Effect of nitrogen supply on crop conductance,water- and radiation-use efficiency of wheat

Water-use efficiency (WUE_DM) is directly related to radiation-use efficiency (RUE) and inversely related to crop conductance (g_c). We propose that reduced WUE_DM caused by shortage of nitrogen results from a reduction in RUE proportionally greater than the fall in conductance. This hypothesis was tested in irrigated wheat crops grown with contrasting nitrogen supply; treatments were 0, 80 and 120 kg N ha⁻¹ in 1998 and 0, 80, 120 and 160 kg N ha⁻¹ in 1999. We measured shoot dry matter, yield, intercepted solar radiation and soil water balance components. From these measurements, we derived actual evapotranspiration (ET), soil evaporation and transpiration, WUE_DM (slope of the regression between dry matter and ET), WUE_Y (ratio between grain yield and ET), RUE (slope of the regression between dry matter and intercepted radiation), and g_c (slope of the regression between transpiration and intercepted radiation). Yield increased from 2.3 in unfertilised to an average 4.7 t ha⁻¹ in fertilised crops, seasonal ET from 311 to 387 mm, WUE_DM from 23 to 37 kg ha⁻¹ mm⁻¹, WUE_Y from 7.6 to 12.4 kg ha⁻¹ mm⁻¹, RUE from 0.85 to 1.07 g MJ⁻¹, while the fraction of ET accounted for soil evaporation decreased from 0.20 to 0.11. In agreement with our hypothesis, RUE accounted for 60% of the variation in WUE_DM, whereas crop conductance was largely unaffected by nitrogen supply. A greater fraction of evapotranspiration lost as soil evaporation also contributed to the lower WUE_DM of unfertilised crops.     

Effect of irrigation frequency and amount on water use efficiency and yield of sesame (Sesamum indicum L.) under field conditions

The water-use characteristics of sesame (Sesamum indicum L.) were studied in the field under furrow irrigation. Irrigation water quantities were based on pan evaporation (E_pan) from a screened class-A pan. Treatments consisted of three irrigation intervals (I₁: 7 days; I₂: 14 days, I₃: 21 days), and four pan coefficients (K_cp 1: 0.60; K_cp 2: 0.80, K_cp 3: 1.00 and K_cp 4: 1.20). Average irrigation values for each treatment varied from 467 to 857 mm in 2003 and 398 to 654 mm in 2004. The highest seasonal evapotranspiration was obtained from the I₃K_cp 4 treatment in 2004 (1019 mm); the lowest value was observed in the I₁K_cp 1 treatment in the same year (598.0 mm). Data collected in 2003 and 2004 showed that the amount of irrigation water applied significantly the affected seed yield. However, the effects of irrigation interval on yield were not significant. On average, the K_cp 3 treatment gave the highest seed yield (1.915 t ha⁻¹), whereas K_cp 1 treatment gave the lowest (1.538 t ha⁻¹). Seasonal yield response factors (k_y) were 1.01 and 0.54 in 2003 and 2004, respectively. ET/E_pan ratios for each treatment varied from 0.3 to 1.3 in 2003 and from 0.1 to 1.1 in 2004. In conclusion, the K_cp 3 plant-pan coefficient is recommended for sesame grown under field conditions in order to maximise yield.     

Estimated evapotranspiration of rice based on pan evaporation as a surrogate to lysimeter measurement

Reference crop evapotranspiration (ET _o), used to determine actual crop evapotranspiration, is often estimated from pan evaporation (EP) data. However, uncertainties in the relationship between ET _o and EP often result in unreliable estimate of crop evapotranspiration. This study investigated the relationship between measured and estimated crop evapotranspirations, ET _m and ET _e, respectively, at tillering (9–30 days after transplanting, DAT) and mid-growth (51–72 DAT) stages of a rice variety. ET _m was measured with a Marriott Tube-type Micro-lysimeter (hereafter referred to Micro-lysimeter) in a ponded rice field and ET _e was estimated from EP, which was measured by employing the US Weather Bureau Class ‘A’ Evaporation Pan (hereafter referred to Class A Evaporation Pan). A strong linear relation (r ² = 0.89) at the tillering stage and a weak relation (r ² = 0.48) at the mid-growth stage were obtained between ET _m and EP. The slope of this plot provided a pan-crop factor (K _p K _c), which was 0.81 at the tillering stage and 0.79 at the mid-growth stage. The ET _e versus ET _m relationship was also strongly linear (r ² = 0.90) at the tillering stage but weakly linear (r ² = 0.50) at the mid-growth stage. The pan-based method thus provided reliable estimates of evapotranspiration during the tillering stage of rice.     

The effect of water stress in regulated deficit irrigation on soybean yield (Glycine max [L.] Merr.)

The objective of this research was to investigate the effect of water stress in regulated deficit irrigation (RDI) on the yield of soybean growing on Ultisol soil. This research was conducted under plastic house on the experimental farm of Lampung Polytechnique from August to November 2004. The water stress treatments in regulated deficit irrigation were ET₁ (1.0 × ET_c), ET₂ (0.8 × ET_c), ET₃ (0.6 × ET_c), ET₄ (0.4 × ET_c) and ET₅ (0.2 × ET_c), arranged in a randomized block design with four replications. ET_c means crop evapotranspiration under standard condition, which was well watered. For example, the ET₂ (0.8 × ET_c) treatment means that the amount of supplied water per a day is the same as the crop adjustment evapotranspiration (ET_cadj) with the value 0.8 of water stress coefficient (K _s). The RDI treatments were carried out just at vegetative phase and its treatments were stopped at the beginning of flowering phase, and afterwards the treatments were watered at 1.0 × ET_c. The results showed that since week II, the soybean experienced stress throughout the growth period except ET₂ treatment. ET₂ treatment started to be stressed at week V and continued to be stressed until the harvest time. At the ET₃ treatment, the critical water content (θ_c) of soybean was reached at week II, and the θ_c was 0.24 m³/m³ on the average. The RDI at vegetative period significantly affected the yield. The highest yield was ET₁ (35.2 g/plant), followed by ET₂ (31.0 g/plant), ET₃ (18.1 g/plant), ET₄ (7.6 g/plant), and ET₅ (3.3 g/plant). The optimal water management of soybean with the highest yield efficiency was regulated deficit irrigation with water stress coefficient (K _s) of 0.80 for vegetative phase.     

Responses of potatoes (Solanum tuberosum L.) to irrigation and nitrogen in a hot,dry climate: I. Water use

The effects of differential irrigation and fertiliser treatments on the water use of potatoes (Solanum tuberosum L. cv. Desirée) were studied over 2 years in the hot dry climate of northeast Portugal. Total actual evapotranspiration (ET_c) ranged from 150 to 320 mm in 1988, and from 190 to 550 mm in 1989 depending mainly on irrigation treatment, potential evaporation rates (ET_p) and duration of the growing season. By comparison, the effects of nitrogen fertiliser on total water use were relatively small. Although nitrogen increased transpiration (larger leaf canopy), it reduced evaporation from the soil surface, in frequently irrigated plots, by similar amounts. As a result, in well-irrigated crops, the ET_c/ET_p ratio averaged 0.85 over the season, regardless of nitrogen level. Evaporation from the soil surface represented 15–25% of total water use by well-fertilised plants, but as much as 30–50% from the sparse stands of unfertilised crops. The proportion of water extracted from each depth increment of the silt-loam soil declined logarithmically, from the surface to 1.1 m depth, the maximum measured, for irrigated crops, and linearly when rain-fed. The ET_c/ET_p ratio fell below unity when 25–30% of the available water in the top metre had been depleted, equivalent to soil water deficits (SWDs) of 45–50 mm. By comparison, ET_c declined to zero when 75–90% of the available water had been extracted, corresponding to actual deficits of 135–150 mm. Peak ET_c rates reached 12–13 mm per day on days immediately following irrigation, nearly twice ET_p (possibly due to the influence of advection) but then declined logarithmically with time to about 3 mm per day within 5 days. Using the same data, a companion paper reports the influence of climatic conditions on the yield responses to water of potato crops grown in the region.     

Responses of rainwater conservation, precipitation-use efficiency and grain yield of summer maize to a furrow-planting and straw-mulching system in northern China

In the rain-fed areas of northern China, maize (Zea mays L.) is a main field crop, as it is well adapted to high temperatures and bright sunshine. However, low and variable rainfall and high evapotranspiration rates are common in water-limited environments during the growing season, and often mismatched rainfall events with the critical growth stages, making yield unstable. In this study, the performance of a furrow-planting and straw-mulching system was compared with the conventional flat-planting system in a double-crop culture of winter wheat (Triticum aestivum L.) and summer maize for two consecutive years (2005-2006 and 2006-2007). The four tested treatments were: conventional flat planting (F), furrow planting between ridges (B), flat planting with wheat straw-mulching (FS), and furrow planting between ridges with wheat-straw mulch (BS). Soil water content and leaf area index (LAI) were measured throughout the growing season each year, and grain yield and precipitation-use efficiency (PUE_Y) were determined.On average, ridge tillage combined with furrow planting increased maize yield by 430 kg ha⁻¹ (7.3%) and PUE_Y by 10.7% (1.5 kg ha⁻¹ mm⁻¹), compared with the conventional flat planting; furrow planting coupled with straw mulching increased yield by an additional 16.9% and PUE_Y by 19.4%, respectively. From jointing to maturity, LAI values of BS were significantly higher than those of F-system (55.6% vs. 26.1% in 2006 and 81.4% vs. 21.7% in 2007). Our data suggest that maize production adopted by furrow planting with straw-covered ridges performed best under seasonal average rainfall below 480 mm, which was associated with better synchronization of seasonal soil water supply and crop needs, leading to improved maize yield and PUE_Y.     

Variation in carbon isotope discrimination and other traits related to drought tolerance in upland cotton cultivars under dryland conditions

The search for traits related to drought resistance is a main step in the selection of cotton with improved performance under limited water supply. The effect of cultivar and drought conditions on the physiological traits, such as carbon isotope discrimination (Δ), photosynthesis (A), transpiration (E), stomatal conductance (g_s), leaf osmotic potential (ψ_o) and leaf-water content (LWC), were studied in Andalucia, Spain. The morphological traits, such as leaf area and specific leaf weight (SLW), were also evaluated. In the initial study performed with three cotton cultivars, positive associations between Δ and A, E and g_s were observed under increasing water stress. The A/g_s ratio was negatively associated with Δ, and a strong negative correlation was observed between SLW and Δ. In a further experiment, using a wider group of cultivars, an apparent genotypic variation in Δ was observed in plants after withholding irrigation. Genotypic variation was found for gas exchange (A, E, g_s) and leaf variables (LWC, SLW, ψ_o). No relationship was found between Δ and gas exchange or leaf-related traits. Considering both samplings as situations of different water availability, and plotting the data together, a low but positive correlation was observed between Δ and g_s or LWC, and negative between Δ and A/g_s. A remarkable correlation between LWC and gas exchange traits was found, whereas SLW was negatively correlated with A, A/E, and LWC. In dryland trials (1996 and 1997), the genotypic variation in LWC was positively associated with Δ. Under these conditions, an association between genotypic variation in Δ and A or A/E was observed. A positive correlation between yield and Δ was detected in 1996. Carbon isotope discrimination might be a useful tool for selecting drought-tolerant cotton genotypes but more studies are required to define more precisely the sampling conditions and the influence of factors affecting Δ and its relationship to crop yield.     

Growth,water use,and kernel abortion of maize subjected to drought at silking

Maize (Zea mays L.) grain yield is particularly sensitive to water deficits that coincide with the tasseling-silking period, causing marked reductions in grain number. More knowledge about crop responses to water supply is required, however, to explain the causes of kernel number reductions under the mild stresses characteristic of humid regions. The objectives of this study were to: (i) quantify crop evapotranspiration, E_c, and its relationship with shoot biomass production, grain yield, and kernel number; and (ii) determine the impact on final kernel number of supplying fresh pollen to silks whose appearance is delayed by water deficits at silking. Field experiments were conducted at Balcarce (37°45′S, 130 m) during 1988/89 and 1989/90 with two sowing dates (6 weeks apart) to provide differences in evaporative demand. Plastic covers were placed on the ground of water-deficit plots to generate a 40-day period of lowered water supply bracketing silking. Control plots received rain plus additional furrow irrigation in order to keep the ratio between crop (_c) and potential (E_p) Penman evapotranspiration greater than 0.9. Plant water status indicators revealed differences between treatments, but failed to reflect soil water status. Water deficit reduced plant height, maximum leaf area index, and shoot biomass. Shoot biomass accumulation was correlated with E_c, but higher water-use efficiencies (WUE) were found for the water-stress treatments. Grain yield was correlated to kernels m⁻² (r = 0.88; 6 d.f.), and both grain yield and kernels m⁻² were related to E_c during the treatment period, resulting in reductions of 4.7 grains m⁻² and 17.7 kg ha⁻¹ for each mm reduction in E_c. The number of kernels per ear did not improve when fresh pollen was applied to late appearing silks, suggesting that ovaries which failed to expose their silks synchronously with pollen shedding were deleteriously affected by water stress.     

基于称重式蒸渗仪的淮北平原冬小麦蒸散估算模型的本地化

为了解不同作物蒸散量估算方法在淮北地区的适用性,利用新马桥实验站称重式蒸渗仪测定了2016-2017年冬小麦全生育期的实际蒸散值,结合Hargreaves-Samani(H-S)、 FAO-56 PM、Turc、Makkind(Mak)、 Priestley-Taylor(P-T)、Mcloud(Mcl)和DeBruin-Keijman(D-K)7个模型,分析了冬小麦田的蒸散特征,将蒸散的估算值(ET_0)和实测值(ET_C)进行了对比。结果表明,相对于ET_C值,7个模型拟合得到的ET_0的RMSE值为0.99～2.29 mm·d~(-1),且H-S FAO-56 PMTurcMakP-TMclD-K; ET_C与ET_0的相关系数为0.74～0.97,其中FAO-56 PM的相关性最高,P-T、 Mak、 D-K、 H-S也表现出较好的相关性。综合来看,H-S法总体表现较好,更适合该地区。对6种主要气象要素与实测蒸散值进行主成分分析发现,温度是影响ET_C的主要因子,湿度、日照时数和平均风速(2 m)对淮北冬小麦田蒸散值的影响不大;H-S模型以温度数据为基础,利用线性订正法和湿度指数项订正法将H-S模型本地化后检验发现,其优化结果良好,RMSE降低(0.68 mm·d~(-1))。     

Evaluation and application of ORYZA2000 for irrigation scheduling of puddled transplanted rice in north west India

Water-saving technologies that increase water productivity of rice are urgently needed to help farmers to cope with irrigation water scarcity. This study tested the ability of the ORYZA2000 model to simulate the effects of water management on rice growth, yield, water productivity (WP), components of the water balance, and soil water dynamics in north-west India. The model performed well as indicated by good agreement between simulated and measured values of grain yield, biomass, LAI, water balance components and soil water tension, for irrigation thresholds ranging from continuous flooding (CF) to 70 kPa soil water tension.Using weather data for 40 different rice seasons (1970-2009) at Ludhiana in Punjab, India, the model predicted that there is always some yield penalty when moving from CF to alternate wetting and drying (AWD). With an irrigation threshold of 10 kPa, the average yield penalty was 0.8 t ha⁻¹ (9%) compared with CF, with 65% irrigation water saving, which increased to 79% at 70 kPa with a yield penalty of 25%. The irrigation water saving was primarily due to less drainage beyond the root zone with AWD compared to CF, with only a small reduction in evapotranspiration (ET) (mean 60 mm).There were tradeoffs between yield, irrigation amount and various measures of WP. While yield was maximum with CF, water productivity with respect to ET (WP_ET) was maximum (1.7 g kg⁻¹) for irrigation thresholds of 0 (CF) to 20 kPa, and irrigation water productivity (WP_I) increased to a maximum plateau (1.3 g kg⁻¹) at thresholds ≥30 kPa.Because of the possibility of plant stress at critical stages known to be sensitive to water deficit (panicle initiation (PI) and flowering (FL)), treatments with additional irrigations were superimposed for 2 weeks at one or both of these stages within the 10, 20 and 30 kPa AWD treatments. Ponding for two weeks at FL was more effective in reducing the yield penalty with AWD than ponding at PI, but the biggest improvement was with ponding at both stages. This reduced the average yield loss from 9% (0.8 t ha⁻¹) to 5% (0.5 t ha⁻¹) for AWD with thresholds of 10 and 20 kPa. However, maximum WP_I (1.1 g kg⁻¹) was achieved with an irrigation threshold of 20 kPa combined with more frequent irrigation at FL only, but with a greater yield penalty (8%). Thus the optimum irrigation schedule depends on whether the objective is to maximise yield, WP_ET or WP_I, which depends on whether land or water are most limiting. Furthermore, the optimum irrigation schedule to meet the short term needs of individual farmers may differ from that needed for sustainable water resource management.     

Estimation of paddy water productivity (WP) using hydrological model: an experimental study

Water productivity (WP) expresses the value or benefit derived from the use of water. A profound water productivity analysis was carried out at experimental field at Field laboratory, Centre for Water Resources, Anna University, India, for rice crop under different water regimes such as flooded (FL), alternative wet and dry (AWD) and saturated soil culture (SSC). The hydrological model soil-water-atmospheric-plant (SWAP), including detailed crop growth, i.e, WOFOST (World Food Studies) model was used to determine the required hydrological variables such as transpiration, evapotranspiration and percolation, and bio-physical variables such as dry matter and grain yield. The observed values of crop growth from the experiment were used for the calibration of crop growth model WOFOST. The water productivity values are determined using SWAP and SWAP–WOFOST. The four water productivity indicators using grain yield were determined, such as water productivity of transpiration (WP_T), evapotranspiration (WP_ET), percolation plus evapotranspiration (WP_ET+Q) and irrigation plus effective rainfall (WP_I+ER). The highest value of water productivity was observed from the flooded treatment and lowest value from the saturated soil culture in WP_T and WP_ET. This study, reveals that deep groundwater level and high temperature reduces the crop yield and water productivity significantly in the AWD and SSC treatment. This study reveals that in paddy fields 66% inflow water is recharging the groundwater. There is good agreement between SWAP and SWAP–WOFOST water productivity indicators.     

The response of autumn and spring sown sugar beet (Beta vulgaris L.) to irrigation in Southern Italy: Water and radiation use efficiency

The Apulia region in Southern Italy is an important area for sugar beet cultivation. It is characterised by clay soils and a hot-arid and winter-temperate climate. The capability of sugar beet to exploit solar radiation, water use and irrigation supply in root yield, total dry matter and sucrose production was studied and analysed in relation to two experimental factors: sowing date – autumn (October–December) and spring (March) – and irrigation regime – optimal and reduced (respectively with 100 and 60% of actual evapotranspiration). Data sets from three experiments of spring sowing and three of autumn sowing were used to calculate: (1) water use efficiency in the conversion in dry matter (WUE_dm, plant dry matter at harvest versus seasonal water use ratio), in sucrose (WUE_suc, sucrose yield versus seasonal water use ratio); (2) irrigation water use efficiency in the conversion in dry matter (IRRWUE_dm), in sucrose (IRRWUE_suc) and fresh root yield (IRRWUE_fr); and (3) radiation use efficiency (RUE, plant dry matter during the crop cycle and at harvest versus intercepted solar radiation ratio).Autumnal beet was more productive than spring for fresh root, plant total dry matter, sucrose yield and concentration; also WUE_suc and IRRWUE_s were higher in the autumnal sugar beet, but no difference was observed in WUE_dm (on average, 2.83 g of dry matter kg⁻¹ of water used). An average saving of about 26% of seasonal irrigation supply (equivalent to about 100 mm) was measured in the three years with the earliest sowing time. The optimal irrigation regime produced higher root yield, plant total dry matter and sucrose yield than the reduced one; on the contrary the IRRWUE_fr and IRRWUE_dm were higher in the reduced irrigation strategy. WUE_s and IRRUWE_s correlated positively with the length of crop cycle, expressed in growth degree days and, in particular, to the length of the period from full soil cover canopy to crop harvest, the period when plant photosynthetic activity and sucrose accumulation are at maximum rates. Seasonal RUE was higher in the spring than in the autumn sowing (1.14 μg J⁻¹ versus 1.00 μg J⁻¹). The RUE values during the crop cycle reached the maximum in the period around complete canopy soil cover. The results showed the importance for better use of water and radiation resources of autumnal sowing time and of reduced irrigation regime in sugar beet cropped in a Mediterranean environment.     

Short-term daily forecasting of crop evapotranspiration of rice using public weather forecasts

Accurate forecasts of daily crop evapotranspiration (ET_c) are essential for real-time irrigation management and water resource allocation. This paper presents a method for the short-term forecasting of ET_c using a single-crop coefficient approach and public weather forecasts. Temperature forecasts with a 7-day lead time in 2013–2015 were retrieved and entered into a calibrated Hargreaves–Samani model to compute daily reference evapotranspiration (ET₀) forecasts, while crop coefficient (K_c) empirical values were estimated from both observed ET_c value and calculated ET₀ values using the Penman–Monteith equation for the period of 2010–2012. Daily ET_c forecasts of irrigated double-cropping rice were determined for three growing seasons during the period of 2013–2015 and were compared with ET_c values measured by the weighing lysimeters at the Jiangxi experimental irrigation station in southeastern China. During the early rice season, the average mean absolute error (MAE) and root-mean-square-error (RMSE) values of ET_c forecasts ranged from 0.95 to 1.06 mm day^?1 and from 1.18 to 1.31 mm day^?1, respectively, and the average correlation coefficient (R) ranged from 0.39 to 0.54; for late rice, the average MAE and RMSE values ranged from 1.01 to 1.09 mm day^?1 and from 1.32 to 1.40 mm day^?1, respectively, and the average R value ranged from 0.54 to 0.58. There could be three factors responsible for errors in ET_c forecasts, including temperature forecast errors, K_c value errors and neglected meteorological variables in the HS model, including wind speed and relative humidity. In addition, ET_c was more sensitive to changes in temperature than K_c. The overall results indicated that it is appropriate to forecast ET_c with the proposed model for real-time irrigation management and water resource allocation.     

Comparison of selection indices to identify productive dry bean lines under diverse environmental conditions

This research was designed to quantify the effect of seasonal rainfall on production of dry bean (Phaseolus vulgaris L.) in the Rift Valley of East Africa, where insufficient soil moisture often limits productivity, and compare methods to identify productive lines. Twenty dry bean lines were evaluated for seed yield in a randomized complete-block design under soil moisture stress and nonstress environments during 1988, 1989 and 1992. Soil moisture stress levels were imposed by altering sowing dates (early vs. late) after the onset of the rainy season. Mean seed yield increased 8 kg ha⁻¹ for each mm of seasonal rainfall that occurred during the growing season. Lines differed in response to soil moisture stress, and their response varied with environments. Six selection indices, including arithmetic mean (AM), geometric mean (GM), drought response index (DRI), susceptibility index (S), response to drought (RD), and percent reduction (PR), were calculated for each line to determine correlations between indices and yields in stress (Y_s) and nonstress (Y_ns) environments. AM and GM were the only indices positively correlated with both Y_s and Y_ns. AM had the largest correlation with Y_ns (r=0.90) whereas GM had the largest correlation with Y_s (r=0.93). DRI, PR and S were correlated with Y_s (r=0.86, −0.82 and −0.83, respectively) but not with Y_ns. Conversely, the index RD was correlated with Y_ns (r=0.73) but not Y_s. The indices PR and S evaluated change in line performance across environments rather than line performance in either environment. GM and AM appear to be the most useful selection indices for identifying high yielding lines for both nonstress (early sown) and stress (late sown) conditions in the Rift Valley, while DRI has potential for use as a selection criteria only for stress environments.     

Nitrogen utilization efficiency of safflower hybrids and open-pollinated varieties under Mediterranean conditions

The identification of the factors determining nutrient utilization of safflower (Carthamus tinctorius L.) is useful for the successful introduction of the crop to the cropping system of a region. A field study was conducted to compare and analyze the relative importance of the various component traits causing variation in nitrogen utilization efficiency (NUE) of safflower under Mediterranean conditions. Ten genotypes, four hybrids and six open-pollinated varieties, were grown for two growing seasons without irrigation, on a silty clay (Typic Xerorthent) soil. Seed yield varied greatly among genotypes and ranged from 923 to 3391 kg ha⁻¹. Hybrids showed a mean seed yield superiority of 12.5% against varieties. Seed yield was the most important component of seed N yield and its contribution to the total variation in seed N yield among genotypes was at least 53%. NUE for biomass production during the seed-filling period was lower compared to that during the vegetative period. Genotypes differed in NUE for seed production (NUE_s) and the differences followed those of nitrogen harvest index (NHI). The contribution of NHI to the total variation in NUE_s among genotypes was much greater compared to that of yield per unit seed nitrogen and accounted for more than 79%. NUE_s is positively correlated with seed yield, suggesting that high yield was probably associated with more efficient exploitation of nitrogen. NUE_s is negatively correlated with (leaf + stem) N concentration at maturity, meaning that low straw N concentration may be indication of higher NUE_s. Results indicated that selection for NUE in safflower should be based on multiple criteria rather than just one criterion and also should be accompanied by evaluation for seed yield to ensure an improvement in both traits.     

Soybean yield and biomass responses to cumulative transpiration: Questioning widely held beliefs

Yield under drought for several crops has been established as a linear function of the cumulative water transpired during the growing season. For well-watered crops, however, there are no published data on how the duration of the cropping cycle and plant population affect the relationship between yield and transpiration. We evaluated the relationship between yield and estimated cumulative transpiration (T) or evapotranspiration (ET) for well-watered soybean (Glycine max [L.] Merr.) over a wide range of maturity groups (MG, 00–VI) and population densities (10–100 plants m⁻²) for 3 years. Daily T was estimated by determining the potential ET for a given day and multiplying this by the fraction of radiation intercepted by the crop, and a crop coefficient. Soil evaporation estimates were also made using an energy-balance approach after first subtracting the amount of radiation intercepted by the canopy. Daily values of T and ET were summed from emergence to R6. For all MG, cumulative T increased linearly with increasing population density (1.30 mm plant⁻¹ m⁻²), but predicted T at low populations (y intercept) more than quadrupled with increasing maturity, from 121 mm (MG 00) to 584 mm (MG VI). In contrast to the linear increase of yield to cumulative T for crops under drought stress, yield response to cumulative T for fully irrigated soybean differing in maturity was described well by an exponential model, predicting that 90% of the asymptotic yield would be obtained at 444 mm of T. Accounting for differences in harvest index and vapor-pressure deficit during the season among cultivars of differing maturity did not resolve the non-linear response of yield or biomass to cumulative T. These data indicate that for water-replete conditions, decreased T associated with short-season soybean need not result in decreased yield relative to full-season cultivars.     

Growth, yield and water productivity of zero till wheat as affected by rice straw mulch and irrigation schedule

Intensive cultivation of rice and wheat in north-west India has resulted in air pollution from rice straw burning, soil degradation and declining groundwater resources. The retention of rice residues as a surface mulch could be beneficial for moisture conservation and yield, and for hence water productivity, in addition to reducing air pollution and loss of soil organic matter. Two field experiments were conducted in Punjab, India, to study the effects of rice straw mulch and irrigation scheduling on wheat growth, yield, water use and water productivity during 2006-2008. Mulching increased soil water content and this led to significant improvement in crop growth and yield determining attributes where water was limiting, but this only resulted in significant grain yield increase in two instances. There was no effect of irrigation treatment in the first year because of well-distributed rains. In the second year, yield decreased with decrease and delay in the number of irrigations between crown root initiation and grain filling. With soil matric potential (SMP)-based irrigation scheduling, the irrigation amount was reduced by 75 mm each year with mulch in comparison with no mulch, while maintaining grain yield. Total crop water use (ET) was not significantly affected by mulch in either year, but was significantly affected by irrigation treatment in the second year. Mulch had a positive or neutral effect on grain water productivity with respect to ET (WP_ET) and irrigation (WP_I). Maximum WP_I occurred in the treatment which received the least irrigation, but this was also the lowest yielding treatment. The current irrigation scheduling guidelines based on cumulative pan evaporation (CPE) resulted in sub-optimal irrigation (loss of yield) in one of the two years, and higher irrigation input and lower WP_I of the mulched treatment in comparison with SMP-based irrigation scheduling. The results from this and other studies suggest that farmers in Punjab greatly over-irrigate wheat. Further field and modelling studies are needed to extrapolate the findings to a wider range of seasonal and site conditions, and to develop simple tools and guidelines to assist farmers to better schedule irrigation to wheat.     

Yield response of corn to irrigation and nitrogen fertilization in a Mediterranean environment

Productivity and resource-use efficiency in corn (Zea mays L.) are crucial issues in sustainable agriculture, especially in high-demand resource crops such as corn. The aims of this research were to compare irrigation scheduling and nitrogen fertilization rates in corn, evaluating yield, water (WUE), irrigation water (IRRWUE) and nitrogen use (NUE) efficiencies. A 2-year field experiment was carried out in a Mediterranean coastal area of Central Italy (175 mm of rainfall in the corn-growing period) and corn was subjected to three irrigation levels (rainfed and supply at 50 and 100% of crop evapotranspiration, ETc) in interaction with three nitrogen fertilization levels (not fertilized, 15 and 30 g (N) m⁻²). The results indicated a large yearly variability, mainly due to a rainfall event at the silking stage in the first year; a significant irrigation effect was observed for all the variables under study, except for plant population. Nitrogen rates affected grain yield plant⁻¹ and ear⁻¹, grain and biomass yield, HI, WUE, IRRWUE and NUE, with significant differences between non-fertilized and the two fertilized treatments (15 and 30 g (N) m⁻²). Furthermore, deficit irrigation (50% of ETc) was to a large degree equal to 100% of the ETc irrigation regime. A significant interaction “N × I” was observed for grain yield and WUE. The effect of nitrogen availability was amplified at the maximum irrigation water regime. The relationships between grain yield and evapotranspiration showed basal ET, the amount necessary to start producing grain, of about 63 mm in the first and 206 mm in the second year. Rainfed crop depleted most of the water in the 0–0.6 m soil depth range, while irrigated scenarios absorbed soil water within the profile to a depth of 1.0 m. Corn in a Mediterranean area can be cultivated with acceptable yields while saving irrigation water and reducing nitrogen supply and also exploiting the positive interaction between these two factors, so maximizing resource-use efficiency.     

Observations on effect of seeding pattern on water-use efficiency of durum wheat in semi-arid areas of Morocco

In semi-arid areas of Morocco, soil evaporation is rapid during early growth period of durum wheat (Triticum turgidum cv. group durum). Experiments were conducted in the field during 1995–1996 and 1996–1997 to see if early shading of soil through the use of narrow row spacing and adequate plant population would help conserve water and hence increase wheat grain yield and water-use efficiency. Three seeding rates, 200, 300 and 400 kernels m⁻² and two distances between rows, 24 cm (check) and 12 cm were tested in a split-plot design. Results revealed that grain yield, total above-ground dry matter production and water-use efficiency were increased when row spacing was reduced. The effect of seeding rate was significant only in 1995–1996 where the highest plant population gave the lowest yield. Actual evapotranspiration measured for the whole growing season was not affected by any treatment. It appears that in semi-arid areas of Morocco, grain yield and water-use efficiency are more related to water use pattern during the growing season than to total evapotranspiration.     

Transpiration efficiencies of maize and beans in semi-arid Kenya

Maize and bean were grown under varying levels of nitrogen fertilizer, plant population, and irrigation at Kiboko, Kenya in the short rains 1990, 1991, 1992 and the long rains 1991. The production of dry matter was not affected significantly by any treatment, because treatments only had a small impact on the balance between evaporation and transpiration. In all seasons the greatest loss of water from the profile was through direct evaporation from the soil surface. Transpiration was always less than 25% of rainfall. The ratio of transpiration (T) to evapotranspiration (E + T) was small (0.23), but increased from 0.15 to 0.40 as rainfall increased from 158 mm in the long rains 1991 to 470 mm in the short rains 1992. Treatments had little impact on the balance between transpiration and evaporation from the soil surface. The average transpiration efficiencies for maize and bean were 89 and 29 kg shoot dry matter ha⁻¹ mm⁻¹, respectively. For each crop there was a 60% change in transpiration efficiency between the short and the long rain season which could be accounted for by differences in saturation vapour pressure deficit.