Effect of soil matric potential,method of irrigation and nitrogen fertilization on yield,quality, nutrient uptake and water use of radish (Raphanus sativus L.)

Summary Field experiments carried out at the Indian Institute of Horticultural Research, Bangalore during 1983 and 1984 on radish indicated that frequent irrigations when soil matric potential reached –20 kPa at 18 cm depth resulted in maximum root yield, lower NO₃-N content in roots, higher N, P, K, Ca and WUE of radish.Contribution No. 63/86 from Indian Institute of Horticultural Research, Bangalore, India     

Plant water relations and nutrient uptake in French bean

Summary Field investigations carried out at the Indian Institute of Horticultural Research, Bangalore, during 1985–1986 and 1986–1987 with French bean crops indicated that irrigation when soil matric potential at 0.15 m depth reached — 45 kPa resulted in highest dry matter production, green pod yield, nutrient uptake and water use efficiency (WUE) as compared to irrigations scheduled at -65 or -85 kPa. The difference in pod yield between irrigations scheduled at -25 and -45 kPa was not significant. Increasing soil moisture stress increased the canopy temperature and adversely affected plant water relations. There was a quadratric relationship between green pod yield and evapotranspiration (ET) with the yield-maximising ET ranging between 268 and 299 mm. Nitrogen fertilization significantly increased green pod yield, nutrient uptake and WUE but had no marked effect on water relations and canopy temperature.Contribution No. 234/88 of Indian Institute of Horticultural Research, Bangalore, India     

Effects of untreated and treated wastewater irrigation on some chemical properties of cauliflower (Brassica olerecea L. var. botrytis) and red cabbage (Brassica olerecea L. var. rubra) grown on calcareous soil in Turkey

The use of wastewater for irrigation is increasingly being considered as a technical solution to minimize soil degradation and to restore nutrient content of soils. The aims of this study were to test if wastewater irrigation could improve soil fertility without affecting the quality of soils and plants. A field experiment was conducted in 2006 to investigate the effects of irrigation with untreated, and preliminary and primary treated wastewater on macro- and micronutrient distribution within the soil profile, yield and mineral content of cauliflower and red cabbage plants grown on a calcareous Aridisol in eastern Anatolia, Erzurum province, Turkey. Wastewater irrigation affected significantly soil chemical properties in the 0–30 cm soil layer and plant nutrient content after harvest. Application of wastewater increased soil salinity, organic matter, exchangeable Na, K, Ca, Mg, plant available phosphorus and microelements, and decreased soil pH. Wastewater irrigation treatments also increased the yield as well as N, P, K, Ca, Mg, Na, Fe, Mn, Zn, Cu, Pb, Ni and Cd contents of cauliflower and red cabbage plants. The highest yield, macro- and micronutrient uptake of cauliflower and red cabbage plants were obtained with the untreated wastewater. Undesirable side effects such as heavy metal contamination in soil and plant, and salinity were not observed with the application of wastewater. It can be concluded that untreated wastewater can be used confidently, in the short term, in agricultural land, while primary treated wastewater can be used in sustainable agriculture in the long term.     

Tomato nitrogen accumulation and fertilizer use efficiency on a sandy soil, as affected by nitrogen rate and irrigation scheduling

Tomato production systems in Florida are typically intensively managed with high inputs of fertilizer and irrigation and on sandy soils with low inherent water and nutrient retention capacities; potential nutrient leaching losses undermine the sustainability of such systems. The objectives of this 3-year field study were to evaluate the interaction between N-fertilizer rates and irrigation scheduling on crop N and P accumulation, N-fertilizer use efficiency (NUE) and NO₃-N leaching of tomato cultivated in a plastic mulched/drip irrigated production system in sandy soils. Experimental treatments were a factorial combination of three irrigation scheduling regimes and three N-rates (176, 220, and 330 kg ha⁻¹). Irrigation treatments included were: (1) surface drip irrigation (SUR) both the irrigation and fertigation line placed underneath the plastic mulch; (2) subsurface drip irrigation (SDI) where the irrigation drip was placed 0.15 m below the fertigation line which was located on top of the bed; and (3) TIME (conventional control) with the irrigation and fertigation lines placed as in SUR and irrigation applied once a day. Except for the TIME treatment all irrigation treatments were soil moisture sensor (SMS)-based with irrigation occurring at 10% volumetric water content. Five irrigation windows were scheduled daily and events were bypassed if the soil water content exceeded the established threshold. The use of SMS-based irrigation systems significantly reduced irrigation water use, volume percolated, and nitrate leaching. Based on soil electrical conductivity (EC) readings, there was no interaction between irrigation and N-rate treatments on the movement of fertilizer solutes. Total plant N accumulation for SUR and SDI was 12-37% higher than TIME. Plant P accumulation was not affected by either irrigation or N-rate treatments. The nitrogen use efficiency for SUR and SDI was on the order of 37-45%, 56-61%, and 61-68% for 2005, 2006 and 2007, respectively and significantly higher than for the conventional control system (TIME). Moreover, at the intermediate N-rate SUR and SDI systems reduced NO₃-N leaching to 5 and 35 kg ha⁻¹, while at the highest N-rate corresponding values were 7 and 56 kg N ha⁻¹. Use of N application rates above 220 kg ha⁻¹ did not result in fruit and/or shoot biomass nor N accumulation benefits, but substantially increased NO₃-N leaching for the control treatment, as detected by EC monitoring and by the lysimeters. It is concluded that appropriate use of SDI and/or sensor-based irrigation systems can sustain high yields while reducing irrigation application as well as reducing NO₃-N leaching in low water holding capacity soils.     

合理灌溉施肥对贺兰山东麓初果期酿酒葡萄的影响研究

贺兰山东麓葡萄管理中存在大水漫灌水分利用率低以及重视氮磷钾肥,忽视中量元素和腐殖酸类肥料等问题。针对初果期酿酒葡萄需水需肥规律采用田间试验的方式分别设置合理的施肥及灌溉试验后,分别测定其生长发育以及品质和产量。结果显示:在滴灌节水50%的基础上,滴灌促进了酿酒葡萄新梢的生长,增加了叶片磷素、叶柄氮素和钾素含量积累,显著增加了果实可溶性固形物及Vc,降低了总酸度;钙镁硫肥显著提升了叶片全氮和可溶性糖含量,总酸度降低;腐殖酸肥能显著增加叶片干重,并显著提升可溶性糖和Vc含量。在滴灌条件下增施中量营养元素和腐殖酸肥对贺兰山东麓酿酒葡萄生长和产量品质有巨大促进作用。     

Nitrogen fertilizer management of cotton grown under drip irrigation in a grumusol

Summary A field experiment was carried out for two years on a grumusol (Typic chromoxerert) soil at Merhavya, Israel, to study the influence of different concentrations of N in soil solution on the growth and yield of drip-irrigated cotton (Gossypium hirsutum L.) var. Acala SJ-2. The N-concentrations in the soil solution used were: 0, 12.5, 25, 50, 75 and 100 ppm N. The soil was analyzed for moisture and NO₃-N every two weeks and the concentration of NO₃-N in the soil solution was calculated. When the NO₃-N concentration was less than the above-mentioned levels, N-fertilizer was added in the irrigation water to match these concentrations. If the tested soils showed higher concentrations, no N fertilizer was applied.The maximum yields of seed cotton obtained were 6.3 ton h^–1 in the first year, and 5.7 ton ha^–1 in the second year. Concentrations below 25 ppm N in the soil solution reduced the cotton seed and lint yields, but concentrations of 50 ppm N and above did not increase the yields and sometimes even decreased them. Application of more nitrogen caused excessive vegetative growth and less seed-cotton and lint.The results show that soil nitrate analysis during the cotton season can be used to monitor the N supplied by drip irrigation.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 1418-E, 1985 series     

土壤水分含量对加工番茄产量和品质影响的研究

试验从加工番茄开花期开始，设4个水分处理（分别以0～60cm土层灌前土壤田间持水量的40％～45％、55％～60％、70％～75％和85％～90％作为各处理的灌溉下限含水量临界值，灌溉上限为田间持水量的90％），分析不同水分状况下加工番茄的产量和果实品质。试验结果表明，加工番茄的产量、品质与土壤含水量密切相关，灌前过高或过低的土壤含水量会影响产量及茄红素、可溶性固形物、可溶性糖、可溶性酸等品质指标，灌前土壤相对田间持水量为70％～75％处理的加工番茄产量最高，品质较好，水分利用效率最高，既能实现高产高效，又可达到节水灌溉的目的。     

Spatial and temporal distributions of nitrogen and crop yield as affected by nonuniformity of sprinkler fertigation

Deep percolation and nitrate leaching are important considerations in the design of sprinkler systems. Field experiments were therefore conducted to investigate the influence of nonuniformity of sprinkler irrigation on deep percolation and spatial distributions of nitrogen and crop yield during the growing season of winter wheat at an experiment station in Beijing, China. Three experimental plots of a sandy clay loam soil in the 0–40 cm depth interval and a loamy clay soil below 40 cm were irrigated with a sprinkler irrigation system that had a seasonal averaged Christiansen irrigation uniformity coefficient (CU) varying from 72 to 84%. Except for the fertilizer applied before planting, fertilizer was applied with the sprinkler irrigation system. The corresponding seasonal averaged CU for fertigation varied from 71 to 85%. Daily observation of matrix water potentials in the root zone showed that little deep percolation occurred. Consequently, the effect of sprinkler uniformity on deep percolation was minor during the irrigation season for the soil tested. Intensive gravimetric soil core samplings were conducted several times during the irrigation season in a grid of 5 m × 5 m for each plot to determine the spatial and temporal variation of NH₄-N and NO₃-N contents. Soil NH₄-N and NO₃-N exhibited high spatial variability in depth and time during the irrigation season with CU values ranging from 23 to 97% and the coefficient of variation ranging from 0.04 to 1.06. A higher uniformity of sprinkler fertigation produced a more uniform distribution of NH₄-N, but the distribution of NO₃-N was not related to fertigation. Rather it was related to the spatial variability of NO₃-N before fertigation began. At harvest, the distribution of dry matter above ground, nitrogen uptake, and yield were measured and the results indicated that sprinkler fertigation uniformity had insignificant effects on the parameters mentioned above. Field experimental results obtained from this study suggest that sprinkler irrigation if properly managed can be used as an efficient and environment-friendly method of applying water and fertilizers.     

Water and nitrate movement in drip-irrigated onion under fertigation and irrigation treatments

Frequent fertigation of crops is often advocated in the technical and popular literature, but there is limited evidence of the benefits of high-frequency fertigation. Field experiments were conducted on an Indo-American Hybrid var., Creole Red, of onion crop during three winter seasons of 1999–2000 through 2001–2002 in coarse-textured soil of Delhi under the semi-arid region of India. Three irrigation levels of 60, 80 and 100% of the crop evapotranspiration (ET) and four fertigation frequencies of daily, alternate day, weekly and monthly comprised the fertigation treatment. Analysis of soil samples indicated considerable influence of fertigation frequency on NO₃-N distribution in soil profile. NO₃-N in lower soil profiles (30.0–60.0 cm soil depth) was marginally affected in daily, alternate day and weekly fertigation. However, fluctuations of NO₃-N content in 0.0–15.0, 15.0–30.0, 30.0–45.0 and 45.0–60.0 cm soil depth was more in monthly fertigation frequency. The level of soil NO₃-N after the crop season shows that more NO₃-N leached through the soil profile in monthly fertigation frequency. Amounts of irrigation water applied in three irrigation treatments proved to be too small to cause significant differences in the content of NO₃-N leached beyond rooting depth of onion. Yield of onion was not significantly affected in daily, alternate day and weekly fertigation, though there was a trend of lower yields with monthly fertigation. The highest yield was recorded in daily fertigation (28.74 t ha⁻¹) followed by alternate day fertigation (28.4 t ha⁻¹). Lowest yield was recorded in monthly fertigation frequency (21.4 t ha⁻¹). Application of 56.4 cm irrigation water and 3.4 kg ha⁻¹ urea per fertigation (daily) resulted in highest yield of onion with less leaching of NO₃-N.     

膜下滴灌水肥耦合对葡萄生长发育、产量和品质的影响

以‘寒香蜜’葡萄为试材,开展田间膜下滴灌施肥试验,探讨膜下滴灌水肥耦合对葡萄生长发育、产量及其品质的影响。其中,灌水量设置4个水平,分别为180(W1)、270(W2)、360(W3)、450 mm(W4);施肥量设置4个水平,分别为N 150 kg/hm~2+P_2O_5120 kg/hm~2+K_2O 165 kg/hm~2(F1)、N 225 kg/hm~2+P_2O_5180 kg/hm~2+K_2O248 kg/hm~2(F2)、N 300 kg/hm~2+P_2O_5240 kg/hm~2+K_2O 330 kg/hm~2(F3)、N 450 kg/hm~2+P_2O_5360 kg/hm~2+K_2O495 kg/hm~2(F4),共计16个处理。试验结果表明,在灌水量为W2(270 mm)及施肥量为F2(N 225 kg/hm~2+P_2O_5180 kg/hm~2+K_2O 248 kg/hm~2)的组合处理下,葡萄新梢生长效果较好,叶片叶绿素含量在整个生育期均处于较高水平,于新梢生长期、开花期、果实膨大期和果实着色期分别达到3.28、3.77、3.65、3.53 mg/g;F3W4处理果形指数最高,但除F1W1和F1W2处理外,其他各处理间差异均不显著。此外,果实产量和品质指标表明,虽然F2W2处理对应的葡萄果实产量并不是最高,但其与产量最高的F2W3处理间差异并不显著,且F2W2处理果实品质较理想,其果实可溶性固形物含量最高,达到19.64%,果实可溶性糖质量分数和果实硬度也较优,分别为17.00%和0.71 kg/cm~2。综合分析结果表明,F2W2水肥组合对稳定葡萄产量和改善果实品质有积极的意义。     

极端干旱区滴灌葡萄水肥适宜用量主成分分析法

为了探明极端干旱区滴灌葡萄水肥适宜用量,利用主成分分析法,以试验区内成龄无核白葡萄为研究对象,综合评价得出高产高效的最优水肥处理.设置灌水、施肥2个因素,其中设灌水处理4个水平:6 000(W1),6 750(W2),7 500(W3),8 250 m³/hm²(W4);施肥处理3水平:450(F1),750(F2),1 050 kg/hm²(F3).结果表明:滴灌葡萄产量、水肥利用效率及品质受水肥交互作用影响均具有统计学意义(P<0.01);可滴定酸受灌水量与施肥量的影响均具有统计学意义(P<0.05);滴灌葡萄产量、灌溉水利用效率、肥料偏生产力、可溶性固形物及维生素C分别受灌水量和施肥量影响均具有统计学意义(P<0.01),产量最大处理W3F2相对于最小处理增产29.76%,可溶性固形物以处理W3F2的含量最大,可滴定酸在处理W4F2下取得最大值,且处理W3F2与最大处理间差异不具有统计学意义(P>0.05),不同水肥处理的维生素C每100 g溶液质量为7.37~8.52 mg,且处理W3F2与最大处理W4F3间差异不具有统计学意义(P>0.05),品质指标在处理W3F2下取得较优.主成分分析法结果表明,极端干旱区滴灌葡萄最佳水肥处理为W3F2,其中N,P₂O₅,K₂O分别为300,150和300 kg/hm².     

Nitrate leaching in a silage maize field under different irrigation and nitrogen fertilizer rates

Quantification of the interactive effects of nitrogen (N) and water on nitrate (NO₃) loss provides an important insight for more effective N and water management. The goal of this study was to evaluate the effect of different irrigation and nitrogen fertilizer levels on nitrate-nitrogen (NO₃-N) leaching in a silage maize field. The experiment included four irrigation levels (0.7, 0.85, 1.0, and 1.13 of soil moisture depletion, SMD) and three N fertilization levels (0, 142, and 189 kg N ha⁻¹), with three replications. Ceramic suction cups were used to extract soil solution at 30 and 60 cm soil depths for all 36 experimental plots. Soil NO₃-N content of 0-30 and 30-60-cm layers were evaluated at planting and harvest maturity. Total N uptake (NU) by the crop was also determined. Maximum NO₃-N leaching out of the 60-cm soil layer was 8.43 kg N ha⁻¹, for the 142 kg N ha⁻¹ and over irrigation (1.13 SMD) treatment. The minimum and maximum seasonal average NO₃ concentration at the 60 cm depth was 46 and 138 mg l⁻¹, respectively. Based on our findings, it is possible to control NO₃ leaching out of the root zone during the growing season with a proper combination of irrigation and fertilizer management.     

Timing of limited irrigation and N-injection for grain sorghum

When subsurface irrigation sources are lacking in humid and subhumid regions, high yearly precipitation may allow for storage of surface water in farm ponds and lakes for irrigation. Irrigation at selected growth stages may avoid critical stress for crops with some drought tolerance, such as grain sorghum [Sorghum bicolor (L.) Moench]. Because grain sorghum is responsive to N, injecting fertilizer N through the irrigation system also may improve production. The objective of this study was to determine the effect of timing of limited-amount irrigation and N fertigation on grain sorghum yield; yield components; grain N content; and N uptake at the 9-leaf, boot, and soft dough stages. The experiment was conducted from 1984 to 1986 on a Parsons silt loam (fine, mixed, thermic, Mollic Albaqualf). The experiment was designed as a 6 × 2 factorial plus two reference treatments. Six timings for irrigation were targeted at the 9-leaf (9L), boot (B), soft dough (SD), 9L-B, 9L-SD, and B-SD growth stages. N application systems were either 112 kg N ha^–1 surface-banded preplant or 56 kg N ha^-1 preplant and 56 kg N ha^–1 injected through the irrigation at a rate of 28 kg N ha^–1 per 2.5 cm of irrigation. Two reference treatments included were one receiving N but no irrigation and one receiving neither N nor irrigation. In 1984, irrigation generally increased grain sorghum yield by nearly 1 Mg ha^–1. However, yield was not affected by selection of irrigation timing, N application method, or the interaction of the two factors. This was partly because early irrigations increased kernels/head, whereas later irrigations increased kernel weight. Above average rainfall during the growing season, especially just prior to the 9-leaf, boot, and soft dough growth stages, resulted in no irrigations in 1985. In 1986, yield was increased by early (9-leaf) irrigations as compared to soft dough irrigations. Early irrigations resulted in higher kernels/head; however, rainfall after the soft dough irrigation may have masked any treatment effect on kernel weight. As in 1984, N application method did not affect grain sorghum yields, even though yield was reduced to less than 3 Mg ha^–1 with no N nor irrigation. In both 1984 and 1986, N uptake at succeeding growth stages appeared to respond to irrigations made at previous growth stages. Injecting half of the fertilizer N through the irrigation system did not affect N uptake compared to applying all N preplant. The lack of response to fertigation may be related to the low leaching potential of the soil used in this study.Contribution No. 92-606-J, Kansas Agricultural Experiment Station     

Nitrogen fixation in a white clover-grass pasture irrigated with saline groundwater

Nitrogen (N₂) fixation in an irrigated white clover-grass sward was estimated using the ¹⁵N isotope dilution technique following the addition of K¹⁵NO₃ at 0.5 gN m^–2 and 80 atom % ¹⁵N in a field study during the 1990–91 season. Two water salinity treatments (channel water; EC_w = 0.07 and groundwater; 2.4 dS m^–1) and four irrigation frequencies were included in a factorial design with four replicates. The channel water treatments were irrigated when pan evaporation minus rainfall equalled 50 mm, whereas the groundwater treatments were irrigated at deficits of 40, 50, 65 or 80 mm. Cumulative dry matter of the clover was significantly less in treatments irrigated with saline groundwater compared to channel water at day 164, and soil salinities (EC_e) increased on average from 2.3 to 5.07 dS m^–1. In contrast, salinity of the irrigation water had no effect on the cumulative yield of grass. Cumulative dry matter of the grass and clover were not affected by groundwater irrigation frequency. Total N accumulation by the grass did not differ significantly between treatments. However, total N accumulation in white clover was significantly less (P < 0.05) in all treatments irrigated with groundwater compared to channel water. Neither the N concentrations of the grass nor the clover differed significantly between the salinity treatments. Salinity and irrigation frequency had no effect on the proportion of clover N (P_atm) derived from N₂ fixation. The values of P_atm were high throughout, and increased progressively from 0.78 at day 39 to 0.91 at day 164 (P < 0.01). However, the yield of fixed N was lower in clover when watered with groundwater compared to channel water (P < 0.01). Thus low to moderate soil salinity did not affect the symbiotic dependence of clover, but the yield of biologically-fixed N was depressed through a reduction in the dry matter yield of the legume.     

滴灌肥不同施用量对设施灵武长枣生长、产量和品质的影响

与传统施肥方式相比较,滴灌肥具有提高肥料利用率、施肥肥效快等诸多优势,以5a生灵武长枣为研究对象,分别设置405、540、675、810kg/hm~2滴灌肥施用量处理以及复合肥施用量900kg/hm~2的常规施肥处理,研究不同滴灌肥处理对长枣生长及产量和品质的影响,试验结果表明675kg/hm~2处理下,长枣新梢生长量、枣吊数、果实维生素C、可溶性固形物均显著高于其余各处理,产量比常规施肥提高了17.3%;在滴灌肥施用量为405kg/hm~2处理下,果实中总酸含量最低,果实硬度最高;在施肥量675kg/hm~2处理下,长枣生长状况良好,产量最高,品质较好。     

Evaluating irrigation applied and nitrogen leached using different smart irrigation technologies on bahiagrass (Paspalum notatum)

Irrigation technologies [i.e., automatic timer, automatic timer with rain sensor, automatic timer with soil water sensor (SWS), and evapotranspiration (ET) controller] were compared in a bahiagrass plot study by measuring irrigation applied, water volumes drained, and NO₃–N and NH₄–N leached. All irrigation technologies were scheduled to irrigate on Sunday and Thursday. Three different irrigation depths were evaluated with the automatic timer: 15, 19, and 32 mm. SWS treatment allowed scheduled irrigation if soil water content was estimated to be below 70 % of water holding capacity, while the ET treatment allowed scheduled irrigation if soil water content was estimated to be below 50 % of plant available water. The rain sensor, SWS, and ET controller treatments applied significantly less water (p < 0.05) than the automatic timer treatment (which irrigates on specific days and times without regard to system conditions), reducing water by 17–49, 64–75, and 66–70 %, respectively. NO₃–N and NH₄–N were only significantly different after the second fertilizer application, which coincided with the 32 mm per event irrigation rate for the automatic timer treatment. Under these conditions, the automatic timer treatment had significantly greater NO₃–N and NH₄–N leachate than other treatments due to greater occurrence of soil water content exceeding water holding capacity, which resulted in drainage. Findings suggest that water can be saved using rain sensors, SWSs, or ET controllers and that leachate NO₃–N and NH₄–N can be reduced using rain sensors, SWSs, or ET controllers.     

Simulation of transpiration, drainage, N uptake, nitrate leaching, and N uptake concentration in tomato grown in open substrate

Free-drainage or “open” substrate system used for vegetable production in greenhouses is associated with appreciable NO₃⁻ leaching losses and drainage volumes. Simulation models of crop N uptake, N leaching, water use and drainage of crops in these systems will be useful for crop and water resource management, and environmental assessment. This work (i) modified the TOMGRO model to simulate N uptake for tomato grown in greenhouses in SE Spain, (ii) modified the PrHo model to simulate transpiration of tomato grown in substrate and (iii) developed an aggregated model combining TOMGRO and PrHo to calculate N uptake concentrations and drainage NO₃⁻ concentration. The component models simulate NO₃⁻-N leached by subtracting simulated N uptake from measured applied N, and drainage by subtracting simulated transpiration from measured irrigation. Three tomato crops grown sequentially in free-draining rock wool in a plastic greenhouse were used for calibration and validation. Measured daily transpiration was determined by the water balance method from daily measurements of irrigation and drainage. Measured N uptake was determined by N balance, using data of volumes and of concentrations of NO₃⁻ and NH₄⁺ in applied nutrient solution and drainage. Accuracy of the two modified component models and aggregated model was assessed by comparing simulated to measured values using linear regression analysis, comparison of slope and intercept values of regression equations, and root mean squared error (RMSE) values. For the three crops, the modified TOMGRO provided accurate simulations of cumulative crop N uptake, (RMSE = 6.4, 1.9 and 2.6% of total N uptake) and NO₃⁻-N leached (RMSE = 11.0, 10.3, and 6.1% of total NO₃⁻-N leached). The modified PrHo provided accurate simulation of cumulative transpiration (RMSE = 4.3, 1.7 and 2.4% of total transpiration) and cumulative drainage (RMSE = 13.8, 6.9, 7.4% of total drainage). For the four cumulative parameters, slopes and intercepts of the linear regressions were mostly not statistically significant (P < 0.05) from one and zero, respectively, and coefficient of determination (r²) values were 0.96-0.98. Simulated values of total drainage volumes for the three crops were +21, +1 and −13% of measured total drainage volumes. The aggregated TOMGRO-PrHo model generally provided accurate simulation of crop N uptake concentration after 30-40 days of transplanting, with an average RMSE of approximately 2 mmol L⁻¹. Simulated values of average NO₃⁻ concentration in drainage, obtained with the aggregated model, were −7, +18 and +31% of measured values.     

Trickle and sprinkler irrigation of potato (Solanum tuberosum L.) in the Middle Anatolian Region in Turkey

The potato (Solanum tuberosum L.) is widely planted in the Middle Anatolian Region, especially in the Nigde-Nevsehir district where 25% of the total potato growing area is located and produces 44% of the total yield. In recent years, the farmers in the Nigde-Nevsehir district have been applying high amounts of nitrogen (N) fertilizers (sometimes more than 900 kg N ha⁻¹) and frequent irrigation at high rates in order to get a much higher yield. This situation results in increased irrigation and fertilization costs as well as polluted ground water resources and soil. Thus, it is critical to know the water and nitrogen requirements of the crop, as well as how to improve irrigation efficiency. Field experiments were conducted in the Nigde-Nevsehir (arid) region on a Fluvents (Entisols) soil to determine water and nitrogen requirements of potato crops under sprinkler and trickle irrigation methods. Irrigation treatments were based on Class A pan evaporation and nitrogen levels were formed with different nitrogen concentrations.The highest yield, averaging 47,505 kg ha⁻¹, was measured in sprinkler-irrigated plots at the 60 g m⁻³ nitrogen concentration level in the irrigation treatment with limited irrigation (480 mm). Statistically higher tuber yields were obtained at the 45 and 60 g m⁻³ nitrogen concentration levels in irrigation treatments with full and limited irrigation. Maximum yields were obtained with about 17% less water in the sprinkler method as compared to the trickle method (not statistically significant). On the loam and sandy loam soils, tuber yields were reduced by deficit irrigation corresponding to 70% and 74% of evapotranspiration in sprinkler and trickle irrigations, respectively. Water use of the potato crop ranged from 490 to 760 mm for sprinkler-irrigated plots and 565–830 mm for trickle-irrigated treatments. The highest water use efficiency (WUE) levels of 7.37 and 4.79 kg m⁻³ were obtained in sprinkle and trickle irrigated plots, respectively. There were inverse effects of irrigation and nitrogen levels on the WUE of the potato crops. Significant linear relationships were found between tuber yield and water use for both irrigation methods. Yield response factors were calculated at 1.05 for sprinkler methods and 0.68 for trickle methods. There were statistically significant linear and polynomial relationships between tuber yield and nitrogen amounts used in trickle and sprinkler-irrigated treatments, respectively. In sprinkler-irrigated treatments, the maximum tuber yield was obtained with 199 kg N ha⁻¹. The tuber cumulative nitrogen use efficiency (NUE_cu) and incremental nitrogen use efficiency (NUE_in) were affected quite differently by water, nitrogen levels and years. NUE_cu varied from 16 to 472 g kg⁻¹ and NUE_in varied from 75 to 1035 g kg⁻¹ depending on the irrigation method. In both years, the NH₄-N concentrations were lower than NO₃-N, and thus the removed nitrogen and nitrogen losses were found to be 19–87 kg ha⁻¹ for sprinkler methods and 25–89 kg ha⁻¹ for trickle methods. Nitrogen losses in sprinkler methods reached 76%, which were higher than losses in trickle methods.     

Yield and quality of melon grown under different irrigation and nitrogen rates

During 2 years, a melon crop (Cucumis melo L. cv. Sancho) was grown under field conditions to investigate the effects of different nitrogen (N) and irrigation (I) levels on fruit yield, fruit quality, irrigation water use efficiency (IWUE) and nitrogen applied efficiency (NAE). The statistical design was a split-plot with four replications, where irrigation was the main factor of variation and N was the secondary factor. In 2005, irrigation treatments consisted of applying daily a moderate water stress equivalent to 75% of ETc (crop evapotranspiration), a 100% ETc control and an excess irrigation of 125% ETc (designated as I₇₅, I₁₀₀ and I₁₂₅), while the N treatments were 30, 85, 112 and 139 kg N ha⁻¹ (designated as N₃₀, N₈₅, N₁₁₂ and N₁₃₉). In 2006, both the irrigation and N treatments applied were: 60, 100 and 140% ETc (I₆₀, I₁₀₀ and I₁₄₀) and 93, 243 and 393 kg N ha⁻¹ (N₉₃, N₂₄₃ and N₃₉₃). Moderate water stress did not reduce melon yield and high IWUE was obtained. Under severe deficit irrigation, the yield was reduced by 22% mainly due to decrease fruit weight. The relative yield (yield/maximum yield) was higher than 95% when the irrigation depth applied was in the range of 87-136% ETc. In 2006, the interaction between irrigation and N was significant for yield, fruit weight and IWUE. The best yield, 41.3 Mg ha⁻¹, was obtained with 100% ETc at N₉₃. The flesh firmness and the placenta and seeds weight increased when the irrigation level was reduced by 60% ETc. The highest NAE was obtained with quantities of water close to 100% ETc and increased as the N level was reduced. The highest IWUE was obtained with applications close to 90 kg N ha⁻¹. The I₂₄₃ and I₃₉₃ treatments produced inferior fruits due to higher skin ratios and lower flesh ratios. These results suggest that it is possible to apply moderate deficit irrigation, around 90% ETc, and reduce nitrogen input to 90 kg ha⁻¹ without lessening quality and yields.     

Carbon and nitrogen cycling in a tropical Brazilian soil cropped with sugarcane and irrigated with wastewater

Carbon (C) and nitrogen (N) dynamics in agro-systems can be altered as a consequence of treated sewage effluent (TSE) irrigation. The present study evaluated the effects of TSE irrigation over 16 months on N concentrations in sugarcane (leaves, stalks and juice), total soil carbon (TC), total soil nitrogen (TN), NO₃⁻-N in soil and nitrate (NO₃⁻) and dissolved organic carbon (DOC) in soil solution. The soil was classified as an Oxisol and samplings were carried out during the first productive crop cycle, from February 2005 (before planting) to September 2006 (after sugarcane harvest and 16 months of TSE irrigation). The experiment was arranged in a complete block design with five treatments and four replicates. Irrigated plots received 50% of the recommended mineral N fertilization and 100% (T100), 125% (T125), 150% (T150) and 200% (T200) of crop water demand. No mineral N and irrigation were applied to the control plots. TSE irrigation enhanced sugarcane yield but resulted in total-N inputs (804-1622 kg N ha⁻¹) greater than exported N (463-597 kg N ha⁻¹). Hence, throughout the irrigation period, high NO₃⁻ concentrations (up to 388 mg L⁻¹ at T200) and DOC (up to 142 mg L⁻¹ at T100) were measured in soil solution below the root zone, indicating the potential of groundwater contamination. TSE irrigation did not change soil TC and TN.