobilization and limit N availability, thereby reducing potential for use of the additional stored soil water. This study was conducted to determine if N placement below the zone of organic matter or surface residue accumulation would reduce N immobilization and increase yields. The effects of N placement were evaluated by surface broadcasting and injecting below the soil surface 15N depleted NH4NO3 at 45 kg ha−1 in no‐till, stubble mulch, and plow fallow method systems on an Alliance silt loam (fine‐silty, mixed mesic Aridic Argiustolls) in a long‐term study in western Nebraska. Dry matter and grain yield, N concentration, N uptake, 15N concentration, 15N uptake, and fertilizer recovery in plant tissue were determined for fallow method and N placement during the 1985, 1986, and 1987 growing seasons. Dry matter and grain yield, N concentration, N uptake, 15N uptake, and fertilizer recovery were all significantly affected by fallow method during all 3 yr of the study, being highest in plow and lowest in no‐till with stubble mulch values intermediate. Nitrogen placement, however, had no effect on any of the variables in any of the tillage systems. In this environment, N immobilization does not appear to be a factor limiting use of additional stored soil water in reduced tillage systems because fertilizer recovery was equal for both placement methods in all three tillage systems.

Dryland cropping strategies for efficient water-use to control saline seeps in the Northern Great Plains, U.S.A.

Investigations of the characteristics, hydrology, and causes of most saline seeps in the Northern Great Plains of the United States and Canada show that the same basic principles are involved in their development regardless of geographic location. Precipitation received in excess of the soil-root zone storage capacity, primarily during fallow or idle periods between crops, is the source of the water. One method of controlling saline seeps involves the establishment of a perennial deep-rooted crop, such as alfalfa ( Medicago sativa L.), on the recharge area for enough time to use existing and anticipated available-water supplies to maximum possible soil depth. Another method is to establish intensive, flexible cropping systems using adaptable crops in combination with proper soil, water and crop management practices to improve crop production-water use relationships sufficiently to reduce or eliminate the need for summer fallow. The key to developing more efficient cropping systems is to improve existing, and develop new, soil water conservation techniques to increase soil water storage during non-crop periods, thereby increasing the opportunity of developing cropping systems that use water more efficiently than conventional crop-fallow systems. This paper identifies and discusses the soil, water, and crop management strategies needed for the control of saline seeps. These strategies are based on the specific water requirements and rooting depths of crops, soil water conservation and storage, crop residue management, disease and weed control, and proper fertilization.

Population and agricultural intensity in the humid tropics.

A review of models of agricultural intensification and their application to the agricultural systems of the humid tropics is presented. Taken into account are the distributions of these systems at various population densities, available data on labor efficiencies, the costs of establishing continuous cropping, and data regarding soils under cultivation and various types of fallow. The findings that fallows much longer than 10 or 15 years serve no known agronomic function, that given preindustrial technology, grass fallows are disadvantageous, even environmentally destructive, and that continuous cropping usually entails a considerable amount of environmental modification support the interpretations that agricultural intensification in the humid tropics is best understood in terms of ecologically optimal strategies at different population densities. Points needing further investigation are highlighted: the reasons for very long fallows, and the comparative labor efficiencies of fallow and continuous cropping systems where crops and environments are similar.