The major emphasis in the conference was on promoting various resource conservation technologies for tillage and crop establishment of rice, wheat and other crops in the rice-wheat systems. Due to declining water resources and high water requirements of traditional puddled rice transplanting in wheat–rice cropping system, various technologies were discussed. Direct rice seeding (DRS) is also one of the options. Area under DRS has already increased to 26 per cent of the total rice area in South –East Asia.
In Pakistan, the traditional puddled rice transplanting in rice-wheat cropping system is followed for the last over 2000 years. Seedlings 4-6 week old are transplanted in puddled fields. Puddling is achieved by ploughing under10-12 inches of standing water. It is a soil management operation that reduces soil permeability, controls weeds, facilitates transplanting of rice seedlings raised in nurseries and reduces deep percolation losses of water to maintain anaerobic conditions that increase availability of iron, zinc and phosphorous required for healthy growth of rice. Nearly 30 per cent of total water requirement of rice is consumed mainly in puddling and transplanting operations, besides additional water is required for raising rice seedlings in nurseries.
However, continued puddling over the decades has led to deterioration in physical properties of soil through structural break down of soil aggregates and capillary pores and clay dispersion. Puddling forms a compacted layer (plough plate) that restricts percolation of water causing temporary water-logging which restricts root penetration and growth of succeeding crops after rice.
Industrialisation in the rice zones has further caused shortage of labour for timely transplantation of rice thus resulting in reduction of yield. The declining water resource base has further compounded the situation. Therefore, besides improving our water resource base, there is need to find an alternative technology that is more water efficient, less labour intensive. One such technology is direct seeding of rice (DSR) instead of the traditional puddle transplanted rice. As it avoids puddling and does not need continued submergence and thus reduces overall water requirement for rice cultivation.
But traditional agronomic practices used in DSR cultivation cause several problems to farmers such as poor germination, high early seedling mortality during a rainfall event, requiring gap filling in uneven fields, weed infestation and non-availability of effective post and pre-emergence herbicides. However, improved practices to overcome these problems have been developed in the Indo –Gangetic Plains. The salient features of DSR technology are as follows:
Planting Techniques: The best planting time of DSR will be 10 to 12 days earlier than the traditional transplantation period which will enable earlier planting of the following wheat crop resulting in its increased yield as against its traditional late sowing in wheat-rice system, especially after basmati rice which due to its longer period further delays sowing of succeeding wheat crop and a delay of one day after third week of November results in reduction of its yield by 35 kg per ha per day. Again, due to aerobic soil conditions under DSR, as required by the following wheat crop, there is no need of a number of ploughings required for changing the anaerobic to aerobic soil conditions of rice grown under traditional puddled transplanting system. Thus the zero tillage technology for sowing of wheat after DSR may be more effective. Zero tillage technology directly sows wheat seeds and applies fertiliser in one operation in the residual moisture of harvested rice stubbles. Thus it not only further reduces the delayed sowing of wheat but also saves rauni irrigation (irrigation given for seed bed preparation), cost of preparatory tillage and increasing wheat yield due to its earlier planting. According to observations at field conducted by the Directorate of On Farm Water Management (OFWM), Punjab, which introduced zero tillage in the country, it saves irrigation water by 20 per cent and increases wheat yield by 15-20 per cent.
Again, unlevelled fields cause wastage of land and low irrigation efficiencies, resulting in lower wheat yield. Nearly 20-25 per cent of water is lost during irrigation on unlevelled fields and farm designing. Thus use of laser land levelling technology on unlevelled fields will minimise cost of land preparation, save irrigation water, obtain uniform seed germination, increase fertiliser use efficiency and increase crop yield.
Seed rate and seeding depth: The seed rate for direct seeding of medium to fine grain rice varieties should be 20-25 kg per ha. Higher seed rate can reduce yield by causing nitrogen deficiency, reduced tilling, increase in the number of ineffective tillers, increased attack of brown plant hoppers and crop lodging. Seed depth should be 2-3cm for good crop stand. Placing seed below 3cm adversely affects dynamics of seed emergence because of rapid drying of soil surface in peak summers. If seed is soaked for 8 to 10 hours it advances germination. Soaked seed (priming) is dried in shade to decrease its moisture content which facilitates its free flow during seed drilling. Soaking of seed with Bavistin/Theram eliminates or reduces seed borne and soil-born diseases.
Fertiliser dose: General recommendation is to apply full dose of P and K (60 kg p2 05 and 40 kg k 2 0 per ha). Of nitrogen 80 per cent of the recommended dose should be applied at sowing and the remaining N as required using leaf colour chart (LCC). For hybrids and high yielding inbred rice LCC value of 4, while a critical LCC value of three is used for fine Basmati rice varieties. Value of LCC should be recorded after 20-25 of direct seeded rice up to its heading. It is recommended to apply a little more of N and P to DSR
Weed control: Weeds are a major concern for high productivity of DSR crop. Weed control efficiency depends on timely operations particularly during early growth stages of rice.
For chemical weed control, it is necessary to select right herbicides depending upon the weed species, and herbicides should be applied with proper spray techniques. The pre planting herbicides used to control the existing perennial weeds are Glyphosate and Parquat, while herbicides to control pre-emergence weeds are Pendimethalin ,Pretilachlor with saener. Similarly for the control of post-emergence weeds the recommended herbicides are Almix, 2, 4-D ester/sodium salt, repeated application of second dose of pendimethalin and Azimsulfuron.
Irrigation management: DSR crop does not require continuous submergence and can be safely irrigated when hairline cracks appear on the soil. However, water stress be avoided at tilling, panicle initiation, and grain filling stages which are very crucial for obtaining higher yields.
Economics of DSR: A field study by Rice-Wheat Consortium, in India indicated that comparative economics of DSR and puddled transplanted rice showed that in 67 per cent cases the farmers obtained either higher or equal yields from DSR as compared to traditional puddled transplanted rice. The 33 per cent of farmers having lower yields were due to inexperience of the farmers such as seeding in inappropriate soil moisture, deeper seeding than there cm, delayed and improper use of herbicides.
The study also showed that comparative to puddle transplanted rice, the saving in DSR was $70-102 per ha. The zero tillage induced savings in DSR were mainly through reduced cost in land preparation (77 per cent), irrigation water (15 per cent) and labour (eightper cent). Thus the overall benefits of DSR are that it saves labour, fuel, time, water besides being cost effective and gives higher net returns as compared to conventional puddled transplanted rice.
The DSR has now become part of conservation agriculture all over the world. The Director-General of Farm Water Management, Punjab, Mr. Mushtaq Gill, in collaboration with various national and international organisations had initiated in 2001 a project of sustaining crop and water management in rice-wheat system. The project includes various conservation agricultural technologies like laser land levelling, zero tillage, bed planting, direct seeding of rice, Chinese parachute rice transplanting and Sri lankan rice transplanting technologies. All these technologies significantly decrease cost of production, save water, increase yields and income both in direct seeded and transplanting rice systems.
Other areas where Pakistan can benefit, is use of Chinese wheel type combine grain planter which does sowing of seed, application of fertiliser and soil pressing in one operation and can be used on large farms.
Likewise, two wheel hand driven 12 horse power diesel Chinese tractor commanding 12 ha can be used for small, subsistent and below subsistent farms comprising nearly 50 per cent of total cultivated area of the country. It not only reduces cost of cultivation by land preparation and sowing in one operation, but also increases crop yields up to 20 per cent. As a result its use is fast spreading among small farmers of South-East Asian countries.
Again, Chinese technologies of growing high yielding dwarf varieties of rice, double cropping of short duration rice varieties in areas with longer rice growing season and high-yielding hybrid rice varieties has increased their national average yield of rice from 1500 kg per ha to nearly 4000 kg per ha now. Pakistan should also study the potential of these Chinese varieties to increase its national rice production.