Using the DRAINMOD-N model to study effects of drainage system design and management on crop productivity,profitability and NO3–N losses in drainage water

The environmental impacts of agricultural drainage have become a critical issue. There is a need to design and manage drainage and related water table control systems to satisfy both crop production and water quality objectives. The model DRAINMOD-N was used to study long-term effects of drainage system design and management on crop production, profitability, and nitrogen losses in two poorly drained soils typical of eastern North Carolina (NC), USA. Simulations were conducted for a 20-yr period (1971–1990) of continuous corn production at Plymouth, NC. The design scenarios evaluated consisted of three drain depths (0.75, 1.0, and 1.25 m), ten drain spacings (10, 15, 20, 25, 30, 40, 50, 60, 80, and 100 m), and two surface conditions (0.5 and 2.5 cm depressional storage). The management treatments included conventional drainage, controlled drainage during the summer season and controlled drainage during both the summer and winter seasons. Maximum profits for both soils were predicted for a 1.25 m drain depth and poor surface drainage (2.5 cm depressional storage). The optimum spacings were 40 and 20 m for the Portsmouth and Tomotley soils, respectively. These systems however would not be optimum from the water quality perspective. If the water quality objective is of equal importance to the productivity objective, the drainage systems need to be designed and managed to reduce NO₃–N losses while still providing an acceptable profit from the crop. Simulated results showed NO₃–N losses can be substantially reduced by decreasing drain depth, improving surface drainage, and using controlled drainage. Within this context, NO₃–N losses can be reduced by providing only the minimum subsurface drainage intensity required for production, by designing drainage systems to fit soil properties, and by using controlled drainage during periods when maximum drainage is not needed for production. The simulation results have demonstrated the applicability of DRAINMOD-N for quantifying effects of drainage design and management combinations on profits from agricultural crops and on losses of NO₃–N to the environment for specific crop, soil and climatic conditions. Thus, the model can be used to guide design and management decisions for satisfying both productivity and environmental objectives and assessing the costs and benefits of alternative choices to each set of objectives.     

The effects of crop load and irrigation rate in the oil accumulation stage on oil yield and water relations of ‘Koroneiki’ olives

The interactions between irrigation rates applied during the oil accumulation stage and crop load were studied in a six-year-old very-high-density Koroneiki (Olea europaea L.) orchard. Five irrigation rates, determined as thresholds of midday stem water potential, were applied from July 1st until harvest in 2008 and 2009 and from July 1st to the end of September in 2010. Oil yield increased with increasing crop load in all the irrigation treatments. Oil yield did not respond to increasing irrigation at very low crop load and the higher the crop load the higher the response to irrigation. There was no response to irrigation at the lowest crop loads, but the higher the irrigation rate the higher the oil yield at high crop loads. The predicted commercial oil yield at common fruit counts increased from 1.99 t/ha at the lowest irrigation rate to 3.06 t/ha at the highest irrigation rate. Stomatal conductance decreased with decreasing stem water potential but leveled off at 30–60 mmol m^?2 s^?1 at stem water potential values lower than ?4.0 MPa. High crop load increased stomatal conductance and decreased stem water potential relative to low crop load at low and medium irrigation rates. The effect of crop load on water relations became evident by the end of August and was well pronounced at the beginning of October. Physiological and irrigation water management implications related to the interactions between tree water status and crop load are discussed.     

Options for alternative irrigation water supplies in the Murray–Darling Basin,Australia: a case study of the Shepparton Irrigation Region

Irrigated agriculture in the Murray–Darling Basin (MDB) currently faces serious challenges due to water scarcity, degradation of water quality, waterlogging and salinity resulting from inappropriate water and land use practices. In particular, there is now increasing risk of water quality degradation due to nutrient rich drainage water in the river system. Therefore, the future of irrigation will depend on the strategies that protect water quality and make best use of water available in the Basin. In this paper, we examine various options that irrigators have to augment water supplies on their farms using the Shepparton Irrigation Region (SIR), Victoria, as a case study. Here, we also discuss the suitability of the ‘Drainage Water Storage Scheme’ (DWSS) in providing additional water supplies to irrigators and in reducing the risk of water quality degradation due to flow of nutrient rich runoff into Basin’s river systems.     

A bio-economic modelling project for small-scale milk production systems in South-East Brazil: Part 2—refinement and use of the model to analyse some short- and long-term management strategies

The further development and use of a bio-economic model to simulate small-scale dairy enterprises in South-East Brazil are reported.The account of animal nutrition has been refined to take account of protein requirements in addition to energy balance. A new version has been developed which allows for the inheritance of production traits.The model has been used to analyse the effects of short-term management decisions on feeding strategies and longer term breeding policies for herd development. It has been used, also, to examine the possibilities of culling for reproductive performance and the effects of a range of growth rates of replacement heifers on overall herd performance.     

Identifying irrigation zones across a 7.5-ha ‘Pinot noir’ vineyard based on the variability of vine water status and multispectral images

Vine water status, yield and berry composition are variables within a vineyard. There is current interest in defining zones of similar yield and berry composition. The aim of this study was to compare two methods for identifying zones of similar yield within a 7.5-ha ‘Pinot noir’ vineyard. The two methods were based on: spatial distribution of average midday leaf water potential (Ψ_L) and plant cell density (PCD?=?near-infrared/red) which is a vegetation index. A proposal for splitting the vineyard into eight new irrigation zones was assessed. A ‘blind’ zonation based on regular polygons of equal sizes was also established as a standard for comparison. Coefficients of variation (C _v) in yield for both methods were compared with that of the blind zonation. In 2006 and 2007, a k-means cluster analysis indicated that variability in Ψ_L was mainly effected by soil properties. In both years, the vineyard was fully irrigated (100?% ET_c). The two methods did not improve yield C _v for full irrigation in 2006 and 2007 compared to blind zonation. In 2009, regulated deficit irrigation (RDI) was applied resulting in higher variability in Ψ_L and yield. The Ψ_L method of zonation significantly reduced coefficient of variation under RDI but PCD method did not despite the reduction in C _v by 16.7?%. We recommend irrigation zonation based on Ψ_L when RDI is applied.     

Salt distribution in the Senegal middle valley: Analysis of a saline structure on planned irrigation schemes from N’Galenka creek

In the middle Senegal valley, the saline soil distribution is not related to the present faint topography. The absence of a relationship is one of the major constraints in establishing new irrigation schemes. The salt distribution was studied to understand its variability, and to describe its structure and spatial arrangement. Saline areas were delineated by measuring the electromagnetic soil conductivity (ECm), a rapid technique with a portable instrument (EM38). The results indicate that the saline soils are distributed as strips. A detailed examination revealed that the major strip is actually composed of two parallel minor strips, and a comparison with aerial photographs showed that one lies in a former creek bed, and the other fringes it on the southern bank. The strip is intersected by an actual creek bed, indicating that the salt distribution is ancient, related to previous geo-morphology, and does not result from a recent remobilisation of the marine salt deposits incorporated in the soil. The identification of this relationship between the present saline soil distribution and previous geo-morphology allowed us to survey the whole N’Galenka region (about 6000 ha) using ECm measurements on selected transects.     

Effects of different irrigation regimes on a super-high-density olive grove cv. “Arbequina”: vegetative growth,productivity and polyphenol content of the oil

The effects of multiple irrigation regimes on the relationships among tree water status, vegetative growth and productivity within a super-high-density (SHD) “Arbequina” olive grove (1950 tree/ha) were studied for three seasons (2008–2010). Five different irrigation levels calculated as percentage of crop irrigation requirement using FAO procedures (Allen et al. in Crop evapotranspiration. Guidelines for computing crop water requirements. Irrigation and drainage paper 56. FAO, Rome, 1998) were imposed during the growing season. Periodically during the growing season, daytime stem water potential (Ψ _STEM), inflorescences per branch, fruits per inflorescence and shoot absolute growth rate were measured. Crop yield, fruit average fresh weight and oil polyphenol content were measured after harvest. The midday Ψ _STEM ranged from ?7 to ?1.5 MPa and correlated well enough with yield efficiency, crop density and fruit fresh weight to demonstrate its utility as a precise method for determining water status in SHD olive orchards. The relationships between midday Ψ _STEM and the horticultural parameters suggest maintaining Ψ _STEM values between ?3.5 and ?2.5 MPa is optimal for moderate annual yields of good quality oil. Values below ?3.5 MPa reduced current season productivity, while values over ?2.5 MPa were less effective in increasing productivity, reduced oil quality and produced excessive crop set that strongly affected vegetative growth and fruit production the following season. On the basis of the result given here, irrigation scheduling in the new SHD orchards should be planned on a 2-year basis and corrected annually based on crop load. Collectively, these results suggest that deficit irrigation management is a viable strategy for SHD olive orchards.     

Effects of the measures envisaged in “Agenda 2000” on arable crop producers and beef and veal producers: an application of Positive Mathematical Programming to representative farms of a Spanish region

The authors analyse the possible effects of the measures envisaged in “Agenda 2000”, approved by the Berlin European Council of March 1999, on representative farms specialised in arable crop production and beef and veal production. Three economic sizes are considered for each of these types of farming (4–16 European Size Units [ESU], 16–40 ESU and >40 ESU). The analysis is made by means of Positive Mathematical Programming, utilising quadratic cost functions. The results show that the increase in compensatory payments and premiums would not offset a possible decrease in market prices, and therefore, for most of the agricultural holdings studied, the economic results worsen. It is worth noting that the total subsidies share in agricultural incomes is notably increased.