Formation of yield in crop cultivation is affected by influence of many factors. Simple summation of individual factors is quite rare occasion. Interaction among factors is a dynamic value. The effect of interactions varies depending on the crop development stages as well as by graduation of factors. The study aimed to evaluate the soil penetration resistance effect on winter wheat grain yield and development. It allows specifying recommendations for soil treatment difference criteria for use in site-specific soil tillage. Field trials were carried out at the Research and Study farm Vecauce of Latvia University of Agriculture during the years 2005-2007 to investigate factors influencing formation of winter wheat grain yield. Forty seven points (distributed as grid 50x50 m) were selected in the winter wheat Triticum aestivum L. field. All points were attached to their geographic coordinates. Data shows significant effect of soil resistance to grain yield - increase of soil penetration resistance by 100 kPa cmE-2 reduced yield of winter wheat by 0.37 to 0.48 t haE-1. By contrast in 2007 a significant linear regression relationship between soil penetration resistance and the yield was not detected. Differences of fresh weight of winter wheat plants in tillering stage and the beginning of stem elongation were insignificant compared to different groups of soil penetration resistance at soil layers 0.10-0.30 m in both experimental years. Higher impact of soil penetration resistance on flag leaf area difference had soil resistance at the layer of 0.20 - 0.30 m and differences were significant in both trial years.

Progeny testing of Scots pine in Latvia is carried out in only few locations, however, material from selections via seed orchards is deployed in various climatic and soil conditions, therefore concerns arise for influence of genotype environment interaction on levels of genetic gain. Problem is addressed based on 3 open pollinated progeny tests, consisting of 80 open pollinated families, located in 3 distant climatic regions in Latvia. Test age is 27 years, therefore not only growth, but also branch quality traits can be reliably analyzed. Strong genetic correlation (rb=0.80-0.94) among sites for tree height and diameter was found, but considerably weaker for branch traits like diameter of thickest branch (rb=0.52-0.67), average branch diameter, and sum of branch diameters (rb=0.41-0.49). Coefficients of additive genetic variation and coefficients of phenotypic variation among family means, determining potential of improvement via breeding, can be inflated by up to half, based on single site estimates for growth traits and double for quality traits. Backward selection based on results of several trials, in contrast to forward selection or utilization of single experiment results, could lead to improvement of branch traits close to the same as for growth traits (height and diameter). Single site narrow-sense heritability estimates for analyzed growth and quality traits are up to twice as large as across site estimates, indicating possibilities of serious bias in genetic gain estimates based on results from one test site. Testing at 4-5 sites for further breeding work is recommended.

A current investigation compared various intensive crop rotations (Norfolk, row crops, cereals, short term grass) grown on Cambisols. The study results showed significant effects of N-fertilization of the agroecosystem on mineral N concentration in drainage water and its leaching process. The highest N concentration in drainage water and leaching was determined in the conditions of cereals and row crops rotations. No major impact of the crop rotation on phosphates concentration in drainage water was determined. The average leaching of one by drainage did not exceed 100-140 g haE-1 within a 7 year study period. An experiment was arranged during 1997-2003 years in the Kėdainiai district, Lipliunai willage. A rational and well-considered fertilization ensures high crop productivity and profitable farming as well as steady, which is the main condition for reduced non-point source pollution of water.

The paper overviews the research material related to occurrence of sinkholes and change of their water quality in the conditions of increasingly natural environment and minimal anthropogenic impact. Sinkholes create favourable conditions for interaction of surface and groundwater. Identification of possible sources of sinkholes pollution is very important in solution of groundwater safety problems. Water quality investigations are carried out in 4 sinkholes, which are of different age and have differently overgrown slopes. Sinkhole water quality may worsen due to accumulation of organic materials (increasing peat content) or natural changes of environment (abrasion of slopes, overgrowth, etc.), while anthropogenic impact is minimal. Water quality in peat-filled sinkholes and young sinkholes with mineral slopes is different. Water of peat-filled sinkholes has bigger amounts of N-NO3, PTotal, SO4 and BOD7 than water in young sinkholes. The highest N-NO3 and SO4 concentration is observed in the sinkhole that is overgrown with trees and shrubs.

Severe damages of spruce stands were found during recent years in several countries of the Baltic sea region. Characteristic indications of these damages are trees with brownish drying tops distributed across the whole compartment. During the first year only forests on drained organic soils suffer. In the second and third years, according to experiences gained in Lithuania, the damages move to other stand types. In Latvia, the first signals about the damages of spruce stands arrived from the company ''Rīgas meži'' in May, 2010. ''Rīgas meži'' found damaged stands in 2 forestries. The most of the damaged stands were on organic soils. The inspection of other forests by the State forest service identified similar damages in Southern part of Latvia as well as in other regions with considerable areas of organic soils. In August, 2010 ''Rīgas meži'' did their own inspection in Olaine and Tīreļi forestries and found out that 24% of spruce stands has characteristic signs of damages, and in 10% of stands dead or significantly damaged trees were found. Due to theses damages, about 300 ha of spruce stands were harvested in sanitary clear-felling in 2010. Spreading of spruce bud scale, Physokermes piceae (Schrnk.), is found to correlate with damages of spruce stands in Latvia and Lithuania. This pest is well known in both countries, but never before it caused any serious damages to spruce stands. In Sweden another bud scale insect (Physokermes inopinatus Danzig and Kozár) is found to be the reason for spruce damages.

To promote the future of abandoned lands management and the reduction of fossil energy consumption in Latvia, the establishment of energy crops plantation facilities, including perennial grasses, was investigated. The objective – suitability of several perennial grasses for bio-energy production under condition of Latvia. The aim of the current research to evaluate the experimental field conditions for the cultivation of perennial grasses. The perennial grasses are modest in terms of soil conditions, they are environmentally friendly, as well as provide high yields of biomass with adequate quality for bio-energy production without large investments. With increasing amounts of bio-energy production the amounts of various by-products which are profitable to utilize as energy crops fertiliser will also increase. It is essential that plant nutrients return back into circulation by creating a complete cycle. In order to test in practice the possibility of creating this complete cycle of growing perennial grasses, an experimental field was chosen at the Research Institute of Agriculture in Skriveri. In the summer of 2011, before trials establishment, the conditions of soil were examined at four depths: 0 – 20 cm; 20 – 40 cm; 40 – 60 cm and 60 – 80 cm. The analyses showed that the experimental field conditions were appropriate for growing of perennial grasses. The results of the soil agrochemical analysis will be a base for future studies of usage efficiency of different fertiliser types on perennial grass productivity and nutrient recycling opportunities in energy crop plantations.

Blueberry cultivation is becoming more and more popular in Latvia, and several commercial plantations have been established recently. Highbush blueberries (Vaccinium corymbosum L.) are perennial and can grow without replanting for 50 years; therefore a choice of soil and its preparation have a great role. This article summarizes results of research carried out in commercial blueberry plantation established in 2004 on loamy Haplic Cambisol. Soil properties, especially reaction and organic matter content, initially were not suitable for blueberry cultivation, therefore deep tillage and application of soil conditioner (acid sphagnum peat) were done before planting and similar peat mulch was applied every second year. Berry yield of 4 blueberry cultivars, soil properties and the nitrogen, phosphorous and potassium content in growing plant leaves were determined. The obtained results showed that sphagnum peat is an effective material for lowering of soil pH in plant root layer (0 – 40 cm). Data about plant nutrient content in topsoil and subsoil as well as in growing plant leaves will help to develop criteria for soil fertility assessment and diagnosis of plant nutrition.

The research was carried out on ASU WRI grounds in Juodkiškes village in Endocalcari Endohypogleyic Cambisol (CMg-n-w-can). Research basis is 3 different field studies. In Variant I an organic cropping system was used with manure and without mineral fertilizers and pesticides, in II - organic-mineral cropping system with manure and mineral fertilizers, using pesticides, in Variant III - mineral cropping system with mineral fertilizers and pesticides. Minimum mineral nitrogen content in soil was in the organic cropping system, and the total minimal field crop capacity - in the mineral cropping system. However, it has the highest energy efficiency of this system (ETK - 13). Minimal N-NO3 - concentration in drainage water was in the mineral cropping system. In the organic-mineral and organic cropping systems concentration of this compound increases by 11 percent (to 21.8 mg l-1). The minimal concentration of ammonia nitrogen was under organic cropping conditions. The organic cropping system showed the highest runoff and maximum leaching of nitrogen compounds by drainage.

Organic farmers need varieties adapted to variable growing conditions, because in organic farms environmental conditions significantly vary in soil nutrient status, weed and disease pressure not only between years, but also among farms within a season. Modern varieties developed under high input agricultural systems do not always perform well under organic growing conditions. Therefore, farmers need such varieties of cereals that can adapt to variable growing conditions and maintain productivity. One of the ways to promote adaptation to environment is growing of variety mixtures. Field trials were conducted during 2014 – 2016 under organic and conventional farming systems in two locations with an aim to estimate the advantages of barley mixtures in respect of yield and its stability. The trial consisted of eight mixtures of barley varieties and breeding lines, components of mixtures in pure stand and three check varieties. The mixtures were combined by using two, three and five components. Three mixtures, each in one out of 11 environments significantly out–yielded, but one mixture had significantly lower yield than the average value of their components. Some mixtures showed a tendency to out–yield the average of components in both farming systems. All mixtures insignificantly out–yielded check varieties in 2015, but in 2016, yield was within the range between varieties with lowest and highest yield. The results of yield stability analysis showed that mixtures could be used as one of the approaches to stabilize yield – only one of eight mixtures had a lower yield than the average over all environments.

The purpose of the study was to compare forest and postagrogenic soils by parameters such as carbon content in organic matter and total nitrogen to predict the fertility state of lands that are at the stage of restoration of woody vegetation. Areas with similar soil formation conditions were selected on the postagrogenic and forested lands having mature forest stands related with such types of forest: Myrtillosum forest, Oxalidosum and Herbosa-Composita forest, and also areas under the soil complexes of postagrogenic fallow lands. A number of physico-chemical indicators for the soil were assessed according to the methods generally accepted in soil science: the particle size distribution, the bulk density and the thickness of the pedogenic horizons were determined. An analysis of the carbon stocks in organic matter (Corg) and nitrogen (Ntotal) in the genetic horizons of the soils of myrtillosum, Oxalidosum and Herbosa-Composita forest types shows an increase in the content of organic matter and total nitrogen from Myrtillosum to Herbosa-Composita forest type. A comparative analysis of the physical and agrochemical state of postagrogenic and forest soils showed that, despite the previous anthropogenic impact, the agroland horizon retains a high content of organic matter and total nitrogen. The properties of postagrogenic soils in the studied areas are not deteriorated, and the transformation towards the natural forest soils of the region is not observed, despite the long period of fallowing.