Ha-1 Mm-1 Research Articles

Evapotranspiration and water-use efficiency of chilli crop (Capsicum annum L.) in arid environment

Lysimetric studies on chilli crop Capsicum annum L. cv. Haripur and Raipur) were conducted at Jodhpur during three kharif seasons viz., 2006, 2007 and 2008 to determine evapotranspiration requirements during different growth stages under three treatments of irrigation (viz., 100% potential evapotranspiration (PET), 50% of PET and control (10 irrigations each of 30 mm depth). The crop coefficients (ratio of evapotranspiration to reference evapotranspiration) were 0.38-0.47 at early growth stage, 0.39-0.69 at vegetative stage, 0.85-1.00 at flowering/fruit formation stages and 0.34-0.91 at fruit development/maturity stage with an average value of 0.62 for the entire season. The seasonal evapotranspiration for unstressed chilli crop (Irrigated @100%ET) was 620 mm in 2006, 548 mm in 2007 and 552 mm in 2008 with a mean of 573 mm. The highest dry fruit yield was obtained in 2008 due to the favourable weather conditions and least termite attack, resulting in highest water-use-efficiency of 1.84 kg of dry-fruit ha-1 mm-1 The water-use efficiency of chilli was highest (0.295-2.392 kg of dry-fruit ha-1 mm-) for the crop grown at 50%ET rate of irrigation.

English

In order to study the effect of different irrigation schedules on yield and water use of onion (Allium cepa L., cv. Alek and Kupusinski jabučar), a field experiment was conducted on the calcareous chernozem soil in the Institute of Field and Vegetable Crops, Novi Sad in Serbia during 2005, 2006 and 2007 growing seasons. The experiment was arranged in a randomized complete block design and adapted to conditions of sprinkling irrigation. Three irrigation treatments according to available soil water depletion (Т1 30, Т2 50 and Т3 70%) and a rainfed treatment (Т0) were included. Results showed that onion yield was significantly affected by irrigation. The highest onion bulb yields of 30.22 and 34.99 t ha-1 were obtained from treatment T1 and Т3, respectively, in 2005. However, the highest onion bulb yields of 38.46 and 40.07 t ha-1 were obtained from T2 and Т3 treatment in 2006 and 40.96 t ha-1 from T1 treatment in 2007, respectively. The lowest yield of 10.10 t ha-1 was obtained from T0 treatment in 2007 with limited precipitation and higher than average seasonal temperatures. The seasonal evapotranspiration values of irrigated (ETirr) and non irrigated (ETO) onions ranged from 435.6 to 542.9 mm and 290.2 to 393.9 mm, respectively. The highest and lowest water use efficiency (WUE) of 91.35 kg and 34.80 kg ha-1 mm-1 was obtained in irrigation and rainfed conditions in 2007, respectively. The highest irrigation water use efficiency (IWUE) of 280.54 kg ha-1 mm-1 was obtained from Т1 treatment in 2007, while the lowest value of 45.83 kg ha-1 mm-1 was obtained from T1 treatment during the rainy period of 2005. High yields of bulbs produced from treatments Т1, Т2 and Т3 in different years indicated that amount and distribution of precipitation seriously affected the soil water regime and irrigation schedule of onion in the region. Therefore, irrigation schedule of onion has to be adjusted to climatic conditions of each year, mostly to amount and distribution of precipitation.   Key words: Onion yield, irrigation scheduling, evapotranspiration, water use efficiency.

Viabilidade técnica e econômica da produção de ervilha (Pisum sativum L.) cultivada sob diferentes lâminas de irrigação

Realizou-se, com o presente trabalho, uma avaliação técnica e econômica da produção de ervilha (Pisum satiums L.) em função de lâminas de irrigação. O experimento foi instalado em casa de vegetação, com delineamento inteiramente casualizado (DIC), com cinco tratamentos de reposição de água no solo (50; 75; 100; 125 e 150% da capacidade de campo) e quatro repetições. O momento de irrigar foi definido quando a tensão média da água no solo, obtida nos tensiômetros instalados na parcela com 100% de reposição de água, atingiu 15 kPa. Concluiu-se que a produção da cultura e o número de vagens por planta foram afetados pelo déficit e pelo excesso hídrico aplicados pelos tratamentos. A máxima produtividade obtida foi igual a 4.197 kg ha-1 com a aplicação de 188,4 mm de água, e a lâmina ótima econômica foi estimada em 187,4 mm; a eficiência no uso da água máxima foi de 27,23 kg ha¹ mm-1, para uma lâmina de 86,25 mm.

Chickpea water use efficiency in relation to cropping system, cultivar, soil nitrogen and Rhizobial inoculation in semiarid environments

Crops grown in semiarid rainfed conditions are prone to water stress which could be alleviated by improving cultural practices. This study determined the effect of cropping system, cultivar, soil nitrogen status and Rhizobium inoculation (Rz) on water use and water use efficiency (WUE) of chickpea (Cicer arietinum L.) in semiarid environments. The cultivars Amit, CDC Anna, CDC Frontier, and CDC Xena were grown in no-till barley, no-till wheat, and tilled-fallow systems and under various rates of N fertilizer (0, 28, 56, 84, and 112 kg N ha-1) coupled with or without Rz. The study was conducted at Swift Current and Shaunavon, Saskatchewan, from 2004 to 2006. On average, chickpea used about 10 mm of water from the top 0�15 cm soil depth. In the tilled-fallow system, chickpea extracted 20% more water in the 15�30 cm depth, 70% more in the 30�60 cm depth, and 156% more in the 60�120 cm depth than when it was grown in the no-till systems. CDC Xena had WUE of 5.3 kg ha-1 mm-1 or 20% less than the average WUE (6.6 kg ha-1 mm-1) of the three other cultivars, even though these cultivars used the same amounts of water. Water use efficiency increased from 4.7 to 6.8 kg ha-1 mm-1 as N fertilizer rate was increased from 0 to 112 kg N ha-1 when chickpea was grown in the no-till barley or wheat systems, but chickpea grown in the tilled-fallow system did not respond to changes in the fertilizer N rates averaging WUE of 6.5 kg ha-1 mm-1. In the absence of N fertilizer, the application of Rz increased WUE by 33% for chickpea grown in the no-till barley system, 30% in the no-till wheat system, and 9% in the tilled-fallow system. Chickpea inoculated with Rhizobium achieved a WUE value similar to the crop fertilized at 84 kg N ha-1. Without the use of Rz, chickpea increased WUE in a linear fashion with increasing fertilizer N rates from 0 to 84 kg N ha-1. Cropping system, cultivar, and inoculation all had greater impact on WUE than on the amount of water extracted by the crop from the soil. The improvement of cultural practices to promote general plant health along with the development of cultivars with improved crop yields will be keys for improving water use efficiency of chickpea in semiarid environments

Nutrient management adaptation for dryland maize yields and water use efficiency to long-term rainfall variability in China

Rainfed crop production in northern China is constrained by low and variable rainfall, and by improper management practices. This study explored both the impact of long-term rainfall variability and the long-term effects of various combinations of maize stover, cattle manure and mineral fertiliser (NP) applications on maize (Zea mays L.) yields and water use efficiency (WUE) under reduced tillage practices, at Shouyang Dryland Farming Experimental Station in northern China from 1993 onwards. The experiment was set up according to an incomplete, optimal design, with 3 factors at five levels and 12 treatments including a control with two replications. Grain yields were greatly influenced by the amount of rain during the growing season, and by soil water at sowing. Annual mean grain yields ranged from 3 to 10 t ha-1 and treatment mean yields from 4.2 to 7.2 t ha-1. The WUE ranged from 40 in treatments with balanced nutrient inputs in dry (weather/or soil) years to 6.5 kg ha-1 mm-1 for the control treatments in wet years. The WUE averaged over the 15-year period ranged from 11 to 19 kg ha-1 mm-1. Balanced combination of stover (3000�6000 kg), manure (1500�6000 kg) and N fertiliser (105 kg) gave the highest yield and hence WUE. It is suggested that 100 kg N per ha should be a best choice, to be adapted according to availability of stover and manure. Possible management options under variable rainfall conditions to alleviate occurring moisture stress for crops must be tailored to the rainfall pattern. The potentials of split applications, targeted to the need of the growing crop (response nutrient management), should be explored to further improve grain yield and WUE

Effects of irrigation regimes on yield and water productivity of safflower (Carthamus tinctorius L.) under Mediterranean climatic conditions

A field study was carried out in order to determine the effect of deficit irrigation regimes on grain yield and seasonal evapotranspiration of safflower (Carthamus tinctorius L.) in Thrace Region of Turkey. The field trials were conducted on a loam Entisol soil, on Dincer, the most popular variety in the research area. A randomised complete block design with three replications was used. Combination of four well-known growth stages of the plant, namely vegetative (Va), late vegetative (Vb), flowering (F) and yield formation (Y) were considered to form a total of 16 (including rain fed) irrigation treatments. The effect of irrigation and water stress at any stage of development on grain yield per hectare and 1000 kernels weight was evaluated. Results showed that safflower was significantly affected by water stress during the sensitive late vegetative stage. The highest yield was obtained in VaVbFY treatment. Seasonal irrigation water use and evapotranspiration were 501 and 721 mm, respectively, for the non-stressed treatment. Safflower grain yield of this treatment was 5.22 Mg ha-1 and weight of 1000 kernels was 55 g. The seasonal yield�water response factor value was 0.87. The total water use efficiency was 7.2 kg ha-1 mm-1. Irrigation schedule of the non-stressed treatment may be as follows: the first irrigation is at the vegetative stage, when after 40�50 days from sowing/elongation and branching stage, that is the end of May; the second irrigation is at the late vegetative stage, after 70�80 days from sowing/heading stage, that is in the middle of June; the third irrigation is at the flowering stage, approximately 50% level, that is the first half of July; and the fourth irrigation is at the yield formation stage, seed filling, that is the last week of July.

Micro-meteorological variations and Rain water-use efficiency of a Silvi-pastoral system

The solar radiation disposition, soil moisture depletion pattern and rain water-use efficiency of a silvi-pastoral system at Jodhpur were studied during 2000 to 2003. Factorial combination of a pasture viz., Cenchrus ciliaris and a fodder shrub viz., Colophospermum mopane and with two trees viz., Hardwickia binata and Prosopis cineraria at two levels of nitrogen (No and N20) were tried. The intercepted insolation varied from 54 to 80% depending upon the leaf area index (0.65-1.40). The albedo varied from 20.3 to 24.4%. Soil moisture depletion was more in all fertilized than unfertilized plots of legume, grass and tree combination treatments. The rain water-use efficiency (WUE) was higher in fertilized plots of C. ciliaris (3.37-14.05 kg DM ha-1 mm-1) compared to unfertilized plots (2.65-9.71 kg DM ha-1 mm- 1) and it was highest in combination of grass and legume compared to sole components.

Water use efficiency and water and nitrate distribution in soil in the semiarid prairie: Effect of crop type over 21 years

In the semiarid prairie, available water is the most limiting and nitrogen the second most limiting factor influencing crop production. Although numerous studies have been conducted on the effect of management practices on water use efficiency (WUE), most have concentrated on monoculture wheat, the major crop grown in the region. Even those studies dealing with other crop types have mostly been short-term in nature. But precipitation is so variable in amount and distribution that such an assessment is best conducted in long-term experiments. We used the results of a 21-yr experiment, conducted in the Brown soil zone at Swift Current, Saskatchewan, to determine the influence of crop type on WUE, and used the distribution of water and NO3-N in the soil, and N uptake by the crop to assist in interpreting these results. Four crop rotations were compared: summer fallow-wheat-wheat (F-W-W), F-flax-W (F-Flx-W), continuous wheat (Cont W) and wheat-lentil (W-Lent). All received N and P fertilizer based on soil test. In the following presentation, the rotation phase shown in parentheses was the phase referred to. We used water and NO3-N measured in consecutive 0.3-m depth segments to 1.2 m in the soil, taken just prior to seeding and after harvest, and precipitation, to make this assessment. About 10 mm more water was conserved in the F-W-W rotation than in the F-Flx-W system during the 21-mo summer fallow period, and most of this difference in water was located in the 0.3- to 0.9-m depth. Soil water in the profile was 14 mm greater following flax harvest than following wheat harvest (mostly located in 0.6- to 1.2-m depth), because flax produces less biomass and has shorter roots than wheat. At harvest, wheat dried the soil to near the wilting point (154 mm), but flax and lentil left about 10 mm of available water in the profile (mostly in the 0.6- to 1.2-m depth), suggesting shallower rooting depths. Over the 9-mo winter period about 58 mm of water was stored in the soil after wheat and 41 mm after flax. Wheat stubble conserved more overwinter water than flax stubble because of its taller height. Lentil, with its much shorter stubble, conserved about 7 mm less water than wheat during winter. Because flax produces much less biomass and withdraws less N from the soil than wheat, it left more NO3-N in the soil (27 kg ha-1 more at seeding and 23 kg ha-1 more at harvest); most of the extra NO3 was in the 0.3- to 1.2-m depth reflecting flax's shallower roots. During the 9-mo overwinter period, 16 kg ha-1 of NO3-N was mineralized following wheat and 33 kg ha-1 following flax. In the spring, Cont W and stubble wheat in F-W-(W) had about 50% as much soil NO3-N as the W-Lent rotation, reflecting the cumulative benefits of N2 fixation by the pulse crop over the years . By harvest, soil NO3-N under (W)-Lent > W-(Lent) > F-Flx-(W) > F-W-(W) > Cont W. The excess NO3-N in the (W)-Lent compared to W-(Lent) was located in the 0- to 0.6-m depth suggesting excessive fertilizer application to the wheat phase of this rotation and implying a need for agronomists to reassess the criteria used for N recommendations for rotations containing pulse crops. Lentil used as much water as wheat even though its biomass was much less. WUE for wheat grown on summer fallow averaged 8.11 kg ha -1 mm-1, and for wheat grown on stubble 6.9 kg ha-1 mm-1. WUE for wheat was also higher when it followed flax than when it followed wheat. The WUE of flax and lentil averaged 50% and 64%, respectively, of wheat following wheat. A more meaningful way of expressing the efficiency of water use is as precipitation required per unit of produce from the complete cropping system (PUE). The PUE increased with cropping intensity on a yield basis (kg ha-1 mm-1): Cont W (4.6) > W-Lent (4.2) > F-W-W (4.1) > F-Flx-W (2.9) (opposite response to WUE). When PUE was calculated on a dollars produced per rotation basis ($ ha-1 mm-1): W-Lent (1.0) was higher than the other three rotations (0.6 to 0.7). Key words: Soil water, soil nitrate, lentil, flax, wheat, crop rotation, precipitation use efficiency

Water use of pulse crops at various plant densities under fallow and stubble conditions in a semiarid environment

Understanding water use characteristics of crops is essential for optimizing crop productivity in semiarid environments. This study determined water use (WU), water use efficiency (WUE), and postharvest residual soil water (PHRSW) of dry pea (Pisum sativum L.) and desi and kabuli chickpea (Cicer arietinum L.) at four plant densities under fallow and stubble cropping systems in a semiarid environment. Crops were grown in southwest Saskatchewan from 1998 to 2000. Chickpea used 28% more water than dry pea, while kabuli chickpea used 14% more water than desi chickpea only when grown on fallow at one of the sites. Pulses grown on fallow used 66% more water than when grown on stubble, with largest difference (48%) in WU between the two cropping systems being in the 60- to 90-cm soil depths. Overall, dry pea had the greatest WUE (12.9 kg ha-1 mm-1), followed by desi chickpea (7.3 kg ha-1 mm-1) and kabuli chickpea (6.6 kg ha-1 mm-1). Water use efficiency increased with increasing plant density for all the pulses, with dry pea showing a stronger response than chickpea. The PHRSW below the 60-cm depth differed significantly among pulses. Dry pea left an average of 33 mm available water at harvest, the desi left 20 mm, and the kabuli 13 mm. A deeper rooting crop grown after dry pea may benefit more from water conservation in the soil profile than when grown after chickpea under semiarid environmental conditions. Key words: Cicer arietinum, Pisum sativum, water use efficiency, rooting depth

Effects of Soil Clay Content on Water Balance and Productivity in Rainfed Lowland Rice Ecosystem in Northeast Thailand

Water availability is one of the determinants of productivity of rainfed lowland rice (Oryza sativa L.). Quantifying water losses from a paddy field, such as deep percolation and lateral seepage, assists estimation of water availability to the rice crop and development of appropriate water management in the lowlands. The main objective of this study was to evaluate paddy water availability and productivity across various soils in Northeast Thailand. The daily rate of downward water flow from standing water in the field (D) varied between 0 and 3 mm day-1 from clayey to sandy soils when the standing water was connected to groundwater table. However, when the standing water was separated from groundwater table, D increased up to 5 mm day-1 on soils with very low clay content in the topsoil. Daily net lateral water flow from the field (L) averaged over the season varied between 5 and 24 mm day-1 for the outflow and between 3 and 16 mm day-1 for the inflow. Both the inflow and outflow tended to be associated negatively with the soil clay content. The seasonal water loss through D plus L during the growing season in the lowlands was also negatively related to the soil clay content. The yield of a major rainfed lowland rice cultivar in Northeast Thailand (KDML105) varied from 2 to 4 t ha-1 across the region, and the water productivity (the ratio of grain yield to cumulative rainfall from transplanting/seedling establishment to maturity) ranged from 3 to 9 kg ha-1 mm-1. High clay soils could provide good standing water until late in the growing season, so the high production efficiency was measured on such soils.

Função de resposta do meloeiro a diferentes lâminas de irrigação e doses de nitrogênio

Objetivou-se estudar o efeito de lâminas de irrigação e doses de nitrogênio sobre o rendimento físico e econômico do meloeiro. O experimento foi conduzido em Pentecoste-CE, entre setembro e dezembro de 2002, em um delineamento experimental em blocos ao acaso no esquema de parcelas subdivididas. Os tratamentos constituíram-se da combinação entre quatro lâminas de irrigação (W1= 232,7; W2= 334,7; W3= 422,1; W4= 567,8 mm) e quatro níveis de adubação nitrogenada (N0= 0; N1= 75; N2= 150; N3= 300 kg ha-1), com quatro repetições. Foram avaliados dez modelos estatíticos e o que melhor se ajustou aos dados do experimento foi o polinomial quadrático, sem intercepto e sem interação entre os fatores lâminas de água (W) e doses de nitrogênio(N), conforme a equação de função de produção Y= 70,77509 W+34,16737 N0,05781 W²0,07612 N². Verificou-se que o fator água apresentou efeito significativo sobre o rendimento do meloeiro, enquanto o fator nitrogênio foi significativo apenas ao nível de 6,43%. Não houve interação significativa entre os fatores lâmina de irrigação e doses de nitrogênio. O máximo rendimento estimado foi de 25.496,1 kg ha-1. A receita líquida máxima estimada foi de R$3.353,24 ha-1 obtida com rendimento de 25.384,3 kg ha-1 de melão, utilizando-se 609,2 mm de água e 186,2 kg ha-1 de nitrogênio. A ótima eficiência econômica do uso da água estimada foi de 41,66 kg ha-1 mm-1, para uma dose de 186,2 kg ha-¹ de nitrogênio.

Effects of regulated deficit irrigation on grain yield and water use efficiency of spring wheat in an arid environment

Grain yield and water use efficiency (WUE) of spring wheat ( Triticum aestivum L.) in arid environments can be improved by applying irrigation selectively to allow soil water deficits to develop at non-critical stages of crop development. Field experiments were conducted on a loam soil in Zhangye district, northwest China in 2003 and 2004 to determine the grain yield, yield components, and water use characteristics of spring wheat in response to regulated deficit irrigation (RDI) schemes. Wheat grown under the RDI schemes produced 17% (in 2004) and 29% (in 2003) higher grain yield than wheat grown under water deficit-free control (5.6 t ha-1 in 2003 and 6.2 t ha-1 in 2004). Among six RDI schemes studied, wheat having a high water deficit at the jointing stage, but free from water def icit from booting to grain-filling produced highest grain yield in both 2003 (7.95 t ha-1) and 2004 (7.26 t ha-1). Compared with the control, wheat plants grown under the RDI schemes received 59 mm (or 15%) less water via irrigation, but they either extrac ted 41 mm more (or 74%) water from the soil profile (in 2003) or lowered (16%) evapotranspiration (ET) (in 2004). Grain yield increased as ET increased from 415 to 460 mm, and declined beyond 460 mm. The WUE values varied from 0.0116 to 0.0168 t ha-1 mm-1, and wheat grown under the RDI had 26% greater WUE compared with the control. Grain yield and WUE of spring wheat can be greatly improved by regulated deficit irrigation with reduced amounts of water. This practice is particularly valuable in arid regions where wheat production relies heavily on irrigation. Key words:

Comportamento da alface tipo americana sob diferentes tensões da água no solo, em ambiente protegido

Visando a definir critérios para o manejo da irrigação para alface tipo americana, cv. Raider, esse trabalho foi desenvolvido para avaliar o efeito de diferentes tensões da água no solo sobre o comportamento produtivo da cultura, em ambiente protegido, na região de Lavras - MG. O experimento foi instalado em casa de vegetação com delineamento em blocos casualizados, tendo quatro repetições. Os tratamentos foram constituídos de seis tensões de água no solo como indicativas do momento de irrigar. As tensões preestabelecidas foram 15; 30; 45; 60; 75 e 90 kPa, à profundidade de 0,15 m. Os resultados permitiram concluir que, no emprego de tensões em torno de 15 kPa, há tendência em obter plantas mais altas, com maior peso de matéria fresca comercial e menor teor de matéria seca da parte comercial. Também foi possível observar melhor eficiência no uso da água (469,22 kg ha-1 mm-1) sob tensão de 15 kPa.

Erosão hídrica em um Nitossolo Háplico submetido a diferentes sistemas de manejo sob chuva simulada. II - Perdas de nutrientes e carbono orgânico

Com a erosão hídrica, há o transporte de nutrientes para fora das lavouras e, com isso, pode ocorrer o empobrecimento dos solos e a contaminação do ambiente fora do local da erosão. Utilizando um simulador de chuvas de braços rotativos, foram aplicadas, no campo, três chuvas simuladas no cultivo do milho e três no de feijão, com intensidade constante de 64 mm h-1 e energia cinética de 0,2083 MJ ha-1 mm-1 , no Planalto Sul Catarinense, entre março de 2001 e abril de 2003, para avaliar as perdas de nutrientes e carbono orgânico (CO) pela erosão hídrica sobre os seguintes tratamentos de manejo do solo, em duas repetições: solo sem cultivo com uma aração + duas gradagens (SSC); cultivos de milho e feijão com uma aração + duas gradagens sobre resíduos dessecados (PCO); cultivos de milho e feijão em semeadura direta sobre resíduos dessecados em solo previamente preparado (SDI); cultivos de milho e feijão em semeadura direta sobre resíduos dessecados em solo nunca preparado (SDD), cultivos de milho e feijão em semeadura direta sobre resíduos queimados em solo nunca preparado (SDQ); e solo sem cultivo com campo nativo melhorado (CNM). Utilizou-se um Nitossolo Háplico alumínico argiloso, com inclinação média do terreno de 0,165 m m-1. As concentrações dos nutrientes e do CO nos sedimentos transportados por erosão foram maiores nos preparos conservacionistas do que nos convencionais, enquanto as perdas totais comportaram-se de maneira inversa. Na água da enxurrada, as concentrações e as perdas de NH4+ e NO3- diminuíram do cultivo do milho para o do feijão, enquanto as de P aumentaram. No caso do K, ocorreu redução da concentração e aumento das perdas. As taxas de empobrecimento do solo situaram-se, em geral, próximas de um para os nutrientes e para o CO. As concentrações dos nutrientes e do CO nos sedimentos transportados correlacionaram-se, linear e positivamente, com a composição química da camada de 0-0,025 m de profundidade do solo de onde o sedimento foi removido.

Evapotranspiration efficiency of pea in south and central Alberta

Evapotranspiration (ET) efficiency regulates suitability and management of crops on the Canadian prairies. To evaluate the ET efficiency of pea (Pisum sativum L.), soil water depletion and yields as a function of precipitation were determined for Carneval pea at 28 sites in south and central Alberta from 1995 to 1998. Soil water depletion between seeding and harvest was as high as 112 mm at sites with high levels of available soil water at seeding and low to moderate levels of precipitation. Pea was capable of extracting soil water to a depth of about 0.6 m at most sites, but extraction of soil water below this depth was much more variable. At sites where soil water did not limit the depth of soil water extraction, a negative correlation was observed between the maximum depth of effective soil water extraction and the sum of maximum temperature degree-days above 25.6°C. The ET efficiency of pea seed yield ranged from 7.5 to 19.1 kg ha-1 mm-1, with an average value of 13.0 kg ha-1 mm-1. No correlation was observed between ET efficiency and weather variables, such as average temperature, vapor pressure deficit or length of the growing season. Key words: Pisum sativum, water use efficiency, root depth, drought stress

Cropping frequency, wheat classes and flexible rotations: Effects on production, nitrogen economy, and water use in a Brown Chernozem

Producers in the semiarid Canadian prairies rely on frequent summerfallowing (F) to conserve water, control weed infestations, and maximize soil mineral N reserves, but this practice often results in soil degradation. A crop rotation experiment was initiated in 1987 on a medium-textured, Orthic Brown Chernozem at Swift Current, Saskatchewan, to determine the most ideal cropping frequency for wheat in this region and whether a fixed rotation such as fallow-wheat (Triticum aestivum L.) - wheat (F-W-W) or F-W-W-W would be more effective than flexible rotations in which fallowing is decided each spring based on criteria such as available soil water (if water), or the need to control perennial weed infestations (if weeds). The study also compared the production of traditional Canada Western Red Spring (CWRS) wheat class with the newer higher-yielding (Hy), Canada Prairie Spring (CPS) wheat class. We analyzed results of six rotations over the first 12 yr of the study. The rotations included F-W-W, F-W-W-W, F-Hy-Hy, Continuous wheat (Cont W), Cont W (if weeds), and Cont W (if water). Reduced tillage management was used and stubble was cut tall to enhance snowtrap. Fertilizer N was applied based on soil tests and fertilizer P was applied based on the general recommendations for the region. Over the 1988–1999 period, weather conditions were generally favourable and yields were above average for this region. Canada Prairie Spring wheat outyielded CWRS by 32% when grown on fallow and by 17% when grown on stubble; however, straw yields of the two wheat classes were similar on fallow and CPS was 11% less than CWRS on stubble. Harvest index (HI) averaged 44% for CPS and 37% for CWRS wheat. Water use efficiency for CWRS wheat grown on fallow averaged 7.2 kg ha-1 mm-1 and for CPS 9.4; when grown on stubble the respective values were 6.3 and 7.5 kg ha-1 mm-1. Grain N concentration for CWRS was slightly higher for wheat grown on fallow (25.7 g kg-1) than on stubble (24.5 g kg-1), but was similar for CPS wheat on grown on fallow and stubble (21.9 g kg-1). Straw N concentration averaged 3.8 g kg-1 for CWRS and 4.4 g kg-1 for CPS. Nitrogen yield for grain from CPS was 9% greater than from CWRS when grown on fallow, but there was no effect of wheat class when grown on stubble. Nitrogen yield of CPS straw was 15% greater than for CWRS when grown on fallow, but on stubble N yield was generally not affected by wheat class. Nitrogen harvest index (NHI) averaged about 80% for both wheat classes, whether grown on fallow or stubble. On a rotation basis, grain produced with F-W-W was 1502 kg ha-1 yr-1. The F-W-W-W and Cont W (if weeds) rotations produced 9% more grain than F-W-W, while Cont W (if water) produced 24% more, F-Hy-Hy produced 26% more, and Cont W produced 30% more than F-W-W. Nitrogen production in the grain, straw and aboveground plant material was lowest in F-W-W, highest in Cont W, and intermediate for other rotations. Although the economic and soil quality assessments have yet to be completed, a preliminary conclusion based on crop production characteristics alone suggests that a flexible cropping system in which available soil water in spring is used as the determining criterion is superior to a fixed F-W-W or F-W-W-W rotation. Key words: Yield, N concentration, N yield, water deficit, wheat classes, regressions

Fire and the dynamics of semi-arid grassland: influence on plant survival, productivity and water-use efficiency

There is a lack of knowledge concerning the effect of fire behaviour on the vegetation dynamics of semi-arid climates. Arising from this, an investigation was initiated to characterise the behaviour of fires burning with the wind (head fire) and against the wind (back fire). The behaviour of these fires was related to the response of the vegetation by monitoring the recovery and productivity of the grass sward after only one burn over a two year period (2000/01 to 2001/02 seasons). The results showed that head fires had significantly greater flame height and rate of spread than back fires. However, at ground level back fires were more intense and had a negative effect on recovery of the grasses, resulting in lower litter, yield and water-use efficiency (aboveground phytomass or crude protein produced per unit of evapotranspiration). Fire had a significant effect on plant density and cover, with basal cover 68% lower than that of unburnt grassland two months after the fire. Cymbopogon plurinodis with large tufts had the most die-back of all the species. With the exception of plant cover and density, which takes longer to recover, it takes approximately two complete growing seasons to recover from most of the detrimental effects of fire. The initial increased crude protein content of the plant material caused by fire did not off set the approximately 50% reduction in plant production the first growing season after the fire. Fire significantly decreased WUE (water-use efficiency), with an average over the two growing seasons of 3.06kg ha-1 mm-1 and 2.45kg ha-1 mm-1 for unburnt and burnt grassland respectively. In various semi-arid grassland areas, the use of fire as a management tool is questionable if there is no specific purpose for it.

Eficiência da irrigação em rendimento de grãos e matéria seca de milho

O objetivo deste trabalho foi avaliar a eficiência da irrigação e o efeito do déficit hídrico sobre o rendimento de grãos e o acúmulo de matéria seca da parte aérea de uma cultura de milho. O experimento foi conduzido na Universidade Federal do Rio Grande do Sul, em Eldorado do Sul, RS, durante quatro anos agrícolas, de 1993/94 a 1996/97. Utilizando um delineamento experimental em faixas com aspersores em linha, foram aplicados cinco níveis de irrigação, da capacidade de campo à ausência de irrigação. Os rendimentos de grãos foram crescentes com aumentos no nível de irrigação até 80% da dose necessária para a capacidade de campo; a máxima eficiência da irrigação foi obtida entre 60 e 80% e esteve associada a déficits hídricos durante o período crítico da cultura, alcançando 40 kg ha-1 mm-1. Por outro lado, a maior eficiência da irrigação para produção de matéria seca da parte aérea foi obtida com déficits hídricos prolongados durante o período de crescimento exponencial da cultura. Reduções no rendimento de grãos, causadas por déficit hídrico, estiveram relacionadas com a redução do número de grãos por espiga e por metro quadrado, já que o peso médio de grãos não foi afetado.

Water-use efficiency and transpiration efficiency of wheat under rain-fed conditions and supplemental irrigation in a Mediterranean-type environment

Growth and water use were measured in wheat (Triticum aestivum L.) grown in northern Syria in a typical Mediterranean climate over five seasons 1991/92–1995/96. Water use was partitioned into transpiration (T) and soil evaporation (Es) using Ritchie's model, and water-use efficiency (WUE) and transpiration efficiency (TE) were calculated. The aim of the study was to examine the influence of irrigation and nitrogen on water use, WUE and TE. By addition of 100 kg N ha-1, Es was reduced from 120 mm to 101 mm under rain-fed conditions and from 143 mm to 110 mm under irrigated conditions, and T was increased from 153 mm to 193 mm under rain-fed conditions and from 215 mm to 310 mm under irrigated conditions. Under rain-fed conditions, about 35% of evapotranspiration (ET) may be lost from the soil surface for the fertilized crops and 44% of ET for the unfertilized crops. Transpiration accounted for 65% of ET for the fertilized crops and 56% for the unfertilized crops under rain-fed. As a result of this, WUE was increased by 44% for dry matter and 29% for grain yield under rain-fed conditions, and by 60% for dry matter and 57% for grain yield under irrigated conditions. Transpiration efficiency for the fertilized crops was 43.8 kg ha-1 mm-1 for dry matter and 15 kg ha-1 mm-1 for grain yield, while TE for the unfertilized crops was 33.6 kg ha-1 mm-1 and 12.2 kg ha-1 mm-1 for dry matter and grain yield, respectively. Supplemental irrigation significantly increased post-anthesis water use, transpiration, dry matter and grain yield. Water-use efficiency for grain yield was increased from 9.7 to 11.0 kg ha-1 mm-1 by supplemental irrigation, although WUE for dry matter was not affected by it. Irrigation did not affect transpiration efficiency for grain yield, but decreased transpiration efficiency for dry matter by 16%. This was associated with higher harvest index as a result of good water supply in the post-anthesis period and increased transpiration under irrigated conditions.

Temporal variation in aboveground biomass ofLeymus chinense steppe from species to community levels in the Xilin River Basin, Inner Mongolia, China

We analyzed the long-term dynamics of aboveground biomass ofLeymus chinense steppe in relation to interannual variation of precipitation and temperature during 1980–1989 at levels of community, growth form and species in the Xilin river basin, Inner Mongolia Autonomous Region, China. Annual aboveground net primary production (ANPP) varied from 154.00 g m-2 yr-1 in 1980 to 318.59 g m-2 yr-1 in 1988, with a mean of 248.63 g m-2 yr-1 and the coefficient of variation of 25%. ANPP was not significantly correlated to annual precipitation and total precipitation during April–September atp≤0.05 level, but precipitation in May and August accounted for 69% of interannual variation of ANPP. The means of rain use efficiency and water use efficiency ofL. chinense steppe were 8.1 kg DM ha-1 mm-1 yr-1 and 0.89 mg DM g-1 H2O respectively. Aboveground biomass of various growth forms and species had different response patterns to interannual variation of precipitation and temperature. Monthly and seasonal distribution of precipitation and temperature were the key controls of aboveground biomass of species.