Field experiments were conducted for 2 years to investigate the effects of various levels of nitrogen (N) and methods of cotton planting on yield, agronomic efficiency of N (AEN) and water use efficiency (WUE) in cotton irrigated through surface drip irrigation at Bathinda situated in semi-arid region of northwest India. Three levels of N (100, 75 and 50% of recommended N, 75 kg ha?1) were tested under drip irrigation in comparison to 75 kg of N ha?1 in check-basin. The three methods of planting tried were; normal sowing of cotton with row to row spacing of 67.5 cm (NS), normal paired row sowing with row to row spacing of 35 and 100 cm alternately (NP) and dense paired row sowing with row to row spacing of 35 and 55 cm alternately resulting in total number rows and plants to be 1.5 times (DP) than NS and NP. In NS there was one lateral along each row, but in paired sowings there was one lateral between each pair of rows. Consequently the number of laterals and quantity of water applied was 50 and 75% in NP and DP, respectively, as compared with NS in which irrigation water applied was equivalent to check-basin.
Drip irrigation under NS resulted in an increase of 258 and 453 kg ha?1 seed cotton yield than check-basin during first and second year, respectively, when same quantity of water and N was applied. Drip irrigation under dense paired sowing (DP) in which the quantity of irrigation water applied was 75% as compared with NS, further increased the yield by 84 and 101 kg ha?1 than NS during first and second year, respectively. Drip irrigation under NP, in which the quantity of water applied and number of laterals used were 50% as compared with drip under NS, resulted in a reduction in seed cotton yield of 257 and 112 kg ha?1 than NS during first and second year, respectively. However, the yield obtained in NP under drip irrigation was equivalent to yield obtained in NS under check-basin during first year but 341 kg ha?1 higher yield was obtained during second year. The decrease in N applied, irrespective of methods of planting, caused a significant decline in seed cotton yield during both the years. Water use efficiency (WUE) under drip irrigation increased from 1.648 to 1.847 and from 0.983 to 1.615 kg ha?1 mm?1 during first and second year, respectively, when the same quantity of N and water was applied. The WUE further increased to 2.125 and 1.788 kg ha?1 mm?1 under DP during first and second year, respectively. The agronomic efficiency of nitrogen was higher in drip than check-basin during both the years when equal N was applied. The WUE decreased with decrease in the rate of N applied under fertigation but reverse was true for AEN. It is evident that DP under drip irrigation resulted in higher seed cotton yield, WUE and AEN than NS and also saved 25% irrigation water as well as cost of laterals.
In the present day context, lot of emphasis is being given on improvements in irrigation practices to increase the crop production and to sustain the productivity levels. The wasteful and harmful system of flood irrigation (check-basin) practiced widely in South Asia must be replaced with furrow, drip or sub-irrigation systems. Many researchers have reported higher yields and water use efficiency (WUE) of drip irrigation system over the conventional irrigation methods throughout the world. Using same quantity of water, partial root drying simulating drip irrigation, resulted higher shoot biomass compared with uniform watering simulating flood irrigation. In drip irrigation the volume of wetted soil at a particular water application is controlled by the volume of water added, the discharge rate of dripper and the soil water content. Drip method of irrigation is most suited to semi-arid and arid areas where water is scarce and where low water consuming and high value crops can be grown. Cotton (Gossipium hirsutum L.) is one of the most important fiber producing plant throughout the world. Drip method of irrigation is being practiced for cultivation of cotton in many countries such as USA, Israel , Spain and Turkey. In India, drip irrigation in cotton is being practiced by some farmers in the states of Gujarat, Madhya Pradesh and Maharashtra in heavy textured soils. But in Indo-Gangetic plains where the soils of cotton growing region are light in texture and underground water is brackish, drip irrigation to cotton is at experimental stage. At present farmers’ grow cotton in rotation with wheat by applying four to five irrigations to each crop through boarder method (check-basin). The depth of irrigation water is nearly 75 mm per irrigation, which costs Indian rupees (Rs.) 250 ha?1 (US$ 1 = 40 Rs.) for its pumping and application. With these irrigations and soil test based recommended fertilizers, the average observed yields of seed cotton and wheat in Punjab state are 1242 and 4221 kg ha?1, respectively. In this region the only source of water for irrigation is river water supplied through canals. There is great need for judicious use of canal water because excess usage causes deep percolation resulting in high water table and secondary salinization. The water logging and secondary salinization has already resulted in degradation of land resources in adjoining districts and state of Haryana. The judicious use with minimal deep percolation of available canal water is the need of the hour for sustaining the land resources.
Drip irrigation improves the water use efficiency, nutrient uptake and quality of the produce. The higher fruit yield, total soluble solids and sugars in watermelon under drip irrigation were accompanied by higher uptake of N, P, K, Ca and Mg than under furrow irrigation. The fruit yield of okra was significantly increased when fertilizer was applied through drip than band placement. The fertigation of chilli with 100% recommended N saved 40% water and produced 52% higher yield over check-basin and only 50% N applied through fertigation produced equivalent amount of fruit to check-basin. Yield of onion and total available NO3-N was not significantly affected in daily, alternate day and weekly fertigation frequency confirmed, by the use of 15N, that fertilizer N utilization efficiency was lower with soil application than fertigation and fertigation also improved WUE. On the other hand, under deficient water conditions the effectiveness of mineral N-fertilizer is reduced due to reduced mineralization of soil organic N as well as impaired N-transport to roots as root growth, physiological activity of roots and shoot growth are constrained, shortage of water indirectly leads to N-deficiency in plants. The major drawback of the drip irrigation system is its high initial cost, however, the cost can be recovered in a short span if proper nutrient and water management along with proper design principals are followed. Among the various components of drip irrigation system, the cost of laterals is the major factor, which influence the total system cost. Any effort made to reduce the length of laterals required per unit area of the field will result in reduction of the system cost. studied the effect of planting configuration on water use and economics of drip irrigation system and found that paired row planting reduced the cost and water use by 50%. Understanding the effects of different quantities of N and water applied through drip and check-basin methods of irrigation under same set of soil and climatic conditions on yield and WUE in cotton is critical to formulate proper management practices for sustainable production. In a previous study the authors observed that under drip irrigation system seed cotton yield increased by 32% and WUE by 26% under normal sowing. But under paired sowing, which saved 50% irrigation water as well as the cost of laterals, a decline of 9% in yield but improvement in WUE by 24% was observed as compared with drip under normal sowing. However, the yield under paired sowing was 20% higher than normal sowing under check-basin. In check-basin method the yield also declined by 16% under paired sowing than normal sowing although the quantity of water applied was same. The results suggest that paired sowing under wider spacing of 100 cm and closer spacing of 35 cm in alternate rows was inferior to equally spaced rows of 67.5 cm. Thus, the present investigation was undertaken to evaluate if increased number of rows under paired sowing may improve the yield and water use efficiency. The objective of the present investigation was to determine the independent and interactive effects of various levels of N and different quantities of water applied to paired sown cotton at different densities through drip irrigation on seed cotton yield, and agronomic efficiency of N (AEN) and water use efficiency.
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