Сельское хозяйство/3. Земледелие, грунтоведение и агрохимия

Candidate of agricultural sciences Shilov M.P., first-year student of the agro-biological faculty Kapenova A.A

Republican state enterprise 'A.Baitursynov Kostanay State University',

Kazakhstan

Soil-protective fallow in the steppe zone of Northern Kazakhstan

Due to erosion bare fallow is the most vulnerable type of a field in the soil-protective agriculture. No matter what machine-based technology is used there is always a potential danger of starting erosive processes. Therefore one needs to reduce the period of bare fallowing by sowing a covering crop in order to decrease wind erosion.

Experiments were carried out on southern chernozems of Kostanay region in 2007-2011. Bare fallow was prepared according to zonal technology with the help of four small (10-12 cm) subsurface cultivations. Basic soil processing was carried out according to the outline of the experiment (Table 1). The fallow was bare in the first half of summer. Pea mixed with oat was sowed in the second half of summer and cropped herbage in the second decade of September.

Research proves intensive erosion of soil aggregates under the influence of operating elements and weather conditions. This process is especially active in the case of bare fallow, because the sum of mechanical influences on the soil is very big, and the surface is open to the impact of external factors for a long time (Table 1). In such conditions the degree of diffusion of the upper layer is significantly high. By the end of fallowing, which is carried out with the help of subsurface plows, the initially high lumpiness (64.3%) drop to the critical level of 49.7-50.9 %. While using chisel cultivators and plows these values are 51.6 and 55.5 %. In all cases the soil changes its quality from reliably to the moderately wind-firm with the erodibility of 77.2-89.4 g. It means that if the wind becomes as strong as 12.5 m/sec. or stronger theerosive processes are quite possible. This state of the surface was observed for 4 years out of 5, and once the soil was vulnerable to the wind. This allows to speak about annual actual danger of wind erosion of bare fallow.

Table 1

Lumpiness coefficients (numerator, %) and erodibility indices (g) in the layer of 0-5 cm at various technologies of fallowing at the beginning and end of the period

Fallow type	Years of experiments					On the average
	2007	2008	2009	2010	2011
Beginning of fallowing	64.8 6.8	70.3 8.2	68.5 2.5	57.3 0	60.5 28.3	64.3 9.2
25-27 cm deep subsurface cultivation at the end of fallowing (control)
bare fallow	50.2 87.9	44.7 136.4	59.4 41.2	42.5 101.4	54.6 72.8	50.3 87.9
cropped fallow	62.5 6.1	55.4 16.7	70.6 0	54.9 15.0	67.5 2.1	62.2 8.0
33-35 cm deep chisel cultivators at the end of fallowing
bare fallow	51.8 77.4	46.1 122.0	57.9 45.2	44.7 82.5	57.5 58.8	51.6 77.2
cropped fallow	64.8 4.9	57.7 12.3	67.2 0	52.4 16.7	63.1 3.1	61.0 7.4
10-12 cm deep subsurface plow processing at the end of fallowing
bare fallow	49.4 90.7	43.3 147,2	58.8 41,2	41.6 99,0	55.2 69,0	49.7 89,4
cropped fallow	65.2 3.8	56,0 12.5	69,4 0	55,8 11.3	65,1 1.9	62,3 5.9
25-27 cm deep plowing in the middle of the fallowing period
bare fallow	54.5 78.8	49.6 112.9	65.3 35.6	47.2 134.6	60.7 49.9	55.5 82.4
cropped fallow	68.1 4.2	60.3 18.0	75.6 0	56.2 29.6	71.3 1.4	66.3 10.6

No essential differences are revealed among autumn devices of the basic subsurface tillage of bare fallow. Wind-firmness indexes were within the limits of one gradation of erodibility. Some increase in lumpiness in the cases of deep subsurface and chisel cultivation is caused by dropping of pulverous particles and carrying structural jointing on the surface with the operating elements tools.

Plow processing in the middle of fallowing puts the pulverised upper layer on the furrow bottom and puts up structural aggregates having water-stability over 55% and cohesion over 65 %. However to keep the soil in the wind-firm state without any plant remnants on its surface is possible only if the lumpiness coefficient is 60 % or more. It was possible to reach this level in the rainy summers 2009 and 2011 when erodobility did not exceed 50 g. In the erosinally dangerous weather characterized by a small amount of precipitation and high dryness of the air the diffusion rate of soil aggregates is big. In 2008 the lumpiness of the upper layer reached the threshold of wind-firmness and in 2010 it was lower it with the coefficient of 47.2%.

Cropped fallow possesses a considerably bigger soil-protective efficacy than bare fallow. Instability of a soil lump is compensated by the protection of the soil-covering culture. Thus sowing pea mixed with oat in the second half of summer not only confines the process of wind-firm aggregates diffusion (2008, 2010), but also forms them to the initial level (2007), and in separate congenial years also helps exceed it (2009, 2011). Therefore by the end of fallowing the difference in lumpiness between bare fallow and cropped fallow reaches 10.6-12.6 %. Together with a considerable quantity of plant remnants it provides reliable protection of the soil surface against wind erosion. In all the years of experiments the soil state was characterised as strongly wind-firm with the average erodibility 5.9-10.6 g.

The influence of the basic processing techniques on the wind-firmness was not essential because its indexes in all the cases were within the same limits. Some variation is a consequence of different terms and depth of cultivation. So, autumn tillage had the single influence bound to degree of safety of an eddish. Thus the advantage small subsurface cultivation lies in the decrease in erodibility to 5.9 g. Penetrating plowing in the middle of fallowing surpasses other variants in size lumpiness on 4.1-5.0 per cent and concedes to them in erodibility (10.6 g).

The advantage of cropped fallow in forming a steady surface remains in spring, the most erosion dangerous the season. Prior to sowing wheat it provides reliable annual protection of soil against the influence of external factors. Indexes of lumpiness and erodibility prove it (in the cases of wheat sowing the average indices were 57.6-62.1 % and 15.1-19.2 g. The surface of the bare fallow has moderate (weak) stability to erosive processes. Its erodibility reached 73.9-76.0 %.

The change analysis of lumpiness from autumn to spring has not revealed any of the basic processing techniques. To a greater degree the changes depended on the weather factors. In general, the changes were concerned with the loss of lumpiness in the cropped fallow and its restoration in the bare fallow. The exception was registered only in 2009, when decrease in wind-firm fraction was observed in all the cases due the very early and dry spring. Perhaps, the process is characterized by the tendency to achieve some certain average lumpiness which it has acquired during a long agricultural use. As a result of it changes the interrelation of lumpiness of the bare and cropped fallow is changing. In comparison with autumn indexes the difference between them contracts to a minimum, with 10.2-12.6 to 5.9-6.7 %.

As a whole, the experimental results show that the old arable chernozem possesses weak stability to wind erosion. Therefore the technology of bare fallowing creates real annual danger of erosive processes. In the cropped fallow the weakness of a soil-protective lump is compensated by protection of the covering crop. Its soil-protective efficacy is displayed in the season of fallowing and in the first year of sowing wheat.